Kinetics of vaccine-induced neutralizing antibody titers and estimated protective immunity against wild-type SARS-CoV-2 and the Delta variant: A prospective nationwide cohort study comparing three COVID-19 vaccination protocols in South Korea

Comparative duration of neutralizing responses and protections of COVID-19 vaccination and correlates of protection

The decline in neutralizing antibody (nAb) titers and vaccine efficacy /effectiveness (VE) for SARS-CoV-2 vaccines has been observed over time and when confronted with emerging variants, two factors that are hard to distinguish. Despite substantial drop in nAb titers against Omicron, VE remains high for severe cases and fatalities, raising questions about the utility of detected nAbs as a correlate of protection for COVID-19 vaccines for varying disease severity. Here, we conducted a systematic comparison of waning dynamics of nAb and VE over time and against variants with varying levels of disease severity. Using Bayesian linear regression models, we found that antigenically-shifted variants, like Omicron, could potentially lead to greater reductions in nAb titers and primary VE against mild infections than associated immunity waning observed over a 180-day period. By comparing model predicted nAb titers and VE on the same time scales, we found that VE against severe and fatal outcomes remained above 75% even when nAb titers reached the detectable limit of assays, despite strong correlations with nAb titers (spearman correlations ≥0.7) across variants over time. This finding suggested detectable nAb titers are not always sensitive enough to fully predict protection against severe disease and death from SARS-CoV-2.

Diminishing reactogenicity with preserved immunogenicity in COVID-19 vaccines: A longitudinal observation from primary to updated booster vaccine cohorts

BACKGROUND

Encouraging annual updated COVID-19 vaccinations for high-risk populations is crucial for public health. However, concerns about significant reactogenicity persist, contributing to vaccine hesitancy. To investigate evolving COVID-19 vaccine reactogenicity and immunogenicity, we conducted a longitudinal analysis across three COVID-19 vaccine cohorts.

METHODS

The Primary Vaccine Cohort, receiving wild-type (WT) 1st to 3rd doses and WT-BA.4/5 bivalent vaccine; the XBB.1.5 Monovalent Vaccine (MoV) Cohort; and the ongoing JN.1 MoV Cohort were investigated. Reactogenicity was assessed using electronic diaries for eight days, and serological responses were measured through quantitative anti-spike protein antibody (Sab) assay. Plaque reduction neutralization testing (PRNT) was performed against WT SARS-CoV-2 and vaccine-specific variants.

RESULTS

A total of 290 participants with 690 vaccine doses and 1222 sampling points was included. Total symptom scores decreased serially from the WT 1st dose to JN.1 MoV, with changes pronounced in the younger age group (< 45 years; Spearman r = -0.13, P = 0.008). Changes were not evident in the older age group (≥ 45 years) with consistently low reactogenicity. Severe reactions also steadily declined from 26.2 % (WT 1st) to 3.3 % (JN.1 MoV). Serological analysis revealed plateauing post-vaccination Sab titers with increasing pre-vaccination levels and robust PRNT responses against vaccine strains. Age negatively correlated with Sab levels after the 1st WT dose but not in subsequent doses. Multivariable analysis found no significant association between reactogenicity and immunogenicity.

CONCLUSION

The observed decline in reactogenicity, alongside sustained immunological responses, supports the safety and efficacy of annual COVID-19 booster vaccination programs.

Rapid Recovery From SARS-CoV-2 Infection Among Immunocompromised Children Despite Limited Neutralizing Antibody Response: A Virologic and Sero-Immunologic Analysis of a Single-Center Cohort

BACKGROUND

Immunocompromised (IC) pediatric patients are at increased risk of severe acute respiratory syndrome coronavirus 2 infection, but the viral kinetics and sero-immunologic response in pediatric IC patients are not fully understood.

METHODS

From April to June 2022, a prospective cohort study was conducted. IC pediatric patients hospitalized for coronavirus disease 2019 (COVID-19) were enrolled. Serial saliva swab and serum specimens were subjected to reverse transcription polymerase chain reaction assays with mutation sequencing, viral culture, anti-spike-protein, anti-nucleocapsid antibody assays, plaque reduction neutralization test (PRNT) and multiplex cytokine assays.

RESULTS

Eleven IC children were evaluated. Their COVID-19 symptoms resolved promptly (median, 2.5 days; interquartile range, 2.0-4.3). Saliva swab specimens contained lower viral loads than nasopharyngeal swabs (P = 0.008). All cases were BA.2 infection, and 45.5% tested negative within 14 days by saliva swab from symptom onset. Eight (72.7%) showed a time-dependent increase in BA.2 PRNT titers, followed by rapid waning. Multiplex cytokine assays revealed that monocyte/macrophage activation and Th₁ responses were comparable to those of non-IC adults. Activation of interleukin (IL)-1Ra and IL-6 was brief, and IL-17A was suppressed. Activated interferon (IFN)-γ and IL-18/IL-1F4 signals were observed.

CONCLUSION

IC pediatric patients rapidly recovered from COVID-19 with low viral loads. Antibody response was limited, but cytokine analysis suggested an enhanced IFN-γ- and IL-18-mediated immune response without excessive activation of inflammatory cascades. To validate our observation, immune cell-based functional studies need to be conducted among IC and non-IC children.

Impact in the humoral and cellular immune response to SARS-CoV-2 variants after primary vaccination with AZD1222/COVISHIELD protocol in healthy adults

SARS-CoV-2 emerged rapidly as a pandemic, leading to the urgent development and authorization for the use of several vaccines, with questions relating to immunogenicity in previously infected people or to virus variants. As such, we sought to determine the humoral and cellular immune response of healthy adults to distinct SARS-CoV-2 variants upon AZD1222/COVISHIELD vaccination, using chemiluminescence (CMIA), neutralizing antibody (PRNT) and analysis of activation-induced marker (AIM) by flow cytometry, respectively. We enrolled 75 volunteers, including 26 individuals previously infected with SARS-CoV-2. Our findings demonstrated that AZD1222 vaccine induced increased levels of SARS-CoV-2-specific antibodies after two-dose vaccination scheme, as detected by CMIA (mean = 49 BAU/mL to 743 BAU/mL) and PRNT (GMT = 3, 95 % CI 2-4, to 19, 11-34). After vaccination, all volunteers presented detectable antibodies by CMIA while only 64 % presented positive PRNT. Seroconversion rates were 91 % and 48 % by CMIA and 59 % by PRNT after the first and second dose, respectively. The PRNT to Delta variant demonstrated lower titers as compared to Wuhan-like and a seroconversion of 57 %. Although by CMIA all volunteers were classified as high responders, some volunteers showed no response by PRNT and AIM. In general, previously infected volunteers had higher post-vaccination antibody titers after each dose. CD4+ T cell response was generally higher than CD8+ T cells for all variants. Overall, we observed that AZD1222 vaccination induced cross-reactivity to SARS-CoV-2 variants, in both cellular and humoral responses. During volunteer follow-up, we observed that the elevated antibody titers are lasting and were incremented by the first booster. In conclusion, our findings showed that AZD1222 vaccine was able to induce a robust immune response upon primary immunization, with cross-reactivity for the Delta VOC.

Natural Boosting and the Immunogenicity of the XBB.1.5 Monovalent Vaccine in the Coronavirus Disease 2019 Endemic Era: A Longitudinal Observational Study

BACKGROUND

With the transition from the coronavirus disease 2019 (COVID-19) pandemic into endemicity, changes in group immunity and the effect of updated XBB.1.5 monovalent vaccine (MonoV) need to be investigated.

METHODS

A multicenter vaccine cohort was followed for 3 years, and the investigation period was classified into the pre-Omicron, Omicron, and endemic eras. Thirteen sampling points were assessed, including pre- and post-MonoV administration. Specimens were classified as vaccinated, molecularly or serologically diagnosed breakthrough infection (BI), natural boosting (NB), or waned.

RESULTS

A total of 327 healthcare workers contributed 2645 blood samples from March 2021 to December 2023. The log10 anti-spike protein antibody (SAb) levels, elevated by vaccination, declined linearly in the pre-Omicron era, were maintained during the Omicron era due to BIs, and increased in the endemic era (slope = 0.02, P = .02) without additional vaccination. NB cases increased significantly across the epidemiologic eras. The incidence rate ratios were 2.72 (P < .001) for Omicron/pre-Omicron and 3.39 (P < .001) for endemic/Omicron. Plaque reduction neutralization test (PRNT) titers against circulating strains (XBB.1.5 and XBB.1.9.1) in the NB group maintained previous levels, but ratios to wild-type PRNT and fold changes exhibited significantly enhanced activity. The XBB.1.5 MonoV increased PRNT by 5.8-fold against XBB.1.5 and 6.6-fold against JN.1, showing stronger enhancement against subsequent epidemic strains than the bivalent vaccine.

CONCLUSIONS

Group immunity in the COVID-19 endemic era exhibited maintained SAb levels and adjusted neutralizing activities through BI and NB. The XBB.1.5 MonoV significantly enhanced neutralizing activity against the vaccine strain and robust immunity against the subsequent epidemic JN.1 strain.

Overcoming the age-dependent SARS-CoV-2 vaccine response through hybrid immunity: analysis of humoral and cellular immunity with mass cytometry profiling

BACKGROUND

Age-dependent immune responses to coronavirus disease 2019 (COVID-19) vaccinations and breakthrough infections (BIs) in young and middle-aged individuals are unclear.

METHODS

This nationwide multicenter prospective cohort study analyzed immune responses in participants of the ChAdOx1 (ChAd)-ChAd-mRNA vaccine group using cytometry by time-of-flight, anti-spike protein antibody (Sab) and anti-nucleocapsid antibody (Nab) titers, plaque reduction neutralization tests (PRNTs), and interferon-gamma (IFN-γ) release assays at various time points.

RESULTS

We evaluated 347 participants with an average age of 38.9 ± 9.4 years (range: 21-63). There was a significant inverse correlation between age and Sab levels after the second dose (slope - 14.96, P = 0.032), and this was more pronounced after the third dose (slope - 208.9, P < 0.001). After BIs, older participants showed significantly higher Sab titers (slope 398.8, P = 0.001), reversing the age-related decline observed post-vaccination. This reversal was also observed in PRNTs against wild-type SARS-CoV-2 and the BA.1 and BA.5 variants. IFN-γ responses increased markedly after the third dose and Bis, but showed a weak positive correlation with age, without statistical significance. Immune cell profiling revealed an age-dependent decrease in the proportions of B-cell lineage cells. The proportions of naive CD4+ and CD8+ T cells were inversely correlated with age, whereas the proportions of mature T cell subsets with memory function, including memory CD4+ T, CD8+ TEM, CD8+ TEMRA, and TFH cells, increased with age.

CONCLUSIONS

Age-dependent waning of the serologic response to COVID-19 vaccines occurred even in middle-aged individuals, but was reversed after BIs. IFN-γ responses were preserved, compensating for the decrease in naive T cell populations, with an increase in memory T cell populations.

Persistent differences in the immunogenicity of the two COVID-19 primary vaccines series, modulated by booster mRNA vaccination and breakthrough infection

INTRODUCTION

The long-term impact of initial immunogenicity induced by different primary COVID-19 vaccine series remains unclear.

METHODS

A prospective cohort study was conducted at 10 tertiary hospitals in Korea from March 2021 to September 2022. Immunogenicity assessments included anti-spike protein antibody (Sab), SARS-CoV-2-specific interferon-gamma releasing assay (IGRA), and multiplex cytokine assays for spike protein-stimulated plasma. Spike proteins derived from wild-type SARS-CoV-2 and alpha variant (Spike1) and beta and gamma variant (Spike2) were utilized.

RESULTS

A total of 235 healthcare workers who had received a two-dose primary vaccine series of either ChAdOx1 or BNT162b2, followed by a third booster dose of BNT162b2 (166 in the ChAdOx1/ChAdOx1/BNT162b2 (CCB) group and 69 in the BNT162b2/BNT162b2/BNT162b2 (BBB) group, based on the vaccine series) were included. Following the primary vaccine series, the BBB group exhibited significantly higher increases in Sab levels, IGRA responses, and multiple cytokines (CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β, interleukin (IL)-1ra, IFN-γ, IL-2, IL-4, and IL-10) compared to the CCB group (all P < 0.05). One month after the third BNT162b2 booster, the CCB group showed Sab levels comparable to those of the BBB group, and both groups exhibited lower levels after six months without breakthrough infections (BIs). However, among those who experienced BA.1/2 BIs after the third booster, Sab levels increased significantly more in the BBB group than in the CCB group (P < 0.001). IGRA responses to both Spike1 and Spike2 proteins were significantly stronger in the BBB group than the CCB group after the third booster, while only the Spike2 response were higher after BIs (P = 0.007). The BBB group exhibited stronger enhancement of T-cell cytokines (IL-2, IL-4, and IL-17A) after BIs than in the CCB group (P < 0.05).

CONCLUSION

Differences in immunogenicity induced by the two primary vaccine series persisted, modulated by subsequent booster vaccinations and BIs.

Age-Related Differences in Neutralizing Antibody Responses against SARS-CoV-2 Delta and Omicron Variants in 151 SARS-CoV-2-Naïve Metropolitan Residents Boosted with BNT162b2

BACKGROUND

Although age negatively correlates with vaccine-induced immune responses, whether the vaccine-induced neutralizing effect against variants of concern (VOCs) substantially differs across age remains relatively poorly explored. In addition, the utility of commercial binding assays developed with the wild-type SARS-CoV-2 for predicting the neutralizing effect against VOCs should be revalidated.

METHODS

We analyzed 151 triple-vaccinated SARS-CoV-2-naïve individuals boosted with BNT162b2 (Pfizer-BioNTech). The study population was divided into young adults (age < 30), middle-aged adults (30 ≤ age < 60), and older adults (age ≥ 60). The plaque reduction neutralization test (PRNT) titers against Delta (B.1.617.2) and Omicron (B.1.1.529) variants were compared across age. Antibody titers measured with commercial binding assays were compared with PRNT titers.

RESULTS

Age-related decline in neutralizing titers was observed for both Delta and Omicron variants. Neutralizing titers for Omicron were lower than those against Delta in all ages. The multiple linear regression model demonstrated that duration from third dose to sample collection and vaccine types were also significant factors affecting vaccine-induced immunity along with age. The correlation between commercial binding assays and PRNT was acceptable for all age groups with the Delta variant, but relatively poor for middle-aged and older adults with the Omicron variant due to low titers.

CONCLUSIONS

This study provides insights into the age-related dynamics of vaccine-induced immunity against SARS-CoV-2 VOCs, corroborating the need for age-specific vaccination strategies in the endemic era where new variants continue to evolve. Moreover, commercial binding assays should be used cautiously when estimating neutralizing titers against VOCs, particularly Omicron.

Clinical and laboratory considerations: determining an antibody-based composite correlate of risk for reinfection with SARS-CoV-2 or severe COVID-19

Much of the global population now has some level of adaptive immunity to SARS-CoV-2 induced by exposure to the virus (natural infection), vaccination, or a combination of both (hybrid immunity). Key questions that subsequently arise relate to the duration and the level of protection an individual might expect based on their infection and vaccination history. A multi-component composite correlate of risk (CoR) could inform individuals and stakeholders about protection and aid decision making. This perspective evaluates the various elements that need to be accommodated in the development of an antibody-based composite CoR for reinfection with SARS-CoV-2 or development of severe COVID-19, including variation in exposure dose, transmission route, viral genetic variation, patient factors, and vaccination status. We provide an overview of antibody dynamics to aid exploration of the specifics of SARS-CoV-2 antibody testing. We further discuss anti-SARS-CoV-2 immunoassays, sample matrices, testing formats, frequency of sampling and the optimal time point for such sampling. While the development of a composite CoR is challenging, we provide our recommendations for each of these key areas and highlight areas that require further work to be undertaken.

Evolution of neutralizing antibodies through vaccination and breakthrough infections in the era of COVID-19 endemicity

Despite a high vaccination rate, the COVID-19 pandemic continues with immune-evading Omicron variants. The success of additional antigenic stimulation through breakthrough infection (BI) and updated vaccination in overcoming antigenic imprinting needs to be determined. Participants in a long-term follow-up cohort of healthcare worker (HCW) vaccinee were categorized according to their infection/vaccination status. Anti-SARS-CoV-2 spike/nucleocapsid protein antibodies were measured, and plaque reduction neutralization tests (PRNTs) against wild-type (WT), BA.5, BN.1, and XBB.1.5 were conducted. The neutralization activity of intravenous immunoglobulin (IVIG) products was evaluated to assess the immune status of the general population. Ninety-five HCWs were evaluated and categorized into seven groups. The WT PRNT ND50 value was highest regardless of infection/vaccination status, and groups with recent antigenic stimulation showed high PRNT titers overall. Groups with double Omicron stimulation, either by BI plus BA.4/5 bivalent vaccination or repeated BI, exhibited significantly higher BA.5 and BN.1 PRNT to WT PRNT ratios than those with single Omicron stimulation. Overall group immunity was estimated to be boosted in January 2023, reflecting the effect of the BA.4/5 bivalent booster and additional BIs, but slightly declined in June 2023. A substantial increase in the antibody concentrations of IVIG products was noticed in 2022, and recently produced IVIG products exhibited a substantial level of cross-reactive neutralizing activity against emerging variants. Neutralizing activity against emerging variants could be enhanced by repeated antigenic stimulation via BI and/or updated vaccination. Overall group immunity was elevated accordingly, and IVIG products showed substantial activity against circulating strains.

Clinical utility of quantitative immunoassays and surrogate virus neutralization tests for predicting neutralizing activity against the SARS-CoV-2 Omicron BA.1 and BA.5 variants

Developing new antibody assays for emerging SARS-CoV-2 variants is challenging. SARS-CoV-2 surrogate virus neutralization tests (sVNT) targeting Omicron BA.1 and BA.5 have been devised, but their performance needs to be validated in comparison with quantitative immunoassays. First, using 1749 PRNT-positive sera, we noticed that log-transformed optical density (OD) ratio of wild-type (WT) sVNT exhibited better titer-correlation with plaque reduction neutralization test (PRNT) than % inhibition value. Second, we tried 798 dilutional titration tests with 103 sera, but nonlinear correlation between OD ratio and antibody concentration limited titration of sVNT. Third, the titer-correlations of two sVNT kits for BA.1 and two quantitative immunoassays for WT were evaluated with BA.1 and BA.5 PRNT. All tested kits exhibited a linear correlation with PRNT titers, but the sVNT kits exhibited high false-negative rates (cPass-BA.1 kit, 45.4% for BA.1 and 44.2% for BA.5; STANDARD F-BA.1 kit, 1.9% for BA.1 and 2.2% for BA.5), while quantitative immunoassays showed 100% sensitivity. Linear mixed-effects model suggested superior titer-correlation with PRNT for quantitative immunoassays compared to sVNT kits. Taken together, the use of quantitative immunoassays for WT, rather than rapid development of new kits, would be practical for predicting neutralizing activities against emerging new variants.

Longitudinal kinetics of neutralizing antibodies against circulating SARS-CoV-2 variants and estimated level of group immunity of booster-vaccinated individuals during omicron-dominated COVID-19 outbreaks in the Republic of Korea, 2022

The coronavirus disease 2019 pandemic persisted for 3 years and is now transitioning to endemicity. We illustrated the change in group immunity induced by vaccination (monovalent vaccines) and breakthrough infections (BIs) in a healthcare worker (HCW) cohort. Five sampling points were analyzed: before the third dose and 1, 3, 5, and 8 months after the vaccination. The last two points corresponded roughly to 1 and 4 months after omicron BA.1/BA.2 BI. A semi-quantitative anti-spike binding antibody (Sab) assay and plaque reduction neutralization test (PRNT) against circulating variants were conducted. A linear regression model was utilized to deduce correlation equations. Baseline characteristics and antibody titers after the third dose were not different between 106 HCWs with or without BI (54/52). One month after the third dose, BA.1 PRNT increased with wild-type (WT), but 3 months after the third dose, it decreased more rapidly than WT PRNT. After BI, BA.1 PRNT increased robustly and waned slower than WT. A linear equation of waning kinetics was deduced between log10Sab and months, and the slope became gradual after BI. The estimated BA.5 PRNT titers at the beginning of the BA.5 outbreak were significantly higher than the BA.1 PRNT titers of the initial BA.1/BA.2 wave, which might be associated with the smaller size of the BA.5 wave. BA.1/BA.2 BI after the third dose elicited robust and broad neutralizing activity, preferentially maintaining cross-neutralizing longevity against BA.1 and BA.5. The estimated kinetics provide an overview of group immunity through the third vaccination and BA.1/BA.2 BI, correlating with the actual outbreaks. IMPORTANCE This study analyzed changes in group immunity induced by coronavirus disease 2019 (COVID-19) vaccination and BA.1/BA.2 breakthrough infections (BIs) in a healthcare worker cohort. We investigated the longitudinal kinetics of neutralizing antibodies against circulating variants and confirmed that BA.1/BA.2 BIs enhance the magnitude and durability of cross-neutralization against BA.1 and BA.5. Correlation equations between semi-quantitative anti-spike antibody and plaque reduction neutralization test titers were deduced from the measured values using a linear regression model. Based on the equations, group immunity was estimated to last up to 11 months following the third dose of the COVID-19 vaccine. The estimated group immunity suggests that the augmented immunity and flattened waning slope through BI could correlate with the overall outbreak size. Our findings could provide a better understanding to establish public health strategies against future endemicity.

Immune Response Kinetics Following a Third Heterologous BNT162b2 Booster Dose After Primary 2-Dose ChAdOx1 Vaccination in Relation to Omicron Breakthrough Infection: A Prospective Nationwide Cohort Study in South Korea

BACKGROUND

Immune responses to each vaccine must be investigated to establish effective vaccination strategies for the ongoing coronavirus disease (COVID-19) pandemic. We investigated the long-term kinetics of immune responses after heterologous booster vaccination in relation to Omicron breakthrough infection (BI).

METHODS

Our study included 373 healthcare workers who received primary ChAdOx1 vaccine doses and a third BNT162b2 vaccine dose. BIs that occurred after the third vaccine were investigated. Blood specimens were collected before and 3 months after the booster dose from participants without BI and 1, 4, and 6 months after BI from participants who experienced BI. Spike-specific binding and neutralizing antibody levels against the wild-type virus, Omicron BA.1, and Omicron BA.5, as well as cellular responses, were analyzed.

RESULTS

A total of 346 participants (82 in the no BI group; 192 in the BI group during the BA.1/BA.2 period; 72 in the BI group during the BA.5 period) were included in the analysis. Participants without BI exhibited the highest binding and neutralizing antibody concentrations and greatest cellular response 1 month after the third vaccination, which reached a nadir by the ninth month. Antibody and cellular responses in participants who experienced BI substantially increased postinfection. Neutralizing antibody titers in individuals who experienced BI during the BA.1/BA.2 period showed more robust increase against wild-type virus than against BA.1 and BA.5.

CONCLUSIONS

Our findings provide evidence of antigenic imprinting in participants who received a heterologous booster vaccination, thereby serving as a foundation for further studies on the impact of BIs on immune responses.

Effectiveness of regdanvimab treatment for SARS-CoV-2 delta variant, which exhibited decreased in vitro activity: a nationwide real-world multicenter cohort study

Background

Immune-evading severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants are emerging continuously. The clinical effectiveness of monoclonal antibody agents that exhibit decreased in vitro activity against SARS-CoV-2 variants needs to be elucidated.

Methods

A nationwide, multicenter, retrospective cohort study was designed to evaluate the effectiveness of regdanvimab, an anti-SARS-CoV-2 monoclonal antibody agent. Regdanvimab was prescribed in South Korea before and after the emergence of the delta variant, against which the in vitro activity of regdanvimab was decreased but present. Mild to moderate coronavirus 2019 (COVID-19) patients with risk factors for disease progression who were admitted within seven days of symptom onset were screened in four designated hospitals between December 2020 and September 2021. The primary outcomes, O₂ requirements and progression to severe disease within 21 days of admission, were compared between the regdanvimab and supportive care groups, with a subgroup analysis of delta variant-confirmed patients.

Results

A total of 2,214 mild to moderate COVID-19 patients were included, of whom 1,095 (49.5%) received regdanvimab treatment. In the analysis of the total cohort, significantly fewer patients in the regdanvimab group than the supportive care group required O₂ support (18.4% vs. 27.1%, P < 0.001) and progressed to severe disease (4.0% vs. 8.0%, P < 0.001). In the multivariable analysis, regdanvimab was significantly associated with a decreased risk for O₂ support (HR 0.677, 95% CI 0.561-0.816) and progression to severe disease (HR 0.489, 95% CI 0.337-0.709). Among the 939 delta-confirmed patients, O₂ support (21.5% vs. 23.5%, P = 0.526) and progression to severe disease (4.2% vs. 7.3%, P = 0.055) did not differ significantly between the regdanvimab and supportive care groups. In the multivariable analyses, regdanvimab treatment was not significantly associated with a decreased risk for O₂ support (HR 0.963, 95% CI 0.697-1.329) or progression to severe disease (HR 0.665, 95% CI 0.349-1.268) in delta-confirmed group.

Conclusions

Regdanvimab treatment effectively reduced progression to severe disease in the overall study population, but did not show significant effectiveness in the delta-confirmed patients. The effectiveness of dose increment of monoclonal antibody agents should be evaluated for variant strains exhibiting reduced susceptibility.

Neutralizing activity against Omicron BA.5 after tixagevimab/cilgavimab administration comparable to those after Omicron BA.1/BA.2 breakthrough infections

Introduction

The effect of tixagevimab/cilgavimab (Evusheld™; AstraZeneca, UK) should be evaluated in the context of concurrent outbreak situations.

Methods

For serologic investigation of tixagevimab/cilgavimab during the BA.5 outbreak period, sera of immunocompromised (IC) hosts sampled before and one month after tixagevimab/cilgavimab administration and those of healthcare workers (HCWs) sampled one month after a 3^rd shot of COVID-19 vaccines, five months after BA.1/BA.2 breakthrough infection (BI), and one month after BA.5 BI were investigated. Semi-quantitative anti-spike protein antibody (Sab) test and plaque reduction neutralizing test (PRNT) against BA.5 were performed.

Results

A total of 19 IC hosts (five received tixagevimab/cilgavimab 300 mg and 14 received 600 mg) and 41 HCWs (21 experienced BA.1/BA.2 BI and 20 experienced BA.5 BI) were evaluated. Baseline characteristics did not differ significantly between IC hosts and HCWs except for age and hypertension. Sab significantly increased after tixagevimab/cilgavimab administration (median 130.2 BAU/mL before tixagevimab/cilgavimab, 5,665.8 BAU/mL after 300 mg, and 10,217 BAU/mL after 600 mg; both P < 0.001). Sab of one month after the 3^rd shot (12,144.2 BAU/mL) or five months after BA.1/BA.2 BI (10,455.8 BAU/mL) were comparable with that of tixagevimab/cilgavimab 600 mg, while Sab of one month after BA.5 BI were significantly higher (22,216.0 BAU/mL; P < 0.001). BA.5 PRNT ND₅₀ significantly increased after tixagevimab/cilgavimab administration (median ND₅₀ 29.6 before tixagevimab/cilgavimab, 170.8 after 300 mg, and 298.5 after 600 mg; both P < 0.001). The ND₅₀ after tixagevimab/cilgavimab 600 mg was comparable to those of five months after BA.1 BI (ND₅₀ 200.9) while ND₅₀ of one month after the 3^rd shot was significantly lower (ND₅₀ 107.6; P = 0.019). The ND₅₀ of one month after BA.5 BI (ND₅₀ 1,272.5) was highest among tested groups, but statistical difference was not noticed with tixagevimab/cilgavimab 600 mg.

Conclusion

Tixagevimab/cilgavimab provided a comparable neutralizing activity against the BA.5 with a healthy adult population who were vaccinated with a 3^rd shot and experienced BA.1/BA.2 BI.