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Booster shots for all vaccines

September 30, 2021

The Centers for Disease Control and Prevention (CDC) has been promoting booster shots most recently for all vaccines for COVID-19: Pfizer, Moderna, and Johnson & Johnson.  However, the Food & Druge Administration (FDA) has only reviewed the data on the Pfizer vaccine for boosters thus far from the data which Pfizer submitted to them from their clinical trial participants.  The FDA came up with certain guidance after reviewing their data.  Meanwhile, the FDA has not granted any similar approvals for Moderna of Johnson & Johnson vaccines against COVID-19.  However, the CDC is pushing the use of boosters for all these vaccines as well.

In terms of the review of data by the FDA, they reviewed data from the United States studies conducted by Pfizer as well as several international sources like Israel who have produced a lot of studies about vaccine efficacy and they also reviewed data from the United Kingdom.  They said in their press release the following: “The immune responses of approximately 200 participants 18 through 55 years of age who received a single booster dose approximately six months after their second dose were assessed. The antibody response against SARS-CoV-2 virus one month after a booster dose of the vaccine compared to the response one month after the two-dose primary series in the same individuals demonstrated a booster response.”  In terms of statistics, what was the comparison here and how was it assessed.  I have not been able to find out.

They then followed this up by showing efficacy against the delta variant among the clinical trial participants.  They found out the following:  “The analysis submitted by the company showed that during the study period of July and August 2021, the incidence of COVID-19 was higher among the participants who completed their primary vaccine series earlier, compared to participants who completed it later. The FDA determined that the rate of breakthrough COVID-19 reported during this time period translates to a modest decrease in the efficacy of the vaccine among those vaccinated earlier.”

This is also hard to know.  They say they compared the rates of COVID-19 accrued during the delta variant surge amongst clinical trial subjects to those who also completed a two dose series, but later in the study and they found the incidence was higher for the those who had their primary series earlier. Without knowing how they analyzed this, it is somewhat hard to comment on what risk factors they might have tried to control for in their analyses, but one thing that stands out is these are different groups of individuals and the heterogeneity alone can affect the results. Also, per the results about the breakthrough infections, we are unaware how to interpret modest decrease in the efficacy and would be interested to understand the confidence intervals around these efficacy rates.  Perhaps more details will come out in the future to be able to make more statistical determination about the FDA analyses of the Pfizer vaccine or other vaccines they review for boosters.

written by,

Usha Govindarajulu



COVID-19, vaccines, boosters, efficacy, Pfizer, statistics, FDA, Usha Govindarajulu