Humoral immune responses to the monovalent XBB.1.5-adapted BNT162b2 mRNA booster (preprint)

Continued SARS-CoV-2 evolution and immune escape necessitated the development of updated vaccines, and a monovalent vaccine incorporating the XBB.1.5 variant spike protein is currently being rolled out. Amidst the emergence of the highly mutated BA.2.86 lineage and against the backdrop of pronounced immune imprinting, it is important to characterize the antibody responses following vaccination, particularly in the elderly. Here, we show that the monovalent XBB.1.5-adapted booster vaccination substantially enhanced both binding and neutralising antibody responses against a panel of variants, including BA.2.86, in an older population with four or more previous vaccine doses. Furthermore, neutralizing antibody titers to XBB.1.5 and BA.2.86 were boosted more strongly than titers to historical variants were. Our findings thereby suggest increased vaccine induced protection against both antigenically matched variants, as well as the more distant BA.2.86 variant, and support current vaccine policies recommending a monovalent XBB.1.5 booster dose to older individuals.

Vaccine-induced correlate of protection against fatal COVID-19 in the old and frail during waves of neutralization resistant variants of concern. (preprint)

Background: To inform future preventive measures including repeated vaccinations, we have searched for a clinically useful immune correlate of protection against fatal Covid-19 among nursing homes residents. Methods: We performed repeated capillary blood sampling with analysis of S-binding IgG in an open cohort study with inclusion of nursing home residents in Sweden. We analyzed immunological and registry data collected from September 2021 with end of follow-up 31 August 2022. The study period included implementation of the 3rd and 4th mRNA monovalent vaccine doses and Omicron virus waves. Findings: A total of 3012 nursing home residents with median age 86 were enrolled. The 3rd mRNA dose elicited a 99-fold relative increase of S-binding IgG among 2606 blood-sampled individuals and corresponding increase of neutralizing antibodies. The 4th mRNA vaccine dose boosted the levels 3.8-fold. Half-life of S-binding IgG was 72 days. A total 528 residents acquired their first SARS-CoV-2 infection after the 3rd or the 4th vaccine dose and the 30-day mortality was 9.1%. We found no indication that antibodies protected against infection with Omicron, but that the risk of death was correlated to levels of S-directed IgG below the 20th percentile. In contrast, the risk plateaued at population average above lower 35th percentile of S-binding IgG. Interpretation: In the absence of neutralizing antibodies that protection from infection, quantification of S-binding IgG post vaccination may be useful to identify the most vulnerable for fatal Covid-19 among the oldest and frailest. This information is of importance for future strategies to protect vulnerable populations against neutralization resistant variants of concern. Funding: Swedish Research Council, SciLife, Knut and Alice Wallenberg Foundation and Vinnova.

Correlates of protection, viral load trajectories and symptoms in BA.1, BA.1.1 and BA.2 breakthrough infections in triple vaccinated healthcare workers (preprint)

Background Booster vaccine doses offer protection against severe COVID-19 caused by omicron but are less effective against infection. Characteristics such as serological correlates of protection, viral abundance, and clearance of omicron infection in triple vaccinated individuals are scarce. Methods We conducted a 4-week twice-weekly SARS-CoV-2 qPCR screening shortly after an mRNA vaccine booster in 368 healthcare workers. Spike-specific IgG levels and neutralization titers were determined at study start. qPCR-positive participants were sampled repeatedly for two weeks and monitored for symptoms. Result In total 81 (cumulative incidence 22%) omicron infections were detected, divided between BA.1, BA.1.1 and BA.2. Increasing post-booster antibody titers were protective against infection (p<0.05), linked to reduced viral load (p<0.01) and time to viral clearance (p<0.05). Only 10% of infected participants remained asymptomatic through the course of their infection. Viral load peaked at day 3 and live virus could be detected for up to 9 days after first PCR-positive sample. Presence of symptoms correlated to elevated viral load (p<0.0001), but despite resolution of symptoms most participants showed Ct levels <30 at day 9. No significant differences were observed for viral load and time to viral clearance between BA.1, BA.1.1 and BA.2 infected individuals. Conclusion We report a high incidence of omicron infection despite recent booster vaccination in triple vaccinated individuals. Increasing levels of vaccine-induced spike-specific WT antibodies entail increased protection against infection and reduce viral load if infected. High viral load and secretion of live virus for up to nine days may facilitate transmission in a triple vaccinated population.

Impact of SARS-CoV-2 infection on longitudinal vaccine immune responses (preprint)

Background Recent serological investigations imply waning immune responses following SARS-CoV-2 vaccination, but prior infection may impact the breadth and duration of vaccine immune responses. Methods Using longitudinally collected blood samples from the COMMUNITY study, we determined binding (WHO BAU/ml) and neutralizing antibody titers against ten SARS-CoV-2 variants over seven months following BNT162b2 in healthcare workers with (n=111) and without (n=298) confirmed prior SARS-CoV-2 infection. A smaller group with (n=47) and without (n=61) confirmed prior SARS-CoV-2 infection receiving ChAdOx1 ncov-19 was followed for three months. Results Vaccination (BNT162b2 and ChAdOx1 ncov-19) following SARS-CoV-2 infection resulted in higher wild-type BAU/ml geometric mean titers (GMTs) at all sampling time points when compared to SARS-CoV-2 naive vaccinees (all p<0.001). GMTs were 1875 BAU/ml in convalescent and 981 BAU/ml in naive BNT162b2 vaccinees 6 weeks post vaccination. 29 weeks post vaccination, GMTs had decreased to 524 BAU/ml in convalescent and 148 BAU/ml in naive vaccinees. GMT differences between convalescents and naive following ChAdOx1 ncov-19 mirrored those after BNT162b2, but the titers were considerably lower. Finally, at all time points, neutralizing antibody titers against all ten tested SARS-CoV-2 variants were at least 2 respectively 3-fold higher in SARS-CoV-2 recovered as compared to naive vaccinees following BNT162b2 and ChAdOx1 ncov-19, respectively (all p<0.001). Conclusions These findings of substantially more robust serological responses to vaccine after natural infection imply that prior infection may be taken into consideration when planning booster doses and design of current and future SARS-CoV-2 vaccine programs.

Neutralization of VOCs including Delta one year post COVID-19 or vaccine (preprint)

BackgroundSARS-CoV-2 variants, such as Alpha, Beta, Gamma and Delta, are raising concern about the efficiency of neutralizing antibodies (NAb) induced by wild-type infection or vaccines based on the wild-type spike. MethodsWe determined IgG and NAb against SARS-CoV-2 variants one year following mild wild-type infection (n=104) and two-dose regimens with BNT162b2 (BNT/BNT) (n=67), ChAdOx1 (ChAd/ChAd) (n=82), or heterologous ChAdOx1 followed by BNT162b2 (ChAd/BNT) (n=116). FindingsWild type spike IgG and NAb remained detectable in 80% (83/104) of unvaccinated participants one year post mild infection. The neutralizing capacity was similar against wild type (reference), Alpha (0.95 (0.92-0.98) and Delta 1.03 (0.95-1.11) but significantly reduced against Beta (0.54 (0.48-0.60)) and Gamma 0.51 (0.44-0.61). Similarly, BNT/BNT and ChAd/ChAd elicited sustained capacity against Alpha and Delta (1.01 (0.78-1.31) and 0.85 (0.64-1.14)) and (0.96 (0.84-1.09) and 0.82 (0.61-1.10) respectively), with reduced capacity against Beta (0.67 (0.50-0.88) and 0.53 (0.40-0.71)) and Gamma (0.12 (0.06-0.27) and 0.54 (0.37-0.80)). A similar trend was found following ChAd/BNT (0.74 (0.66-0.83) and 0.70 (0.50-0.97) against Alpha and Delta and 0.29 (0.20-0.42) and 0.13 (0.08-0.20) against Beta and Gamma). InterpretationPersistent neutralization of the wide-spread Alpha and Delta variants one year after wild-type infection may aid vaccine policy makers in low-resource settings when prioritizing vaccine supply. The reduced capacity of neutralizing Beta and Gamma strains, but not the Alpha and Delta strains following both infection and three different vaccine regimens argues for caution against Beta and Gamma-exclusive mutations in the efforts to optimize next generation SARS-CoV-2 vaccines. FundingA full list of funding bodies that contributed to this study can be found in the Acknowledgements section

Antibody Responses After a Single Dose of ChAdOx1 nCoV-19 Vaccine in Healthcare Workers Previously Infected with SARS-CoV-2 (preprint)

BackgroundRecent reports demonstrate robust serological responses to a single dose of messenger RNA (mRNA) vaccines in individuals previously infected with SARS-CoV-2. Data on immune responses following a single-dose adenovirus-vectored vaccine expressing the SARS-CoV-2 spike protein (ChAdOx1 nCoV-19) in individuals with previous SARS-CoV-2 infection are however limited, and current guidelines recommend a two-dose regime regardless of preexisting immunity. MethodsWe compared spike-specific IgG and pseudo-neutralizing spike-ACE2 blocking antibodies against SARS-CoV-2 wild type and variants B.1.1.7, B.1.351, and P1 following two doses of the mRNA vaccine BNT162b2 and a single dose of the adenovector vaccine ChAdOx1 nCoV-19 in 232 healthcare workers with and without previous COVID-19. FindingsThe post-vaccine levels of spike-specific IgG and neutralizing antibodies against the SARS-CoV-2 wild type and all three variants of concern were similar or higher in participants receiving a single dose of ChAdOx1 nCoV-19 vaccine post SARS-CoV-2 infection (both < 11 months post infection (n=37) and [≥] 11 months infection (n=46)) compared to participants who received two doses of BNT162b2 vaccine (n=149). InterpretationOur data support that a single dose ChAdOx1 nCoV-19 vaccine serves as an effective immune booster after priming with natural SARS-CoV-2 infection up to at least 11 months post infection.

Longitudinal characterization of humoral and cellular immunity in hospitalized COVID-19 patients reveal immune persistence up to 9 months after infection (preprint)

Background: Insights into early, specific humoral and cellular responses to infection with SARS-CoV-2, as well as the persistence and magnitude of resulting immune memory is important amidst the ongoing pandemic. The combination of humoral and cellular immunity will most likely contribute to protection from reinfection or severe disease. Methods: Here, we conducted a longitudinal study on hospitalized moderate and severe COVID-19 patients from the acute phase of disease into convalescence at five- and nine-months post symptom onset. Utilizing flow cytometry, serological assays as well as B cell and T cell FluoroSpot assays, we assessed the magnitude and specificity of humoral and cellular immune memory during and after human SARS-CoV-2 infection. Findings: During acute COVID-19, we observed an increase in germinal center activity, a substantial expansion of antibody-secreting cells, and the generation of SARS-CoV-2-neutralizing antibodies. Despite gradually decreasing antibody levels, we show persistent, neutralizing antibody titers as well as robust specific memory B cell responses and polyfunctional T cell responses at five- and nine-months after symptom onset in both moderate and severe COVID-19 patients. Long-term SARS-CoV-2 specific responses were marked by preferential targeting of spike over nucleocapsid protein. Conclusions: Our findings describe the initiation and, importantly, persistence of cellular and humoral SARS-CoV-2 specific immunological memory in hospitalized COVID-19 patients long after recovery, likely contributing towards protection against reinfection.

Expansion of SARS-CoV-2-specific Antibody-secreting Cells and Generation of Neutralizing Antibodies in Hospitalized COVID-19 Patients (preprint)

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in late 2019 and has since become a global pandemic. Pathogen-specific antibodies are typically a major predictor of protective immunity, yet B cell and antibody responses during COVID-19 are not fully understood. Here, we analyzed antibody-secreting cell (ASC) and antibody responses in twenty hospitalized COVID-19 patients. The patients exhibited typical symptoms of COVID-19, and presented with reduced lymphocyte numbers and increased T cell and B cell activation. Importantly, we detected an expansion of SARS-CoV-2 nucleocapsid protein-specific ASCs in all twenty COVID-19 patients using a multicolor FluoroSpot assay. Out of the 20 patients, 16 had developed SARS-CoV-2-neutralizing antibodies by the time of inclusion in the study. SARS-CoV-2-specific IgA, IgG and IgM antibody levels positively correlated with SARS-CoV-2-neutralizing antibody titers, suggesting that SARS-CoV-2-specific antibody levels may reflect the titers of neutralizing antibodies in COVID-19 patients during the acute phase of infection. Lastly, we showed that interleukin 6 (IL-6) and C-reactive protein (CRP) concentrations were higher in serum of patients who were hospitalized for longer, supporting the recent observations that IL-6 and CRP could be used to predict COVID-19 severity. Altogether, this study constitutes a detailed description of clinical and immunological parameters in twenty COVID-19 patients, with a focus on B cell and antibody responses, and provides tools to study immune responses to SARS-CoV-2 infection and vaccination.