How Will We Know That a COVID-19 Vaccine Is Safe?

COVID-19 vaccines have been given to tens of millions of children and hundreds of millions of adults, yet some still question their safety. Dr. Paul Offit explains what has been done to ensure that COVID-19 vaccines are — and continue to be — safe.


How will we know that a COVID-19 vaccine is safe?

Paul Offit, MD: My name is Paul Offit. I'm talking to you today for the Vaccine Education Center at the Children's Hospital of Philadelphia. I think as parents, the most important thing we care about when we give a vaccine to our children is whether or not the vaccine is safe. Above all, is it safe? And I think as a voting member on the FDA's Vaccine Advisory Committee, I can tell you that every person around that committee who are not only parents but also grandparents, have the same question. Is this safe? Have these vaccines been proven to be safe?

So, it's always a challenge. I mean, so for example, when in December of 2020 we reviewed data on vaccines, the mRNA vaccines for Pfizer and Moderna, those trials were 40,000 people big or 30,000 people, but we were making recommendations for, ultimately, hundreds of millions of people. Same thing with the vaccine recommendation for the 12- to 15-year-old, where you're making vaccine recommendations for tens of millions of children, we were looking at a trial to see whether or not the vaccine worked or was safe in about 2,400 children. Same thing for the 5- to 11-year-old, where we looked at a trial of 2,400 children, again, 1,600 of whom got vaccine, about 800 of whom got placebo, to make a decision about 28 million children.

So, was that enough? Is it enough to say that something is safe when you've tested it in 2,400 children, for example for the 5- to 11-year-old age group, and you're about to give it to 28 million children?

And I think the issue is always is not when do you know everything, you really never know everything, the question is, when do you know enough? You certainly know that this virus can cause harm. You know that this virus can cause children to suffer and be hospitalized and die, including young children. And you know that this virus is common in terms of its ability to circulate and infect.

The good news is at this point, and I'm talking to you now at the end of January of 2022, children over 5 years of age have received this vaccine in large numbers. I mean, there have been now millions and millions of children, at least 10 million children just between 5 and 11 years of age who've received the vaccine. And hundreds and hundreds of millions of people over 12 years of age who've received the vaccine. So, there are no secrets anymore. We know everything we need to know now I think about the vaccine in terms of its safety. And while the messenger RNA vaccines, or mRNA vaccines, are very, very rare cause of something called myocarditis, which is inflammation of the heart muscle, the good news is that phenomenon appears to be short-lived, transient and self-resolving. And people should also know that the virus itself can cause myocarditis and, frankly, much more severely than whatever occur following a vaccine.

So, I think parents are right to ask the question, is this vaccine safe, remembering nothing is absolutely safe. Anything in medicine that has a positive effect can have a negative effect. There are no risk-free choices, just choices to take different risks. And the job of a parent is to take the lesser risk. And in this case, the lesser risk is taking a vaccine, which although it can have this rare, transient, short-lived side effect of myocarditis, the benefits of that vaccine completely outweigh that rare risk because COVID itself can cause myocarditis, severely. COVID itself can cause myocarditis to the point that you have to go to the intensive care unit. So, it's important to know that that you choose the lesser risk, and the vaccine is always the lesser risk.

So, I think we can safely say that vaccines are safe and that they meet the definition of safe, which is that benefits clearly and definitively outweigh risks.

Related Centers and Programs: Vaccine Education Center

Last Reviewed on Feb 17, 2022