Human monoclonal antibody F61 nasal spray effectively protected high-risk populations from SARS-CoV-2 variants during the COVID-19 pandemic from late 2022 to early 2023 in China

ABSTRACT

Following the national dynamic zero-COVID strategy adjustment, the utilization of broad-spectrum nasal neutralizing antibodies may offer an alternative approach to controlling the outbreak of Omicron variants between late 2022 and early 2023 in China. This study involved an investigator-initiated trial (IIT) to assess the pharmacokinetic, safety and efficacy of the F61 nasal spray. A total of 2,008 participants were randomly assigned to receive F61 nasal spray (24 mg/0.8 mL/dose) or normal saline (0.8 mL/dose) and 1336 completed the follow-up in the IIT. Minimal absorption of F61 antibody into the bloodstream was detected in individuals receiving F61 nasal spray for seven consecutive days. No treatment-emergent adverse reactions of grade 3 severity or higher were reported. In the one-dose cohort, the 7-day cumulative SARS-CoV-2 infection rate was 79.0% in the F61 group and 82.6% in the placebo group, whereas, in the multiple-dose (once daily for 7 consecutive days) cohort, the rates were 6.55% in the F61 group and 23.83% in the placebo group. The laboratory-confirmed efficacy of F61 was 3.78% (−3.74%–10.75%) in the one-dose cohort and 72.19% (57.33%–81.87%) in the multiple-dose cohort. In the real-world study, 60,225 volunteers in four different regions were administered the F61 nasal spray based on the subject's wishes, over 90% efficacy rate was observed against different Omicron variants. The F61 nasal spray, with its favourable safety profile, could be a promising prophylactic monoclonal antibody against SARS-CoV-2 VOCs.

KEYWORDS:

• SARS-CoV-2
• prophylactic protection
• monoclonal antibody
• variants of concern
• F61

Introduction

The global epidemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its variants of concern (VOCs) has persisted for over 3 years, resulting in an unprecedented public health burden and mortality rates [1–5]. The Omicron VOCs, initially detected in Southern Africa in November 2021, initially detected and became the predominant strain globally. Late in 2022, a rapidly spreading new wave of the COVID-19 pandemic in China, attributed to the emergence of Omicron variants BA.5 and BF.7, which displayed increased transmissibility and resistance to prevalent neutralizing antibodies in China, garnered significant attention [6,7]. This situation has placed substantial strain on the healthcare system [8]. Vaccination as a primary strategy for preventing and controlling COVID-19 has been well-established [9]. However, under specific circumstances or emergencies, pre-exposure and post-exposure prophylaxis of antibodies could be an effective strategy against SARS-CoV-2 and its VOCs, as it can neutralize the virus at the early stages of the infection.

By the end of 2022, several therapeutic neutralizing monoclonal antibodies (mAbs) against SARS-CoV-2 were authorized for emergency use, including those approved for clinical use, and those under investigation in clinical trials. Given that the epithelial cells of the upper respiratory tract, i.e. the nasal and oral cavities, represent the first and primary sites of SARS-CoV-2 infection [10,11]. Omicron variants have a particular affinity for the upper airways [12]. Notably, the antibody concentrations in the lungs are significantly lower than those in the serum following intravenous infusion [13,14], necessitating the administration of high mAbs doses to achieve therapeutic or prophylactic levels at the site of infection, this yields suboptimal protection against respiratory viruses [15]. The topical administration of neutralizing mAbs via the nasal mucus holds an advantage in the prevention and treatment of respiratory viruses, as demonstrated in the cases of the influenza virus and respiratory syncytial virus [16–18]. For the SARS-COV-2, Evusheld was authorized for pre-exposure prophylaxis through intranasal administration [19]. An HPMC-based mAb nasal spray solution containing IgG1 nasal fluid-neutralizing antibodies for over six hours [20]. Post-exposure prophylaxis SA58 nasal spray mAbs also showed favourable efficacy and safety in over 1000 subjects clinical study [21]. Many other prophylactic antibodies administered intranasally are in the clinical stage or have been completed clinical trials (NCT05977101, NCT05358873, NCT05765279) [22,23]. These examples indicate the feasibility of mAbs for preventing SARS-CoV-2 VOCs through intranasal administration.

Our previous research identified a neutralizing mAb, F61, isolated and screened from the peripheral blood lymphocytes (PBMCs) of convalescent patients with the infection of prototype SARS-CoV-2. F61 was selected using phage display technology. Initially, hundreds of mAbs were initially screened from the library. After a series of subsequent rounds of screening for antigen-binding activity, antigen-affinity, and neutralization activity, the mAb F61 was found to possess potent neutralization activity against SARS-CoV-2 variants both in vivo and in vitro, this antibody specifically targets and binds to the G446-S494 epitopes on the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein [24–26]. These findings demonstrate that, under appropriate screening conditions and with a sufficiently large screening pool, it is feasible to discover broad-spectrum neutralizing antibodies effective against other circulating strains, even in the convalescent patients who had been infected with the prototype strain. The production of F61 nasal spray in compliance with the Good Manufacturing Practices (GMP), and exhibiting good safety in animal models, owning the potential to be used in humans. Given the increased risk of exposure to SARS-CoV-2 VOCs, this study was conducted to assess the efficacy and safety of the F61 nasal spray in preventing infection by SARS-CoV-2 VOCs to control the potential pandemic of SARS-CoV-2 from late 2022 to early 2023.

Methods

Study design for investigator-initiated trials

This randomized, double-blind, placebo-controlled, investigator-initiated trial (IIT) was supported by the Wuhan Institute of Biological Products Co. Ltd. Three cohorts were included in this IIT. The pharmacokinetic cohort was assessed at the clinical centre of Shulan (Hangzhou) Hospital (registered under the Chinese Clinical Trial Registry, ChiCTR2200066841), which included a small sample size of participants recruited to investigate the serum antibody concentration and the safety of seven consecutive doses of F61 nasal spray. At the other clinical centre of Wuhan Jinyintan Hospital (registered under the Chinese Clinical Trial Registry, ChiCTR2200066391), a clinical trial involving thousands of participants aimed to explore the safety and efficacy of the F61 nasal spray in preventing infection in adults at risk of SARS-CoV-2 exposure in one dose (single dose of F61 nasal spray or normal saline was given) and multiple-dose (daily administration of the F61 nasal spray or normal saline for seven consecutive days) cohorts. Data monitoring and statistical analyses were conducted by an independent company. The study strictly complied with the ethical principles outlined in the Declaration of Helsinki, Good Clinical Practice (GCP), informed consent, relevant regulations, and ethical guidelines.

Participants for investigator-initiated trials

Healthy participants (18–50 years old) were enrolled in the pharmacokinetic cohort, while susceptible healthy participants over 18 years old were screened in one-dose/multiple-dose cohorts. All participants were confirmed to be free from SARS-CoV-2 infection before enrolment. Signed informed consent was obtained from all participants. The detailed exclusion and inclusion criteria are summarized in Supplementary Methods S1.

Randomization and interventions for investigator-initiated trials

For the entire IIT study, the nasal spray of recombinant whole human monoclonal antibody against SARS-CoV-2 (F61 nasal spray) was developed by the Wuhan Institute of Biological Products Co. Ltd. An independent statistician, unaffiliated with the study, was responsible for blinding clinical samples. The random allocation of the F61 nasal spray and placebo followed the PLAN procedure using software SAS (version 9.4), while the randomization number of the participants was based on block randomization. The participants were randomly assigned to the F61 (24 mg/0.8 mL/bottle) or placebo (normal saline/0.8 mL/bottle) groups (4:1 ratio in the pharmacokinetic cohort and 1:1 ratio in the one-dose/multiple-dose cohort) according to a random number assignment. All the participants and investigators remained masked throughout the trial until unblinding.

In the pharmacokinetic cohort, the subjects were treated with one bottle of F61 or normal saline once a day for seven consecutive days with each dose administered at intervals of 18–30 h. Blood samples of 4 mL were collected from each subject on day 1 within 1 h before administration (0 h) and 1, 4, and 12 h after the 1st administration; on day 3 before the 3rd administration; on day 5 before the 5th administration; on day 7 before the 7th administration and 1, 4, 12, and 24 h after the 7th administration on day 8 for the detection of F61 antibodies. The antibody detection method was established and conducted by Junke Zhengyuan (Tianjin) Biomedical Technology Co., LTD (Supplementary Methods S2).

In the one-dose/multiple-dose cohort, the participants were recruited into one-dose cohort and multiple-dose cohort. In the one-dose cohort, the individuals were given a single administration of F61 nasal spray or placebo on the first day, whereas in the multiple-dose cohort, the individuals were given multiple administrations once a day for seven consecutive days with 18–30 h intervals. Oropharyngeal swabs of all the individuals were collected before administration and 1, 2, 3, 5, 7 days after the first dose in both cohorts. The daily presence or absence of SARS-CoV-2 was determined using real-time reverse transcriptase-polymerase chain reaction (RT-qPCR) by Wuhan Kaidewei Biotechnology Co., Ltd or using the Novel Coronavirus (2019-nCoV) Nucleic Acid Diagnostic Kit (PCR-Fluorescence Probing) (Wuhan Mingde Biotechnology Co., LTD, China).

For the IITs, all participants, regardless of their SARS-CoV-2 infection status, the treatment-emergent adverse reactions (TEARs) including fever, diarrhoea, rash, vomiting, dizziness, dry eyes, dry throat, runny nose, nasal congestion, laryngeal pain, nasal mucosal dryness, nasal pruritus, and sneezing and other discomfort symptoms throughout the study were observed and recorded on the daily card during the main observation period (7 days after the first administration for the one-dose cohort and continuous 7 days for the multiple- dose cohort). The D9-D15 adverse event of multiple-dose cohort was also recorded during follow-up by telephone on day 15.

Real-world study design

Individuals aged 18 or older were recruited from four regions, including communities and medical isolation sites. Specific vulnerable populations, such as elderly residents and caregivers in nursing homes, individuals in close contact with infected individuals, and individuals undergoing home-based nucleic acid sampling, were recruited. Detailed exclusion and inclusion criteria are provided in Supplementary Methods S1. The administration of F61 nasal spray was based on the subject's willingness. F61 nasal spray treatments were administered when subjects were at risk of exposure to SARS-CoV-2. The SARS-CoV-2 infection was confirmed through qRT-PCR assays or SARS-CoV-2 rapid antigen detection tests. The SARS-CoV-2 infection data in the clinical centre were collected during 15-day observation period. After the administration of F61 nasal drops, participants were followed up by telephone on days 3 or 4 and days 7 or 8 to report any symptoms and SARS-CoV-2 test results. Safety follow-up of the subjects was conducted via telephone inquiry, and the serious adverse events were mainly recorded during this period.

Assessments

In the pharmacokinetic cohort, the primary pharmacokinetics endpoint was the serum concentration of F61 antibody and antidrug antibodies (ADAs) during the 7-day follow-up after the initial administration. The secondary endpoints of safety were the adverse events (AEs) including any laboratory-confirmed abnormal indicators confirmed during the follow-up. In the one-dose/multiple-dose cohort, the primary efficacy endpoint assessed the effectiveness of the F61 nasal spray against SARS-CoV-2 infection within one week after a single dose and continuous 7-day F61 nasal spray administrations. The superiority of the F61 nasal spray was set as the lower limit of the 95% confidence interval if the protective efficacy was greater than 30%. For the safety endpoint, any local and systemic TEARs appearing in the subjects of the IIT were monitored through spontaneous reporting by the participants and active follow-ups by the investigators. In the real-world study, the assessed real-world protection rate was the primary study endpoint based on the prevalence of PCR-confirmed or antigen-detection kit confirmed SARS-CoV-2 infection between F61-administered and untreated groups, with safety data being recorded.

Statistical analysis

The statistical software SAS (version 9.4) was used for the statistical analysis. The prevalence of SARS-CoV-2 infection in the F61 and placebo groups was calculated during the follow-up period. The Generalized Linear Models Log-Binomial model was used, with log transformation for binomially distributed data. Subsequently, relative risk(RR) (prevalence of SARS-CoV-2 in the F61 group/prevalence of SARS-CoV-2 in the placebo group) and its 95% confidence interval (CI) were calculated and converted to protective efficacy and its 95% CI. Protective efficacy was calculated using the formula: [(placebo group positivity rate – study group positivity rate) / placebo group positivity rate] * 100%. The F61 nasal spray was deemed to have superior efficacy if the lower limit of the 95% CI of protective efficacy exceeded 30%. For sample size calculation, the sample size in the pharmacokinetic cohort was not determined through statistical power calculation due to subject interest and safety considerations. In the one/multiple-dose cohort and the real-world study, the sample size was determined based on the superiority hypothesis testing of protective efficacy, assuming α =  0.025 (one-sided), power (1-β) = 0.8 for both one/multiple-dose cohorts and the real-world study, with a superiority margin of 0.7. PASS (Version 22) software was used for the calculation. Fisher's exact probability method was used to statistically compare the incidence of safety events between the F61 nasal spray and placebo groups.

Results

Characteristics of the study participants

The clinical trial was conducted from 8 December 2022, to 17 January 2023. A total of 31 individuals were randomized in a pharmacokinetic cohort, with 24 in the F61 group and 6 in the placebo group successfully completing the pharmacokinetic and safety follow-up. For the one-dose/multiple-dose cohort, 1977 subjects were selected, with 1077 subjects receiving a single dose (538 received F61 and 539 received saline). Among them, 287 subjects in the F61 group and 314 in the placebo group completed the trial. In the multiple-dose cohort, 901 subjects were selected, of which 450 received F61 and 450 received saline. In this cohort, 349 subjects in the F61 group and 356 in the placebo group completed the trial (Figure 1). The detailed demographic characteristics of the participants are provided in Table 1. There were no significant differences in age, sex, and nationality between the F61 and placebo groups in the one-dose and multiple-dose cohorts (Table 1). The mean (SD) age of participants was similar between the F61 and placebo groups in the IIT. Although there were more male participants than female participants in the pharmacokinetic cohort and the multiple-dose cohort, there was no significant difference in the gender distribution between the F61 and placebo groups. All subjects tested negative for SARS-CoV-2 by RT-qPCR before the first dose.

Figure 1. Flow diagram of the study.

Table 1. Demographic characteristics of the subjects.

Characteristics	Pharmacokinetic cohort		One-dose cohort		Multiple-dose cohort
	F61 (N = 24)	Placebo (N = 6)	F61 (N = 443)	Placebo (N = 478)	F61 (N = 440)	Placebo (N = 408)
Age, Mean (SD), y	26.4 (6.90)	28.8 (7.57)	43.7 (13.05)	43.4 (13.38)	35.1 (12.69)	34.4 (11.71)
Sex
Male, n (%)	22 (91.7%)	5 (83.3%)	218 (49.2)	237 (49.6)	266 (66.5)	288 (70.6)
Female, n (%)	2 (8.3%)	1 (16.7%)	225 (50.8)	241 (50.4)	134 (33.5)	120 (29.4)
Ethics group
Han, n (%)	21 (87.5%)	6 (100.0%)	437 (98.6)	469 (98.1)	393 (98.3)	396 (97.1)
Other, n (%)	3 (12.5%)	0 (0.0%)	6 (1.4)	9 (1.9)	7 (1.8)	12 (2.9)
RT-qPCR confirmed SARS-CoV-2 infection, n (%)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)

The participants were recruited and completed the clinical trial in the pharmacokinetic cohort, one-dose/multiple-dose cohort and real-world studies.

Pharmacokinetics of the F61 nasal spray

To evaluate the translational potential of F61, subjects were administered the F61 nasal spray once daily for seven consecutive days in the pharmacokinetic cohort. The mean F61 concentrations in the serum before the 1st, 3rd, 5th, and 7th doses, and 24 h after the 7th dose were 152.4, 1939.8, 4264.8, 6612.8, 8044.6 pg/mL, respectively, at 1, 4, and 12 h after the 1st and 7th administration, the concentrations were 175.8, 512.5, 934.5 pg/mL and 6804.1, 7601.2, 8017.5 pg/mL, respectively (Figure 2). No ADA was detected in the serum during the 7 days of laboratory examination.

Figure 2. The concentration of F61 nasal spray in serum samples of participants.

The blood collection time presented in the figure: D1, within 1h before 1st dose administration (0h), 1, 4, 12 h after 1st dose administration; D3 within 1 h before the 3rd dose administration, D5 within 1 h before the 5th dose administration, 1h before 7th dose administration of D7 (0 h) and 1, 4, 12, 24 h (D8) after 7th dose administration.

Safety

In the pharmacokinetic cohort, the incidence of TEAEs during the study period was lower in the F61 group (16; 66.67%) compared to the placebo group (5;83.33%), the incidence of treatment-related adverse events (TRAE) was 16.7% in both groups. All TRAEs were mild, with none of grade 3 severity or higher, and no participant withdrew from the trial due to TRAEs (Table 2).

Table 2. Occurrence of AEs in the pharmacokinetic cohort.

AE occurrence	F61 (N = 24), n (%)	Placebo (N = 6), n (%)
TEAE	16 (66.67%)	5 (83.33%)
TRAE	4 (16.67%)	1 (16.67%)
Grade 3 (severe) and above	0 (0.00%)	0 (0.00%)
Grade 3 (severe) and above TRAE	0 (0.00%)	0 (0.00%)
Any TEAE that causes the trial to pause or stop	0 (0.00%)	0 (0.00%)
Any TRAE that causes the trial to pause or stop	0(0.00%)	0 (0.00%)
SAE	0 (0.00%)	0 (0.00%)
SAE relevant to trials	0 (0.00%)	0 (0.00%)
TRAE resulting in withdrawal from the trial	0 (0.00%)	0 (0.00%)

Notes: *TEAEs, treatment-emergent adverse reactions, all the adverse events that that occur or worsen after medication from the initiation of the investigational drug/placebo use until the final study visit. TRAEs, post-medication adverse events that occur or worsen after medication associated with the drug under investigation, that is the TEAE related to the investigational drug. SAE, the adverse events that results in life-threatening AEs, death, inpatient hospitalization, prolongation hospitalization, disability/incapacity, a congenital anomaly.

In the one-dose/multiple-dose cohort, there was no significant difference in the incidence of TEAEs between the F61 and placebo groups following the administration of only one dose [19 (4.3%) and 18 (3.8%) in F61 and placebo groups, respectively, P = 0.7386], as well as after multiple doses [58 (14.5%) and 43 (10.5%) in F61 and placebo groups, respectively, P = 0.0902] (Figure 2). All the TEAEs in the one-dose/multiple-dose cohort mainly included naso pharyngeal discomfort (dryness of pharynx, runny nose, laryngeal pain, nasal mucosal dryness, nasal pruritus, and sneezing), ocular paresthesia, and upper respiratory tract infection (URTI) (Figure 3). The severity of TEAEs in the two groups was grade 1 or grade 2, and no serious TEAEs led to withdrawal in either the one-dose or the multiple-dose group.

Figure 3. TEAEs in the one-dose/multiple-dose cohort trial. Subjects receiving at least one dose were included in the safety analysis. The TEAEs in the F61 and placebo groups following one-dose (A) and multiple-dose (B) administration. All data were presented as cases (number to the right of the column) and percentages (column).

Protective efficacy

In the one-dose cohort, the cumulative positive rate of SARS-CoV-2 VOC within 1, 2, 3, 5, and 7 days following treatment with F61 was 14.1%, 30.0%, 53.0%, 77.9%, and 79.0%, respectively. In the placebo group, the rates were 27.7%, 51.1%, 67.8%, 83.9%, and 82.6%, respectively. The difference in the cumulative positive rate between the F61 and placebo groups decreased with an increase in the cumulative days following treatment (Figure 4(A)). In the multiple-dose cohort, the cumulative positive rate within 1, 2, 3, 5, and 7 days after treatment with F61 was 0.8%, 1.6%, 4.1%, 6.0%, and 6.55%, respectively, whereas that in the placebo group was 10.9%, 14.1%, 19.2%, 22.4%, and 23.83%, respectively (Figure 4(B)). The cumulative positive rate was significantly lower at 7 days post administration in the F61 group compared to the placebo group. For the subjects receiving only one dose, the superiority of the F61 nasal spray was only observed on the first day with a protective efficacy of 49.17% (31.17%–62.47%). No superiority was observed from second to seventh day following treatment (Figure 4(C)). For the multiple-dose administration cohort, the superiority of the F61 nasal spray was confirmed with a protective efficacy (95% CI) of 72.19% (57.33%–81.87%) (Figure 4(D)). These results indicate that each administration of the F61 nasal spray could provide protection against SARS-CoV2 infection, particularly against the circulating BA.5.2.X and BF.7 strains.

Figure 4. The cumulative positive rate and protective efficacy of the F61 nasal spray. The cumulative positive rate in the F61 and placebo groups following administration of one dose (A) and multiple doses (B). The protective efficacy of the F61 nasal spray following administration of one dose (C) and multiple doses (D). Protective efficacy was defined as [(positive rate in the placebo group – positive rate in the study group)/positive rate in the placebo group]*100%, with the superiority of the F61 nasal spray established if the lower limit of protective efficacy of the F61 nasal spray against SARS-CoV-2 infection after single and multiple nasal spray administrations was greater than 30%.

From regions 1, 2, 3, and 4, a total of 12,155, 997, 4620, and 42,453 participants were recruited, respectively. The infection rates in individuals aged 18 years and older in the F61 and untreated control groups in regions 1, 2, 3, and 4 were 2.8% vs 30.63%, 0.17% vs 1.99%, 1.72% vs 20.3%, and 0.11% vs 2.42%, respectively. The efficacy of the F61 nasal spray against laboratory-confirmed infections relative to the untreated control group in regions 1, 2, 3, and 4 was 91.46%, 90.86%, 91.52%, and 95.45%, respectively, during the Omicron epidemic (Table 3).

Table 3. Efficacy of the F61 nasal spray against SARS-CoV-2 VOCs in four regions.

Region (n)	Positive case in F61 group (n,n)	Positive case in untreated group%(n,n)	Efficacy(%)	Epidemic strains
R1(12155)	176(6295)	1795(5860)	91.46	BA.5.2.48>BF.7.14>BA.5.2
R2(997)	1(594)	8(403)	90.86	BA.5.2.48>BA.5.2.76>BA.5.2.49
R3 (4620)	39(2266)	478(2354)	91.52	BF.7.14>BA.5.2.48>BF.7
R4 (42453)	5(4453)	920(38000)	95.45	BA.5.2.48>BF.7.14>BA.5.2.49

Note: The epidemic strains of SARS-CoV-2 VOCs in different regions from December 1, 2022, to January 20, 2023 were acquired from the Chinese Center for Disease Control and Prevention [27].

Discussion

The broad-spectrum neutralizing mAb F61 nasal spray showed a protective efficacy of 72.19% in the IIT and over 90% in a real-world study against the infections caused by the circulating strains of SARS-CoV-2, including BF.7.14, BA.5.2.48 [28]. All AEs associated with F61 nasal spray were of mild to moderate intensity, demonstrating satisfactory safety. The F61 nasal spray is considered for use when subjects were at risk of exposure to SARS-CoV-2 VOCs.

The respiratory tract and the lung are the primary sites for the contact and binding of SARS-CoV-2. Neutralizing antibodies in the nasal mucosa provide the first barrier to SARS-CoV-2 [29]. The effectiveness of mAbs in blocking SARS-CoV-2 invasion has been demonstrated in animal models [13, 30, 31], F61 exhibits broad neutralizing activity against VOC strains (Delta, Omicron BA.1, Omicron BA.1.1, and Omicron BA.2), providing highly effective protection in vivo with dose-sparing; thus, paving the way for its use as a universal antibody against SARS-CoV-2 mutants in humans [24, 26]. Few studies have reported the pharmacokinetics of nasal mucosal immunization in the blood, our study revealed low serum antibody concentrations (in the picogram range) of F61 after seven days of repeated nasal mucosal administration. The main reason may be that F61, as a macromolecular mAb without adjuvants or delivery systems, making it less absorbable into the blood, F61 owns a long half-life but with a short detection period [32]. This also indicates that intranasally administered F61 is better concentrated on targeting the site of virus replication in the respiratory tract. No ADAs of F61 were observed in the serum, likely due to the minimal levels of F61 present in the serum.

All participants selected for the clinical study tested negative for SARS-CoV-2 by RT-qPCR. The systemic, local, and laboratory-confirmed AEs in the pharmacokinetic cohort demonstrated the safety of F61 in a small sample size. In the one-dose/multiple-dose cohort, the AEs of F61 were well-tolerated compared to the placebo. Although some individuals were still infected with VOCs, the overall AEs were fewer and milder than those reported in clinical studies involving therapeutic antibodies [33,34]. Compared with other prophylactic mAbs, F61 provided better or comparable safety and protective efficacy [21,35].

As F61 adheres to the nasal mucosa, its level in the nasal mucosa could decrease and be cleared due to rhinorrhea. Hence, multiple-dose administration is necessary when individuals are continuously at risk of exposure. This is supported by the protective efficacy of F61, which significantly decreases after a single dose over time but remains consistently high with continuous administration (Figure 4(C, D)). Some antiviral drugs are administered nasally to increase protection; for example, natural virucidal agents with a patented system (the prophylactic nasal spray) at three doses daily (6–8 h intervals) for 45 days displayed 71% efficacy in preventing SARS-CoV-2 infection [36]. Another clinical trial involving iota-Carrageenan (I-C), a sulphated polysaccharide antiviral activity, reported some protection following four-time daily intranasal administration [37]. In contrast, our study demonstrates a protective efficacy of 72.19% following daily administration under post-exposure or persistent pre-exposure conditions, which is significantly higher than the superiority threshold of 30%. The efficacy results align with those reported in previously animal models [25,26].

A large population sample study revealed over 90% protective efficacy of the F61 nasal spray, reaffirming the current application strategy for the F61 nasal spray: before you are at risk of exposure to SARS-CoV-2 VOCs, the use of F61 nasal spray in advance could effectively neutralize the SARS-CoV-2 VOCs in the respiratory tract and block the invasion. During the conduction of the one-dose cohort, there was a sudden surge in SARS-CoV-2 VOCs infections in China, and during the conduction of the multiple-dose cohort, the number of infections gradually declined [27]. This explains why the infection rates in the multiple-dose cohort, were significantly lower compared with that in the one-dose cohort, even though in the placebo subgroup. The varying protective efficacy of the F61 nasal spray in the IIT and the real-world study is mainly related to the fact that some individuals in the IIT were under post-exposure to SARS-CoV-2 VOCs, whereas most individuals in the real-world study were pre-exposed to SARS-CoV-2 VOCs.

This study has several limitations. First, the half-life period of F61 in the nasal mucosa was not studied due to the short duration of the clinical study. Second, the study only included healthy individuals over 18 years old, excluding younger populations. Third, it was challenging to distinguish medication-induced AEs from post-infection manifestations. Fourth, the analysis of the infection rate and protective efficacy only covered 7 days, lacking a longer-term evaluation of F61's safety and protective effects (e.g. over 1 month). Fifth, in the one-dose cohort, many participants declined follow-up qRT-PCR testing, leading to poor compliance. Sixth, the effective protective effect of F61 relies on daily administration, which may increase costs in practical applications. Therefore, the use of F61 is primarily intended for individuals with specific needs or in particular scenarios. such as healthcare workers at high risk of SARS-CoV-2 VOCs exposure, elderly or immunocompromised individuals travelling long distances, and people spending prolonged periods in crowded and confined spaces. Nevertheless, this study offers some advantages as it is a comprehensive clinical research that includes a pharmacokinetics study, an investigator-initiated safety and efficacy study, and a real-world study. In comparison to intravenous administration, intranasal administration seems to have a better safety profile and directly neutralizes the virus in the first line of defense. The F61 nasal spray can provide preventive protection to individuals who may not be recommended for vaccination or who do not generate a sufficient immune response after vaccination.

The clinical trial suggests that antibodies neutralizing SARS-CoV-2, such as F61, are potentially promising candidates for the treatment of viral infections in the nasal mucosa, with satisfactory safety. Thus, they may be used as candidate antibody preparations to significantly reduce the risk of laboratory-confirmed COVID-19 infections, especially in high-risk situations.

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: J.Y.Z., K.D., Y.B.P., X.X.N., X.Y., W.C., Q.L.L., F.G., C.W., Z.F.J., Z.J.W., Z.Y.Z., are employees of Wuhan Institute of Biological Products Co. Ltd., the company developed the antibody and sponsored the trial. X.M.Y., Y.K.Y., F.G.L., are employees of the China National Biotec Group Company Limited, which is the parent company of Wuhan Institute of Biological Products Co. Ltd., All other authors declare no competing interest.

Acknowledgements

We thank the trial participants, and all investigators, statistician involved in this trial. X.M.Y., M.F.L., K.D., C.L.H., initiated, coordinated, conceived, and designed the project and approved the final version of the manuscript. X.X.N., Q.L.Y., J.Y.Z., wrote the draft manuscript and revision. Y.L., W.L., S.N.R., Y.B.P., X.Y., W.C., Q.L.L., F.G., C.W., S.Z.W., L.N.S, Z.F.J., Z.Y.Z., Y.K.Y., F.G.L., W.J.W., took responsibility for the recruitment, follow-up, and data collection. M.F.L took responsibility for the integrity and the accuracy of the data analysis. X.M.Y., and K.D., provided administrative, technical, or material support.

Additional information

Funding

The current research was supported by the National Key Research & Development programme of China: Develop ment of Recombinant Human Broad-Spectrum Monoclonal Antibody Drugs against COVID-19 (2022YFC0869300), and Wuhan Science and Technology Bureau: Clinical Study and Transformation of Recombinant Human Broad-spectrum Monoclonal Antibody against COVID-19 (2022033403015181).