Changes of influenza vaccination rate and associated influencing factors after the COVID-19 pandemic in Shanghai, China

ABSTRACT

The vaccination rate for seasonal influenza remains low in most regions of China. It is essential to understand the factors that associated with the low influenza vaccination rate in various populations after the COVID-19 pandemic. A cross-sectional survey was conducted with residents in Pudong New Area, Shanghai, China. Respondents’ vaccination condition during the 2021–2022 flu season and the reasons for receiving or not receiving influenza vaccine were investigated. Binary logistic regression was conducted to explore potential factors influencing vaccination uptake. 2,476 of 14,001 respondents received an influenza vaccine, with a total coverage of 17.68% (95% CI: 17.05%, 18.32%). Children had the highest vaccination coverage (35.68%; 95% CI: 34.02, 37.33), followed by adults (12.75%; 95% CI: 11.91%, 13.58%) and elderly individuals (11.70%, 95% CI: 10.78%, 12.62%). For children, lower household income was an significant promoting factor. For adults, factors significantly associated with vaccination were household income, sex, and education level. For elderly, factors significantly associated with vaccination were household income, education level, living state, and having underlying diseases. (P < .05)The main reason for vaccine hesitancy among children was worried about side effects (21.49%), for adults and elderly was self-rated good health (adults: 37.14%, elderly people: 30.66%). The overall influenza vaccination coverage rate in Shanghai, especially among elderly individuals, is lower than many developed countries. Appropriate strategies and programs targeting different populations need to be implemented to enhance influenza vaccine coverage.

Plain Language Summary

The vaccination rate for seasonal influenza remains low in most regions of China. However, the COVID-19 pandemic has resulted in an increase in public awareness regarding the prevention and control of infectious diseases and changes in people's health behaviors thus may leading to changes in influenza vaccination rates and vaccination willingness. We conducted a survey on the medical service utilization behavior of community residents in Shanghai, the biggest city in eastern China. The vaccination status of respondents during the 2021–2022 flu season and the reasons for receiving or not receiving the vaccine were investigated among 14,001 local residents. The influenza vaccination rate in 2021–2022 season (17.68%) was higher than that in 2018–2019 season (11.8%) in the same area. And this trend was found in population of different age groups. However, the overall influenza vaccination coverage rate in Shanghai is still low, especially among elderly, it remains inadequate to establish an immune barrier and lags behind other developed regions. For children, lower household income was an independent promoting factor. For adults, factors significantly associated with vaccination were  household income, sex, and education level. For elderly, factors significantly associated with vaccination were household income, education level, living state, and having underlying diseases. (P < .05) The main reason for vaccine hesitancy among children was worried about side effects (21.49%), for adults and elderly was self-rated good health (adults: 37.14%,elderly people: 30.66%).Efforts should be made to increase awareness of influenza vaccines according to the characteristics of different population.

KEYWORDS:

• Influenza vaccination
• COVID-19
• coverage
• children
• elder people

Introduction

Influenza poses a global challenge to public health and contributes to a high disease burden worldwide.¹ The World Health Organization (WHO) reports that annual influenza epidemics cause three to five million severe cases of influenza, leading to 650,000 deaths due to respiratory complications.² Influenza easily spreads in crowded places such as schools and nursing homes, and it is seriously harmful to pregnant women, infants, elderly individuals and people with chronic diseases. In China, influenza also has a high disease burden, especially in children and elderly individuals. The risk of influenza among children is approximately 1.5–3 times that among adults. It is estimated that during the 2010–2011 and 2014–2015 epidemic seasons, there were an average of 88,000 excess deaths from influenza-related respiratory diseases per year in China, of which 80% were elderly individuals aged above 60 years.^3,4

Influenza vaccination is the most effective intervention to reduce the risk of influenza-related illness, hospitalization, and death.¹ Due to the evolving nature of the influenza virus, the Chinese Center for Disease Control and Prevention recommends that all residents aged 6 months or older who have no contraindications receive an annual influenza vaccine.⁴ The latest influenza technical guide 2023–2024 in China points out that the influenza vaccine can effectively reduce the incidence of influenza vaccination in the elderly population, and the priority populations for vaccination are medical staff, people in nursing institutions, elderly individuals (>60 years), children (6–59 months), pregnant women and people with chronic disease.⁵

Despite the severity of influenza and the availability of safe vaccines, the influenza vaccination rate in China is very low. The survey shows that the overall vaccination rates of China in the 2020–2021 and 2021–2022 epidemic seasons were 3.2% and 2.5%, respectively.⁶ Moreover, vaccination rates for high-risk groups such as children and elderly individuals are similarly low.⁶ In a previous study conducted in the Pudong New Area of Shanghai, the vaccination rates among children (under 15 years) and elderly individuals (above 60 years) were 26.6% and 8.2%, respectively.⁷

Shanghai is a major city in eastern China and is one of the most developed cities in the world, which has experienced the first wave of COVID-19 caused by the Omicron BA.2 variant virus from March to May 2022.⁸ The COVID-19 pandemic has resulted in an increase in public awareness in prevention and control of infectious diseases and changes in people’s health behaviors,⁹ which may lead to changes in influenza vaccination rates and vaccination willingness,Therefore, the purpose of this study is to understand the vaccination rate and potential influencing factors of residents in Pudong of Shanghai in the late stage of COVID-19 through the cross-sectional investigation, which is worth studying.

We conducted a survey on the medical service utilization behavior of community residents in the Pudong New Area of Shanghai to obtain the influenza vaccination rate and determine which demographic characteristics (including sex, age, living conditions, education level, average monthly family income, self-evaluation of health status and underlying diseases) were risk factors for vaccination hesitancy and the reasons for vaccine hesitancy across different age groups. This study aimed to understand the changes in the vaccination rate and health behavior of Shanghai citizens after experiencing the first wave of the COVID-19 pandemic. The findings of the study intend to provide a scientific basis for the formulation of public health policies in the jurisdiction.

Materials and methods

Study design

We conducted a cross-sectional study in 48 community health centers in Pudong New Area in November and December 2022. To guarantee the representative of the research findings, we using a stratified random sampling method, each community health center investigated 200–400 residents and the exact number of interviewees was separately calculated based on the age proportion of the population served by the community health service center.

The inclusion criteria were (1) community residents who lived in the Pudong New Area of Shanghai for at least 6 months. (2) age among following groups: children (<15 years old), adults (≥ 15 years old and <60 years old) and elderly individuals (≥ 60 years old) by a stratified method(3)community residents had a fixed home address and contact telephone number; The exclusion criteria were (1)community residents who lived in the Pudong New Area of Shanghai for no more than 6 months; (2) children had no guardian to answer questions (3) people who have a conscious disorder or can’t answer questions accurately. We used a stratified method to collect information.

The following sample size calculation formula for a cross-sectional study was used to estimate the required sample size:

$\mathrm{N}=\frac{\mathit{\pi }(1-\mathit{\pi })\times Z_{\alpha }^2}{d^2}$

In order to meet the expected sample size of the investigation, A total of 14209 investigators we needed. Including 2855 children(<15 years old, π = 11.8%,⁷ d = 0.1π, α = 0.05), adults 6476 (≥15 years old and <60 years old, π = 5.6%,¹⁰ d = 0.1π, α = 0.05) and 4878 elderly people (≥ 60 years old, π = 7.3%,⁷ d = 0.1π, α = 0.05). (π was calculated based on the local influenza vaccination rate 2020–2021 influenza season¹⁰ and 2018–2019 season.⁷

Data sources

The survey was conducted face to face by medical workers of the community health centers. Data were collected using King Soft Document and Questionnaire Star. For children, their parents/guardians provided answers; adults provided answers for themselves; and elderly individuals either answered for themselves or were assisted by their caregivers. Self-reported influenza vaccination status was checked by medical workers according to data on the vaccination doses available on the government information system.To validate our results, all interviews were conducted in Mandarin.

The questionnaire included three parts: (1) demographic information, such as sex, age, occupation type, education level, monthly family income and underlying diseases (children: asthma, recurrent respiratory infections, eczema, allergic diseases; adults: hypertension, diabetes, heart disease, asthma, chronic bronchitis; elderly individuals: hypertension, diabetes, heart disease, chronic bronchitis);and self reported health status (2) self-reported influenza vaccination; and (3) willingness to vaccinate and related reasons or unwillingness to vaccinate and influencing factors.

A total of 3–5 data collection personnel were employed and trained at each monitoring post to select appropriate answers and to ensure that the questionnaires were completed accurately and submitted in a timely manner. Furthermore, one or two quality controllers were employed in each community health service center to conduct preliminary quality control and to clean the data of the questionnaires to ensure the smooth completion of the survey. Training was conducted prior to the investigation.

This study was carried out by Shanghai Pudong New Area Center for Disease Control and Prevention and was approved by the Ethics Committee of Shanghai Pudong New Area Center for Disease Control and Prevention. Before the survey, all participants signed an informed consent after they agreed to attend the study. The data of the study subjects were all de-identified to protect patient privacy.

Statistical analysis

Descriptive analyses were performed to examine the participants’ demographic characteristics,χ² tests were used to test the differences in vaccination coverage rate (VCR)between male and female, different self-evaluation of health situation, monthly household income and underlying disease in the whole population. Binary logistic regression models were conducted to identify the predictors of influenza vaccination uptake in three age groups respectively. Odds ratio (OR) and the corresponding 95% confidence intervals (CIs) were calculated to assess the results of the regression model. All analyses were conducted in R studio version 4.0 or SPSS v21.0. P values < .05 were considered to indicate statistical significance.

Results

Basic characteristics of respondents

A total of 14,798 participants were invited to participate in our survey, and 14,001 valid responses were obtained (Figure 1), including 3,229 from children, 6,088 from adults and 4,684 from elderly individuals. The response rate was 94.61%.

Figure 1. Flowchart of participant inclusion.

The ages of the respondents ranged from 0–96 years old, with a median age of 42 years old [(IQR): 21–65]. Females accounted for 51.90% of the sample. A total of 95.33% of respondents reported living with family or friends. More than two-thirds (68.64%) of the adults had a bachelor’s degree or above; however, only 29.16% of the elderly respondents had a high school education level or above. More than 3/4 (76.42%) of the participants self-rated their health status as very healthy/healthy. Overall, 22.48% of the children, 12.94% of the adults and 61.23% of the elderly individuals had underlying diseases(Table 1).

Table 1. Characteristics of survey respondents in Pudong New Area, Shanghai, China, 2022.

	Overall	Children	Adults	Elderly individuals
Demographic characteristics	n = 14,001, n (%)	n = 3229 (23.06%)	n = 6088 (43.48%)	n = 4684 (33.45%)
Gender
Male	6734 (48.10)	1674 (51.84)	2827 (46.44)	2233 (47.67)
Female	7267 (51.90)	1555 (48.16)	3261 (53.56)	2451 (52.33)
Age, median (IQRa, years)	41.64 (21.12–65.45)	5.53 (3.65–8.67)	38.57 (32.38–46.25)	69.39 (65.39–74.30)
Living conditions
Living alone	654 (4.67)	—	228 (3.75)	426 (9.09)
Living with family	13347 (95.33）	—	5860 (96.25)	4258 (90.90)
Education level
Primary school	1432 (10.23)	—	97 (1.59)	1335 (28.50)
Secondary school	2833 (20.23)	—	850(13.96)	1983(42.34)
High school	2016 (14.40)	—	962 (15.80)	1054 (22.50)
Bachelor’s degree or above	4491(32.08)	—	4179 (68.64)	312 (6.66)
2021 monthly household income
(Chinese yuan)^d
<5000 RMB	3299 (23.56)	245 (7.59)	955 (15.69)	2099(44.81)
5000–10,000 RMB	5025 (35.89)	974 (30.16)	2147(35.27)	1904(40.65)
1–20,000 RMB	3312 (23.66)	1083 (33.54)	1761(28.93)	468(9.99)
>20,000 RMB	2365 (16.89)	927 (28.71)	1225(20.12)	213(4.55)
Self-evaluation of health status
Very healthy	4210 (30.07)	1455 (45.06)	2209 (36.28)	546 (11.66)
Healthy	6489 (46.35)	1513 (46.86)	2681 (44.04)	2295 (49.00)
Normal	3021 (21.58)	255 (7.90)	1116 (18.33)	1650(35.23)
Unhealthy	246 (1.76)	2 (0.06)	72 (1.18)	172 (3.67)
Very unhealthy	35 (0.25)	4 (0.12)	10 (0.16)	21 (0.45)
Underling disease
Yes	4382（31.30）	726 (22.48)	788 (12.94)	2868 (61.23)
No	9619 (68.70)	2503 (77.52)	5300 (87.06)	1816 (38.77)

Influenza vaccination coverage rate

A total of 2,476 respondents received the influenza vaccine, including 1,152 children, 776 adults and 548 elderly individuals. The overall influenza vaccination rate was 17.68% (95% CI: 17.05%, 18.32%), with 35.68% (95% CI: 34.02%, 37.33%), 12.75% (95% CI: 11.91%, 13.58%), and 11.70% (95% CI: 10.78%, 12.62%) for children, adults, and elderly individuals, respectively (P < .01). The influenza vaccination rates for males and females were 17.36% and 17.99%, respectively, which were not significantly different (P > .05). However, the influenza vaccination rate between individuals with different health statuses and different family household incomes significantly differed (P < 0.01) (Table 2).

Table 2. Coverage rates of influenza vaccination in Pudong New Area, Shanghai, in the 2021–22 influenza season.

Population characteristic	No. of individuals vaccinated	Total population	Vaccination rate (%)	95% CI (%)	χ2	p
Total	2476	14001	17.68	(17.05, 18.32)
Sex
Male	1169	6734	17.36	(16.45, 18.26)	0.008	.332
Female	1307	7267	17.99	(17.10, 18.87)
Health status
Very healthy	856	4210	20.33	(19.12, 21.55)	48.332	<.01
Healthy	1102	6489	16.98	(16.07, 17.90)
Normal	499	3021	16.52	(15.19, 17.84)
Unhealthy	19	281	6.76	(3.81,9.72)
Monthly household income
<5000 CNY	441	3299	13.37	(12.21, 14.53)	105.29	<.01
5000—10,000 CNY	827	5025	16.46	(15.43, 17.48)
10,000 Yuan—20,000 CNY	666	3312	20.11	(18.74,21.47)
>20,000 CNY	542	2365	22.92	(21.22, 24.61)
Underlying Disease
0	1782	9868	18.06	(17.30, 18.82)	5.642	.06
1	486	2996	16.22	(14.90, 17.54)
≥2	208	1137	18.29	(16.04, 20.54)

Influencing factors of influenza vaccination

For children, after controlling for all the other influencing factors, lower monthly household income (< 5000 CNY) was an independent promoting factor. The children living in families with a monthly income of less than 5,000 yuan had a higher vaccine coverage rate (VCR) (51.02%) than those with a monthly income of more than 20,000 yuan (35.38%), with an odds ratio (OR) of 1.926 (95% CI: 1.448, 2.565, P < .01).

For adults, factors significantly associated with vaccination were sex, monthly household income and education level. Women had a higher vaccination coverage rate (14.08%) than men (11.21%), with an odds ratio of 1.283 (95% CI: 1.098, 1.501, P < .05). Besides, adults with a bachelor’s degree had a higher VCR (13.81%) than those with an education level below junior high school (9.40%; OR: 1.475 95% CI: 1.148, 1.913, P < .05). Adults with a monthly household income of more than 20,000 yuan had a higher VCR than those with a monthly income of less than 5,000 yuan (15.10% vs.10.37%; OR: 1.338 95% CI: 1.015, 1.773, P < .05).

For elderly individuals, factors significantly associated with vaccination were monthly household income, education level, living statue, health condition, and having underlying diseases. Those who lived with family members had a higher vaccination coverage rate (12.19%) than those living alone (6.81%), with an odds ratio (OR) of 1.854 (95% CI: 1.272, 2.806, P < .05). Moreover, those with a monthly household income of 10,000 to 20,000 yuan had a higher VCR than those with a monthly income of less than 5,000 yuan (18.80% vs. 10.34%; OR: 1.805,95% CI: 1.342, 2.412, P < .01). Elderly individuals with a bachelor’s degree had a higher VCR than those with an education level below junior high school (19.23% vs.11.36%; OR: 1.531 95% CI: 1.096, 2.112 P < .05).The elderly with two or more underlying diseases had a higher VCR than those without underlying diseases (13.84% vs.10.30%; OR: 1.369 (95% CI: 1.051, 1.778, P < .05). Those with a very good, good or normal self-rated health status had a higher VCR than elderly individuals with a bad or very bad self-rated health status, with ORs of 2.295 (95% CI: 1.217, 4.729 P < .05); 1.911 (95% CI: 1.063, 3.808, P < .05), and 2.824 (95% CI: 1.579, 5.602, P < .05), respectively (Tables 3–5).

Table 3. Coverage rates of seasonal influenza vaccination among children in Pudong New Area, Shanghai, in the 2021–22 influenza season.

Population characteristic	No. of individuals vaccinated	Total population	Vaccination rate (%)	95% CI (%)	OR	95% CI	p	β
Total	1152	3229	35.68	(34.02, 37.33)
Sex
Male	594	1674	35.48	(33.19, 37.78)	Ref
Female	558	1555	35.88	(33.50, 38.27)	1.023	(0.885，1.182)	.762	0.022
Health status
Very healthy	522	1455	35.88	(33.41, 38.34)	1.234	(0.236，9.030)	.810	0.210
Healthy	529	1513	34.96	(32.56, 37.37)	1.187	(0.227，78.680)	.845	0.171
Normal	99	255	38.82	(32.80, 44.85)	1.344	(0.254，9.935)	.738	0.295
Unhealthy	2	6	33.33		Ref
Monthly household income
<5000 CNY	125	245	51.02	(44.72, 57.32)	1.926	(1.448,2.565)	P < .01	0.656
5000—10,000 CNY	342	974	35.11	(32.11, 35.82)	0.993	(0.823,1.200)	.947	−0.006
10,000 Yuan—20,000 CNY	357	1083	32.96	(30.16,35.77)	0.900	(0.748,1.083)	.264	−0.106
>20,000 CNY	328	927	35.38	(32.30, 38.47)	Ref
Underlying Disease
0	900	2553	35.25	(33.40, 37.11)	Ref
1	174	474	36.71	(32.35, 41.06)	1.084	(0.878，1.336)	.450	0.081
≥2	78	202	38.61	(33.84, 45.39)	1.195	(0.878，1.618)	.252	0.178

95% CI: 95% confidence interval.

OR: Odds ratio.

1 US dollar 7.27 Chinese yuan.

Table 4. Coverage rates of seasonal influenza vaccination among adults in Pudong New Area, Shanghai, in the 2021–22 influenza season.

Population Characteristic	Vaccinated	Total population	Vaccination rate(%)	95% CI(%)	OR	95% CI	p	β
Total	776	6088	12.75	(11.91,13.58)
Sex
Male	317	2827	11.21	(10.05, 12.38)	Ref
Female	459	3261	14.08	(12.88, 15.27)	1.283	(1.098,1.501)	.002	0.249
Living condition
Alone	26	228	11.40	(7.25, 15,56)	Ref
Living with family	750	5860	12.80	(11.94, 13.65)	1.111	(0.746,1.726)	.619	0.106
Education level
Primary school and Junior high school	89	947	9.40	(7.54,11.26)	Ref	(0.536,2.325)
High school	110	962	11.43	(9.42, 13.45）	1.253	(0.928,1.696)	.141	0.226
Bachelor’s degree	577	4179	13.81	(12.76, 14.85)	1.475	(1.148,1.913)	.029	0.389
Health status
Very good	268	2209	12.13	(10.77, 13.49)	1.946	(0.904,5.079)	.124	0.666
Good	346	2681	12.91	(11.64, 14.18)	2.069	(0.965,5.384)	.092	0.727
Normal	156	1116	13.98	(11.94, 16.02)	2.132	(0.986,5.578)	.081	0.757
Bad/Very bad	6	82	7.32	(1.56, 13.07)	Ref
Family income
<5000 CNY	99	955	10.37	(8.43, 12.30)	Ref
5000—10,000 CNY	271	2147	12.62	(11.22, 14.03)	1.142	(0.890,1.476)	.300	0.134
10,000 Yuan—20,000 CNY	221	1761	12.55	(11.00, 14.10)	1.104	(0.848,1.445)	.467	0.099
>20,000 CNY	185	1225	15.10	(13.09, 17.11)	1.338	(1.015,1.773)	.041	0.291
Underlying disease
0	686	5413	12.67	(11.79, 13.56)	Ref
1	75	571	13.13	(10.36, 15.91)	1.169	(0.891,1.514)	.249	0.156
≥2	15	104	14.42	(7.56, 21.29)	1.401	(0.766,2.397)	.244	0.338

Table 5. Coverage rates of seasonal influenza vaccination among elderly individuals in Pudong New Area, Shanghai, in the 2021–22 influenza season.

Population Characteristic	Vaccinated	Total	Vaccination rate(%)	95% CI(%)	OR	95% CI	p	β
Total	548	4684	11.70	(10.78, 12.62)
Sex
Male	258	2233	11.55	(10.23, 12.88)	Ref
Female	290	2451	11.83	(10.55, 13.11)	1.061	（0.885，1.272）	.523	0.059
Living condition
Alone	29	426	6.81	(4.41, 9.21)	Ref
Living with family	519	4258	12.19	(11.21, 13.17)	1.854	（1.272，2.806）	.002	0.618
Education level
Primary school and Junior high school	377	3318	11.36	(10.28, 12.44)	Ref
High school	111	1054	10.53	(8.68, 12.39)	0.853	（0.672，1.075）	.183	−0.159
Bachelor’s degree	60	312	19.23	(14.83, 23.63)	1.531	（1.096，2.112）	.011	0.426
Health status
Very Good	66	546	12.09	(9.34, 14.83)	2.295	（1.217，4.729）	.015	0.831
Good	227	2295	9.89	(8.67, 11.11)	1.911	（1.063，3.808）	.045	0.648
Normal	244	1650	14.79	(13.07, 16.50)	2.824	（1.579，5.602）	.001	1.038
Bad/Very bad	11	193	5.70	(2.40, 9.00)	Ref
Family income
<5000 CNY	217	2099	10.34	(9.03, 11.64)	Ref
5000—10,000 CNY	214	1904	11.24	(9.82, 12.66)	1.050	（0.853，1.292）	.645	0.049
10,000 Yuan—20,000 CNY	88	468	18.80	(15.25, 22.36)	1.805	（1.342，2.412）	P < .01	0.591
>20,000 CNY	29	213	13.62	(8.97, 18.26)	1.193	（0.758，1.821）	.430	0.176
Underlying disease
0	196	1902	10.30	(8.94, 11.67)	Ref
1	237	1951	12.15	(10.70, 13.60)	1.185	（0.965，1.458）	.106	0.170
≥2	115	831	13.84	(11.49, 16.19)	1.369	（1.051，1.778）	.019	0.314

Willingness to get vaccinated

The most important reason for children, adults and elderly individuals receiving the influenza vaccine was their belief that the influenza vaccine was effective (89.98% of children, 80.80% of adults and 93.91% of elderly individuals). Additional reasons included that the respondents believed the vaccine reduced influenza complications (51.64% of children, 41.24% of adults and 49.37% of elderly individuals) and that the vaccine was affordable and acceptable (28.03% of children, 26.29% of adults and 32.35% of elderly individuals) (Figures 2a–4a).

Figure 2. Reasons for children receiving/not receiving the influenza vaccine.

Figure 3. Reasons for adults receiving/not receiving the influenza vaccine.

Figure 4. Reasons for elderly individuals receiving/not receiving the influenza vaccine.

The main reason that adults were reluctant to vaccinate their children was their concern about side effects (21.49%), followed by their belief that their children were healthy and did not need to receive the vaccine (13.64%). The main reason that adults were reluctant to be vaccinated was that they were in good health (37.14%), followed by concerns about side effects (13.95%). The main reason that elderly individuals were reluctant to get vaccinated was that they were well enough to not be infected by the flu (30.66%), followed by concerns about side effects (23.43%) and ignorance about the availability of the flu vaccine (19.86%) (Figures 2b–4b).

Discussion

Main findings

Our study found that the influenza vaccination rate in the 2021–2022 season (17.68%) was higher than that in the 2018–2019 season (11.80%) in Pudong New Area, Shanghai.⁷ Vaccination rates increased among all age groups compared to those from the 2018–2019 survey. Herein, the vaccination rate was the highest among children (35.68%; 95% CI: 34.02%, 37.33%), followed by adults (12.75%; 95% CI: 11.91%, 13.58%) and elderly individuals (11.70%; 95% CI: 10.78%, 12.62%), consistent with our previous studies.

Vaccination rates

This study revealed higher vaccination coverage rates than pre-pandemic surveys; this difference is consistent with the results of studies that reported improvements in the public acceptance of influenza vaccination during the COVID-19 pandemic.^9,11,12 Although the rate of flu vaccination increased among Shanghai residents during the COVID-19 pandemic(17.68%,95% CI: 17.05%, 18.32%), the vaccination rate remains much lower than that in other countries and regions. These include the following: the United States: 37.44% (95% CI: 34.54–40.38); Canada: 36.91% (95% CI:30.39–43.67); the UK: 28.33% (95% CI:20.72–36.61); Australia: 25.00% (95% CI: 22.85–27.22); Japan: 32.62% (95% CI: 30.37–34.91); Hong Kong: 25.24% (95% CI: 18.79–32.28); and the overall VCR in 43 countries: 24.96% (95% CI: 23.45–26.50).¹³ Our study revealed that the vaccination rate among children (35.68%)was significantly higher than that among the other groups.¹⁴ Although children aged 6–59 months are recommended as one of the key groups for seasonal influenza vaccination in China,¹⁵ the vaccination rate of children in China is much lower than that of children in other regions in the world. For example, the VCR of children aged 5–12 years and under 5 years in the U.S. was approximately 52.6% in 2017,¹⁶ and that in Japan was 50.6% in 2012–2013.¹⁷

Moreover, elderly individuals had the lowest vaccination rate (11.70%)in this study, much lower than the rates in many other countries, such as South Korea (75.8%), Australia (70.9%), the United States (71.5%), the United Kingdom (70.8%), New Zealand (68%), Canada (60%), Ireland (59%)¹⁸ and Beijing (below 20% in the 2013–2019 flu season).¹⁹ The reason is that cities such as Beijing and Shenzhen have optimized the policies for free flu vaccination for people older than 60 years, which increased the VCR among elderly individuals.²⁰

Factors affecting the influenza vaccination rate

In the adult group, women had a higher vaccination rate than men (P < .05), revealing that sex might be an important factor. The sex differences in influenza vaccination rates may be attributed to women being more aware of health issues and general well-being.²¹ However, we found no difference between sexes among children and the elderly group (P > .05).

Family income and education level were also important factors that influenced influenza vaccination rates. Respondents with relatively higher income were more willing to be vaccinated in both the adult group and the elderly group. The results were reversed among children: families with higher monthly income were reluctant to persuade their children to receive the flu vaccine (P < .05). Many studies indicate that parents’ higher economic status and education level showed positively higher association with parents’ willingness to vaccinate their children.However a few of studies and our research shows the opposite conclusion.²² In both the adult and elderly group, the vaccination rates of the respondents with a higher education level (bachelor’s degree) were higher than those with an education level below junior high school (P < .05). The conclusion were consistent with a study conducted in the United States, which showed that lower education levels were significantly associated with hesitation about routine childhood vaccines and influenza vaccines.²³

In the elderly group, living alone was a significant factor affecting the vaccination rate. The vaccination rate was higher for elderly individuals living with family/friends than for those living alone (p < .05), which was consistent with the results of a previous study conducted in Shanghai.²⁴ The same result was found among elderly people living alone in Beijing.²⁵ Living alone can lead to reduced social contact,²⁴ making these individuals less likely to receive vaccine-related information from family or friends, which may reduce the vaccination awareness and vaccination rates of elderly individuals. Meanwhile, the attitudes of older caregivers toward vaccination may influence the willingness of older adults to get vaccinated.²⁶

In addition, respondents with underlying diseases had a higher vaccination rate than people without underlying diseases in the elderly group, which is consistent with a previous study.¹⁴ In particular, elderly individuals with two or more underlying diseases had a higher VCR than those without underlying diseases (P < .05). In contrast, there were several previous studies showing that the vaccination rate was lower among individuals with chronic respiratory diseases.²⁴ These findings indicate that the COVID-19 pandemic has changed people’s vaccination behavior, and community health education has increased knowledge about how underlying diseases are not contraindications for the influenza vaccine.²⁷

Reasons for influenza vaccination and its influencing factors

In this survey, the main reason that parents and guardians were reluctant to have their child vaccinated was concerns about side effects, family doctors did not recommend the vaccine is also an important reason. This finding is consistent with the findings of a global survey conducted in 2018–2019 ⁷and a previous study conducted in Shanghai during the COVID-19 pandemic.¹⁴ An important reason for the lack of public confidence in vaccines is that it is difficult to access information on the safety and effectiveness of vaccines and lack of vaccination experiences.^22,28 A study show that when the parents received information from healthcare providers or pediatrics, they reported more willingness to vaccinate their children.²² So it is necessary for the CDC and medical staff to play a crucial role in influenza vaccine publication.Besides the survey shows trust in governments and trust to health system were also contributing factors to improve the confidence of vaccination.²² To enhance vaccine awareness and confidence in the public, the government needs to disseminate transparent and accurate information related to vaccines to the public through various channels.^29,30

Among older people, one of the main reasons for the reluctance to be vaccinated was concerns about side effects. Influenza vaccines are generally well tolerated and safe among elderly individuals, and serious and clinically important adverse events after vaccinations are rare among this group.³¹ Besides, a lack of knowledge about the flu vaccine was also an important barrier to vaccination uptake.So it is necessary for health staffs and physicians to disseminate reliable facts and accurate information about vaccination to older adults and their caregivers²⁶ and the government should carry out sustained awareness campaigns in communities and nursing institutions to increase vaccination coverage.³² Besides, improving access to vaccines is also an important factor in increasing vaccination rates:For example, It is necessary for the government to set up temporary vaccination sites and green channels for those who have difficulty in moving, provide door-to-door vaccination, and monitor vaccination service quality in time.⁶

In addition, the affordability of vaccines is also an important factor affecting vaccination.Although people’s willingness to receive the flu vaccine has changed since the COVID-19 pandemic, China faces challenges in promoting vaccines and maintaining high vaccination rates.³² Shanghai’s influenza vaccine is a non-immunization program vaccine: residents voluntarily vaccinated at their own expense, and the price ranges from 60 to 400 CYN.¹⁴ The inclusion of influenza vaccines in the national immunization program (EPI) maybe can increase vaccination coverage rate.³³ Free vaccination policies are effective measures showed great effect in Beijing,¹⁹ Beijing government enacted a policy of free influenza vaccinations for elderly individuals (older than 60 years) in 2007, which greatly increased the VCR among the elderly population to 19.6% in 2020.¹⁹

Therefore, to reduce the health risk to the public and economic burden of influenza, China should adopt comprehensive policy measures to actively promote influenza vaccination. First, influenza vaccination policies targeting high-risk groups (especially elderly individuals and primary and secondary school students) should be added to the national immunization program and local public health plans.¹ Second, health education about the vaccine should be enhanced to promote the willingness of vaccination. Third, the joint vaccination procedures of influenza vaccines and other vaccines should be actively promoted and optimized to improve vaccine accessibility and the efficiency of immunization services.²⁸ Finally, the accessibility of influenza vaccination services, including the convenience of vaccination locations, the distribution of vaccines, and the affordability of vaccines should be optimized.

Strengths and limitations

This study is the first to examine the influenza vaccination rate and its influencing factors in Shanghai after the COVID-19 pandemic. The findings reflect the willingness of Shanghai people to receive a vaccine after the COVID-19 pandemic, and thus, this study is of great significance.

There were several limitations. First, the cross-sectional design had a risk of selection bias or recall bias when the questionnaires were completed in the general population. Second, the respondents of this survey were residents in Shanghai, which is a region with a relatively high economic level. Therefore, the results cannot be extrapolated to other regions.

Conclusions

In conclusion, although the influenza vaccination rate in Shanghai has increased since the COVID-19 pandemic, the overall influenza VCR in Shanghai, especially among elderly individuals, remains inadequate to establish an immune barrier among different populations, and the coverage lags behind that in other developed regions. People’s vaccination is mainly influenced by attitudes, knowledge, risk perception and previous vaccination behavior.³⁴ The main influencing factors were family income, education level, underlying diseases and health status in the elderly group. It is essential to improve the influenza vaccination rate in China. Efforts should be made to increase awareness of influenza vaccines according to the characteristics of different populations. Appropriate influenza vaccination strategies and programs targeting different populations need to be implemented to enhance influenza vaccine coverage, particularly among children and elderly individuals.

Author contributions

Conceptualization, C.Y. and G.S.; methodology,C.Y.; software, G.S.; validation,C.Y., L.Z., Y.W. and W.Z.; formal analysis, G.S.; investigation,C.Y.,L.Z.,Y.J.A.Z.,G.S.; data curation, G.S., Y.Q. and Y.J.; writing – original draft preparation, G.S. and L.Z; writing – review and editing, G.S., L.Z. and C.Y.; visualization,G.S.,Y.Q.,Y.J.; supervision,W.Z.,Y.W.; project administration, W.Z., H.X. and L.H.; funding acquisition, W.Z.,C.Y.and A.Z.All authors have read and agreed to the published version of the manuscript.

Patient consent

Informed consent was obtained from all subjects involved in the study.

Acknowledgments

The authors would like to acknowledge the investigation team from the 48 communities for their help with conducting this survey. We would also like to thank Dr. RuiPing Wang and Dr. Jian Xing Yu from the Chinese Center for Disease Control and Prevention for their assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, YC, upon reasonable request.

Additional information

Funding

This work was supported by the Shanghai Pudong New Area Public Health Peak Discipline “Infectious Disease” Project [PWYggf2021-01]. Chuchu Ye received funding from the Shanghai “Rising Stars of Medical Talents” Youth Medical Talents Public Health Leadership Program and Pudong New Area Health System Discipline Leader Training Program (PWRd2021-15).