In this episode, I’ll discuss the available safety and efficacy data of Pfizer’s Covid-19 vaccine.
On December 11, 2020 the FDA granted an emergency use authorization for Pfizer’s Covid-19 vaccine.
A fact sheet for the vaccine is available from the FDA here.
Data from the trial used to support the FDA’s decision was made available in the New England Journal of Medicine on December 10, 2020.
The trial, which is still ongoing, is a multinational, placebo-controlled, observer-blinded trial. 43,548 patients were divided evenly between the vaccine and placebo groups. There were 8 cases of Covid-19 with onset at least 7 days after the second dose among participants assigned to receive the vaccine and 162 cases among those assigned to placebo. The vaccine overall was 95% effective. Similar vaccine efficacy (generally 90 to 100%) was observed across subgroups defined by age, sex, race, ethnicity, baseline body-mass index, and the presence of coexisting conditions.
Among 10 cases of severe Covid-19 with onset after the first dose, 9 occurred in placebo recipients and 1 in a vaccine recipient.
2 vaccine recipients and 4 placebo recipients died, the cause of which was judged to be unrelated to the study. There were no covid-19 related deaths in either group.
mRNA vaccines are known for their high incidence of side effects related to systemic reactivity, and this vaccine appears no different.
The trial reports side effects differently for patients under 55 and those over 55. Injection pain was reported in over 2/3 of patients and fatigue and headache in over half. There were also very high rates of fatigue and headache reported in the placebo groups, although these were well under half of the number in the vaccine group.
The most interesting side effect is fever above 38 degrees C. This was more common after the 2nd dose at 16% in younger recipients and 11% in older patients.
An editorial that accompanies this study in the journal generally offers praise for the results but highlights some significant questions that remain such as:
What happens to the inevitable large number of recipients who miss their second dose? How long will the vaccine remain effective? Does the vaccine prevent asymptomatic disease and limit transmission? And what about the groups of people who were not represented in this trial, such as children, pregnant women, and immunocompromised patients of various sorts?
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