Vaccine effectiveness of the first dose of ChAdOx1 nCoV-19 and BNT162b2 against SARS-CoV-2 infection in residents of long-term care facilities in England (VIVALDI): a prospective cohort study
Study (n=10,412) found single-dose vaccination with BNT162b2 and ChAdOx1 provides substantial protection against infection in older adults from 4–7 weeks after vaccination and might reduce SARS-CoV-2 transmission, though risk of infection is not eliminated.
Source:
The Lancet Infectious Diseases
SPS commentary:
The study reported that adjusted hazard ratios (HRs) for PCR-positive infection relative to unvaccinated residents declined from 28 days after first vaccine dose to 0·44 (95% CI 0·24–0·81) at 28–34 days and 0·38 (0·19–0·77) at 35–48 days. Findings were similar for ChAdOx1 (0·32; 0·15–0·66) and BNT162b2 (0·35, 0·17–0·71) vaccines at 35–48 days.
Also published in the journal are the findings of a rest-negative, case-control study (n=466 [144 test-positive; 322 test-negative]), which found that one dose of either BNT162b2 (vaccine effectiveness [VE] 71·4%) or ChAdOx1 nCoV-19 (VE 80·4%) resulted in substantial risk reductions of COVID-19-related hospitalisation in people aged at least 80 years.
According to a commentary, in both studies, the confidence intervals for estimates of vaccine efficacy are wide, but these results provide reassurance that—in older adults (some of whom were frail and had many comorbidities)—both ChAdOx1 nCoV-19 and BNT162b2 provide protection from COVID-19 and, in cases of breakthrough infection, probably decrease the likelihood of viral transmission. It notes that results from at least 42 days after vaccination will be interesting, given the UK strategy of delaying the second dose; however, these findings will be of less direct relevance for older adults in the UK given that more than 90% of people older than 65 years have now received two doses. It concludes that these two studies give cause for optimism; despite older individuals developing decreased humoural responses to vaccines, including SARS-CoV-2 vaccine, efficacy is high, and second doses will probably increase efficacy further. Data are waited on clinical vaccine efficacy in other vulnerable groups, including those at risk of vaccine hyporesponsiveness, such as those with organ transplants or receiving immunosuppression.