Why comparing Covid-19 vaccine efficacy numbers can be misleading

The best Covid-19 vaccine for you is most likely still the first one you can get.


Three different Covid-19 vaccines are now being distributed across the United States, and all three are highly effective at the most important thing: preventing hospitalizations and deaths from Covid-19. But some people remain worried that Johnson & Johnson’s vaccine is less effective at preventing disease to begin with.

Detroit Mayor Mike Duggan this week turned down 6,200 Johnson & Johnson vaccine doses for his city. “Johnson & Johnson is a very good vaccine. Moderna and Pfizer are the best,” Duggan said in a news conference. “And I am going to do everything I can to make sure that residents of the city of Detroit get the best.”

Scientists say that this is the wrong way to think about Covid-19 vaccines, and that judging the Johnson & Johnson vaccine as inferior based on its lower reported efficacy is misleading.

Such actions are especially worrying at the current stage of the pandemic. Covid-19 has killed more than 500,000 Americans, and while cases seem to be declining, the virus is still spreading, new variants are gaining ground, and some parts of the country are already relaxing precautions (which health officials warn could end up prolonging the pandemic).

Turning down vaccine doses while supplies of all Covid-19 vaccines are still stretched thin undermines the campaign to curb the pandemic.

In clinical trials, the vaccines produced by Pfizer/BioNTech, by Moderna, and by Johnson & Johnson reduced the fatality rate of Covid-19 by 100 percent compared to their placebo groups. They also kept all recipients out of the hospital. That means they can potentially downgrade Covid-19 from a public health crisis to a manageable problem.

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