How do the two approved vaccines compare?

Two mRNA vaccines have recently been granted emergency use authorization in the United States. One vaccine is produced by Pfizer and its partner BioNTech. The other is produced by Moderna. Here’s a brief summary of how the two vaccines compare.

How well do they work?

Both vaccines were very effective at preventing symptomatic COVID in the clinical trials. The Pfizer vaccine was 95% effective; in the trial they started counting cases one weeks after the second dose of the vaccine. The Moderna vaccine was 94.1% effective; in the trial they started counting cases two weeks after the second dose of the vaccine. 

Were there differences by race and ethnicity?

Both vaccines appear to work similarly well across different race and ethnicity groups.

Are they approved for young people?

The Pfizer vaccine is authorized for people aged 16 and older.  The Moderna vaccine is authorized for people aged 18 and older. 

How many doses do you need?

Both vaccines are given as a shot in the arm and both require two injections. For the Pfizer vaccine, the second shot should happen three weeks after the first. For the Moderna vaccine, the second shot should happen four weeks after the first. 

Are side effects the same?

Both vaccines somewhat commonly cause temporary reactions like redness or pain at the injection site, fatigue, headache, muscle and joint pain. There were no severe adverse events in either clinical trial.

What don’t we know?

Neither vaccine was tested in kids. And we’re not sure yet if the vaccines prevent asymptomatic cases of COVID-19. Additional research is ongoing to answer both of these questions.

Ultimately, the two authorized vaccines are very similar in their safety and efficacy profile. They work similarly well and are similarly safe. Given limited supplies at the moment, people are unlikely to be able to choose which vaccine they get.

Last update: December 21, 2020, 12:03 pm ET

Science review: JAB