Researchers working as part of the VIVALDI study have shed further light on the pattern of protection given to residents of long-term care facilities by COVID-19 booster doses.
Residents and staff of long-term care facilities were prioritised for COVID-19 vaccination from December 2020 and for additional rounds of vaccination from September 2021, March 2022 and September 2022.
The VIVALDI study previously showed waning of protection against infection and severe illness following a primary course of vaccination in this group from 12 weeks following a second dose. They saw an improvement in protection against severe illness following a first booster dose, which remained after the emergence of the Omicron variant.
In this new study, the research team aimed to assess the effectiveness of third, fourth and fifth booster doses death from COVID-19 among residents of long-term care facilities in England during 2022.
13,407 residents from 327 facilities were included in the study. 3,411 had previously been infected with COVID-19. 12,072 residents had received a third-dose booster dose prior to the analysis period, which rose to 13,104 by the end of the period. Fourth-dose boosters had been received by 10,846 and fifth-dose boosters by 7,311 by the end of the analysis period.
The results, published as a preprint in MedRxiv (and therefore not yet peer reviewed) found that each booster provided additional protection (relative to primary vaccination), however there was a consistent pattern of waning over time, which appeared to stabilise beyond 16 weeks at a level providing 45-75% reduction in risk.
In participants without known prior COVID-19 infection, the protection against death from COVID-19 was seen to wane from 16 weeks. A similar pattern was observed following fourth and fifth dose vaccination.
Participants with confirmed prior infection were at reduced risk of death compared to those without prior infection. Within this group, the pattern of additional protection given by booster vaccination was similar to those without known prior infection.
The researchers noted that it was possible that the (primarily) bivalent fifth-dose vaccination provided some additional long-term protection, but that the pattern of waning over time did not differ substantially from that observed for prior booster doses.