Strong peak immunogenicity but rapid antibody waning following third vaccine dose in older residents of care homes

Older people have suboptimal responses to primary series vaccines, which can place them at risk for adverse coronavirus disease 2019 outcomes. Here the authors show that booster vaccines provide a substantial increase in antibody levels in the short term but that there is significant waning 100 d after booster shots. Third-dose coronavirus disease 2019 vaccines are being deployed widely but their efficacy has not been assessed adequately in vulnerable older people who exhibit suboptimal responses after primary vaccination series. This observational study, which was carried out by the VIVALDI study based in England, looked at spike-specific immune responses in 341 staff and residents in long-term care facilities who received an mRNA vaccine following dual primary series vaccination with BNT162b2 or ChAdOx1. Third-dose vaccination strongly increased antibody responses with preferential relative enhancement in older people and was required to elicit neutralization of Omicron. Cellular immune responses were also enhanced with strong cross-reactive recognition of Omicron. However, antibody titers fell 21-78% within 100 d after vaccine and 27% of participants developed a breakthrough Omicron infection. These findings reveal strong immunogenicity of a third vaccine in one of the most vulnerable population groups and endorse an approach for widespread delivery across this population. Ongoing assessment will be required to determine the stability of immune protection.

Automated summary

Older people have suboptimal responses to primary series vaccines, but booster vaccines can increase antibody levels in the short term. However, antibody levels decline within 100 days after the booster shots and breakthrough infections can still occur. This study highlights the strong immunogenicity of a third vaccine dose in vulnerable older populations and supports widespread vaccination in this group.