Safety and Efficacy of the Pfizer Covid-19 Vaccine
A two-dose regimen of Pfizer vaccine conferred 95% protection against Covid-19 in persons 16 years of age or older. Safety over a median of 2 months was similar to that of other viral vaccines.
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The trial report does not address
the prevention of Covid-19 in other populations, such as younger adolescents,
children, and pregnant women. Safety and immune response data from this trial
after immunization of adolescents 12 to 15 years of age will be reported
subsequently, and additional studies are planned to evaluate BNT162b2 in
pregnant women, children younger than 12 years, and those in special risk
groups, such as immunocompromised persons.
The most commonly reported side effects, which typically lasted several days, were pain at the injection site, tiredness, headache, muscle pain, chills, joint pain, and fever. Of note, more people experienced these side effects after the second dose than after the first dose, so it is important for vaccination providers and recipients to expect that there may be some side effects after either dose, but even more so after the second dose.
FDA stated the most common side effect experienced by people who received the vaccine was pain, redness or swelling at the injection site (generally the arm).
That was followed by short-term fatigue, headache and muscle-pain.
But beyond these mild effects, there was no notable difference in health conditions between the vaccinated and control groups during the study period.
Scientists will look for hidden side effects and other health issues.
In the United Kingdom, two people have had serious allergic reactions after getting Pfizer’s vaccine since its rollout December 8, prompting health officials there to recommend that people with “significant allergies” that trigger anaphylaxis not take the vaccine.
Those allergic reactions raise questions about whether the vaccine might cause very rare side effects not seen in the clinical trials. The trials, which included more than 40,000 people, found that the vaccine is safe, with side effects that include fever, chills, headache, pain at the injection site and fatigue. Those side effects tended to last for only a day or two and were generally mild to moderate.
Although such side effects could be unpleasant for some people, they are common reactions to vaccines approved for other diseases, experts say. But some side effects may come to light only once millions instead of thousands of people have been vaccinated.
A small number of people in the Pfizer trial had antibodies in their blood indicating that they had been infected prior to joining the study. Some of those people went on to develop COVID-19 during the study. That may suggest that having the disease doesn’t completely protect people from reinfection and that people who previously had COVID-19 should also get vaccinated.
Also unknown is whether previously infected people could get away with a single vaccine shot to boost their natural immunity, or if they will need two shots like everyone else.
While the trials have found the Pfizer-BioNTech vaccine to be 95 percent effective overall, there’s not enough data to show that’s true for all populations.
Pfizer has been testing its vaccine in adolescents 12 and older and Moderna began testing its vaccine in adolescents December 10. There’s not yet enough data to say how well the vaccine works for them.
No companies have tested COVID-19 vaccines in kids younger than 12. Kids tend to develop milder symptoms of COVID-19 than adults do.
As a result, trials testing effectiveness would have to be enormous if done the same way for children as in adults. Instead, vaccine makers might measure antibodies in younger vaccinated children to see whether kids have the same kinds of immune reactions to the vaccine as adults and teens.
Pregnant women and under-16s were not included in those studied, and so the vaccine will not yet be approved for these groups.
There was a fear that any COVID-19 vaccines wouldn’t work well for older or obese people, because age and obesity can both diminish immune responses, and people in both groups are at increased risk of developing severe COVID-19 or dying. But data from the Pfizer trials suggest that the vaccine works just as well in people 65 and older as it does in younger adults. Obese people were also protected at levels similar to non-obese people. Scientists will want to confirm that these groups are actually protected by the vaccine.
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