COVID-19 vaccines: Safety, side effects –– and coincidence – Harvard Health Blog

As the pandemic rages on, it’s increasingly clear that widespread vaccination is essential to help contain it. Physical distancing, universal face coverings, and frequent handwashing are effective, but not foolproof. And of course, these measures don’t work if they are not followed.

So, the rapid development of mRNA vaccines and other vaccines to prevent COVID-19 is welcome — some say miraculous — news. But while many people are scrambling to get a vaccine, others are hesitating.

Start here: Are these vaccines safe and effective?

It’s natural to wonder if brand new vaccines against a novel coronavirus, developed at unprecedented speed, are effective and safe to take. Let’s review some of what we know.

Overall effectiveness has been reported in the range of 70% to 95%. That’s well above the average effectiveness of the flu vaccine, for example.

  • A Pfizer/BioNTech vaccine trial involving nearly 44,000 volunteers found vaccination to be 95% effective. This vaccine is authorized for use in the US.
  • A Moderna vaccine trial enrolling more than 30,000 volunteers reported an effectiveness of 94%. This vaccine is authorized for use in the US.
  • An AstraZeneca/Oxford vaccine trial reported average effectiveness of 70% with full doses, but even better results (as high as 90%) with a lower dose. This vaccine is authorized for use in Great Britain, but not in the US.
  • In a press release, Johnson and Johnson announced overall effectiveness of 66% in preventing moderate to severe COVID-19. The company has applied for emergency use authorization in the US.

Not only do these vaccines appear to lessen risk of developing COVID-19, but they also appear to lessen the risk of severe disease.

What are the most common COVID vaccine side effects?

In large clinical trials, most side effects have been minor. When side effects occur, they typically last just

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