SARS-CoV-2 neutralising antibody activity in a highly vaccinated population: Longitudinal serology studies in Singapore

BackgroundThere is continuing uncertainty regarding the longevity of immunological responses to both SARS-CoV-2 natural infection and COVID-19 vaccines. MethodsWe analysed data from two serological cohorts in Singapore among residents of a COVID-19 affected migrant worker dormitory between May-July 2020, and among mRNA COVID-19 vaccine recipients between May 2021 and January 2022. We compared SARS-CoV-2 neutralising antibody levels by age group, sex, presence of pre-existing medical conditions, type of mRNA vaccine received and number of doses received. We investigated the effect of time since infection or vaccination on antibody levels in naturally infected individuals and two- and three-dose vaccinees. ResultsAfter two vaccine doses, neutralising antibody responses were higher in Spikevax (Moderna) recipients, females, younger individuals and those with no underlying medical conditions. However, antibody levels waned to similar levels in all groups over time. A third dose boosted these to similarly high levels in all groups. Waning was apparent among two-dose but not three-dose recipients over a period of six months. Both two and three-dose vaccine recipients showed consistently higher neutralising antibody levels compared with naturally infected individuals over the 12-week period following infection or vaccination. ConclusionsOur findings support the broad use of booster doses to improve population protection from COVID-19. However, recent increases in transmission of new SARS-CoV-2 variants, even in the presence of high levels of neutralising antibody in a highly vaccinated population, point to vaccine breakthrough as an important mechanism for maintaining SARS-CoV-2 circulation and indicate the need for variant-specific or universal COVID-19 vaccines. SummaryYounger individuals, females and those with no pre-existing conditions have higher neutralising antibody levels after two doses of COVID-19 mRNA vaccine. Subsequently these wane to levels seen in other groups. A booster dose promotes similarly high levels in all groups.