Vaccine Efficacy after the First and Second Dose of Pfizer/BioNTech Vaccine

In a study published on a pre-print server, researchers report the vaccine efficacy in the Danish vaccination program. The study included 39,000 care home residents and over 3,31,000 health care workers (HCWs). The vaccine used for 99% of care home residents, and ~90% of HCWs, was the BNT162b2 (Pfizer/BioNTech) mRNA vaccine.

The researchers found that the proportion of cases among vaccinated care home residents after one dose was not significantly different from that among the unvaccinated in the same group. However, during the first week after the second dose, there were 57 cases of COVID-19 among care home residents during this period, and 52 in the HCW group. Beyond this period, there were 27 and 10 cases, respectively.

The total number of infections among care home residents after two doses of the BNT162b2 vaccine was therefore 84. Overall, there were ~1,500 cases during this period among care home residents and over 7,000 among HCWs. In comparison, there were almost 490 infections among unvaccinated care home residents and over 5,660 among unvaccinated HCWs. When evaluated at seven days following the second dose, vaccine efficacy (VE) was 52% and 46% in care home residents and in HCWs, respectively.

After this period, it went up to 64% and 90% in these groups. These results are obtained after adjusting for the effects of sex, age, and other medical conditions. The weakened immune system among the elderly is a cause for doubt about the efficacy of vaccination in this group. Here again, the VE of 64% indicates the utility of this vaccine in protecting the elderly against the severity of COVID-19.

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