Preprint Data: Pfizer Vaccine Shows Reduced COVID-19 Risk After 2 Weeks Administration
The to-be-reviewed assessment of real-world vaccine recipients suggests 51% greater efficacy with BNT162b2 after 13-24 days.
New data from an unreviewed, preprint research article indicates first-dose immunization efficacy from Pfizer-BioNTech coronavirus 2019 (COVID-19) vaccine BNT162b2 is improved 51% after 13-24 days among Israel residents given the vaccine.
The retrospective cohort assessment, pending review and publication, is among the first real-world indications of first-dose efficacy of the currently authorized mRNA vaccines for the pandemic.
Israel is currently the most vaccinated country against COVID-19, per capita, worldwide. According to Our World in Data, more than one-third of the total population has received at least 1 COVID-19 vaccine dose as of Thursday—or, nearly 3 million people.
Off the strength of phase 3 results for BNT162b2—which was used to support its approved Emergency Use Authorization (EUA) under the US Food and Drug Administration (FDA) last month, and showed COVID-19 prevention efficacy of greater than 90% among adults after their second dose—the current understanding is that the Pfizer-BioNTech product is among the most promising prophylaxes for the pandemic virus.
That said, investigators wrote, real-life vaccine effectiveness evaluation during the rollout phase is “urgently needed, especially given the global disease surge.”
The investigators from Maccabi Healthcare Services and Tel Aviv University sought to assess the short-term efficacy of first-dose BNT162b2 against SARS-CoV-2 infection. They hypothesized that cumulative incidence of infection among those administered vaccines would decline in the 12 days following immunization, versus incidence in the days immediately following immunization.
The retrospective cohort study used data from a 2.6 million-member health provider in the country, consisting of persons aged 16 years or older vaccinated with the Pfizer product from December 19, 2020 to January 15, 2021.
Medical history and PCR SARS-CoV-2 test results were collected from the period immediately following immunization to January 17. The team then compared cumulative infection rates in days 1-12 to days 13-24 following first dose, using Kaplan Meier survival analysis and linear models.
Overall, the assessment included 503,875 vaccinated persons. Mean patient age was 59.7 years, with 47.8% being male. A majority (69.4%) had 13-24 days follow-up.
Cumulative SARS-CoV-2 infection incidence was 0.57% during days 1-12 post-vaccination, and 0.27% in days 13-24. Investigated calculated a daily mean incidence of 43.41 infections per 100,000 in days 1-12, versus 21.08 infections per 100,000 in days 13-24. This indicated a relative risk (RR) reduction of 51.4% in the later days after vaccination.
In assessing relative RRs for persons aged 60 years and older (44.5%), younger persons (50.2%), females (50.0%), and males (52.1%), investigators observed consistent improvements in prevention against infection after 12 days.
As such—at a time when vaccine rollout and administration is escalating—the Israel-based investigators from the to-be-published analysis concluded that the very first available COVID-19 vaccine is associated with greater efficacy beyond the first 2 weeks after immunization.
“Immunization with the second dose should be continued to attain the anticipated protection,” they wrote.
