In a retrospective cohort study carried out in a large integrated healthcare organization, people who were fully vaccinated with the BNT162b2 mRNA COVID-19 vaccine showed 73% overall efficacy against SARS-CoV-2 infections and 90% efficacy against coronavirus-linked hospitalizations. Researchers undertook this study for determining the overall and variant-specific efficacy of the BNT162b2 mRNA vaccine against coronavirus-linked infections and hospitalization since vaccination.

In this, electronic health records of people (≥12 years) who were members of a large integrated healthcare system were assessed. The endpoints were SARS-CoV-2 infection (defined as testing positive for COVID-19 via a polymerase chain reaction test) and coronavirus-linked hospitalizations. On the basis of hazard ratios from the adjusted Cox models, the effectiveness of calculation was done.

Out of 4920549 people assessed for eligibility, 3436957 people (median age 45 years, 52·4% female, 47·6% male) were incorporated. For fully vaccinated people, vaccine efficacy against coronavirus-linked infections and hospital admissions is shown in Table 1:

The efficacy of the vaccine against infections declined from 88% during the 1st month after full vaccination to 47% after five months. In sequenced infections, efficacy of vaccine against delta variant infections was elevated during 1^st month after complete vaccination (93%). However, after four months, it dropped to 53%.

The efficacy of the vaccine against other (non-delta) variants during the 1st month after full vaccination was also higher (97%). However, it dropped to 67% at four-five months. For all ages, the efficacy of the vaccine against coronavirus (delta variant)-related hospitalization was high (93%) up to six months.

The decline in efficacy of BNT162b2 vaccine against viral infections after some time is possibly due to decreasing immunity with time instead of the delta variant escaping vaccine protection. According to the researchers, the booster doses are likely to be required for restoring the initial huge amounts of protection witnessed early during the vaccination programme.