Vaccine-induced correlate of protection against fatal COVID-19 in older and frail adults during waves of neutralization-resistant variants of concern: an observational study

Protective effect and molecular mechanisms of human non-neutralizing cross-reactive spike antibodies elicited by SARS-CoV-2 mRNA vaccination

Neutralizing antibodies correlate with protection against SARS-CoV-2. Recent studies, however, show that binding antibody titers, in the absence of robust neutralizing activity, also correlate with protection from disease progression. Non-neutralizing antibodies cannot directly protect from infection but may recruit effector cells thus contribute to the clearance of infected cells. Also, they often bind conserved epitopes across multiple variants. We characterized 42 human mAbs from COVID-19 vaccinated individuals. Most of these antibodies exhibited no neutralizing activity in vitro but several non-neutralizing antibodies protected against lethal challenge with SARS-CoV-2 in different animal models. A subset of those mAbs showed a clear dependence on Fc-mediated effector functions. We determined the structures of three non-neutralizing antibodies with two targeting the RBD, and one that targeting the SD1 region. Our data confirms the real-world observation in humans that non-neutralizing antibodies to SARS-CoV-2 can be protective.

Longitudinal changes in antibody titers in a nursing home in which COVID-19 clusters occurred

BACKGROUND

Many outbreaks of coronavirus disease 2019 have occurred in Japanese nursing homes in which residents and staff are in close daily contact. This study evaluated longitudinal changes in antibody titers in nursing homes in which clusters occurred and examined the association between antibody titer and the severe acute respiratory syndrome coronavirus 2 infection or severity.

METHODS

This cohort study included 171 participants who had provided at least one antibody titer test between June 2022 and March 2023. A descriptive analysis estimated the association between the risk of infection and antibody titer level.

RESULTS

The facility experienced 2 clusters during the study period that involved facility staff as the initial source of infection. Noninfected participants had less variation in antibody titer levels and a higher level of preinfection antibodies than infected participants. The risk of infection and severity was lower in participants with higher antibody titers than in those with lower titers.

CONCLUSIONS

We showed the changes in antibody titers over time and the association between antibody titer and severe acute respiratory syndrome coronavirus 2 infection or severity. Vaccination schedules may need to be tailored to the dynamics of decreasing antibody titers over time and the occurrence of infectious diseases in facilities.

The post-COVID-19 population has a high prevalence of cross-reactive antibodies to spikes from all Orthocoronavirinae genera

IMPORTANCE

As demonstrated by severe acute respiratory syndrome coronavirus 2, coronaviruses pose a significant pandemic threat. Here, we show that coronavirus disease 2019 mRNA vaccination can induce significant levels of cross-reactive antibodies against diverse coronavirus spike proteins. While these antibodies are binding antibodies that likely have little neutralization capacity and while their contribution to cross-protection is unclear, it is possible that they may play a role in protection from progression to severe disease with novel coronaviruses.

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.