Vaccines for COVID-19 are in the news these days. For many pediatricians and preventive medicine specialists, vaccines have always been one of their most important tools and one of their most trusted measures for keeping patients healthy. In this Q&A, Kristin Oliver, MD, MHS, a pediatrician and preventive medicine physician at the Mount Sinai Health System and an Assistant Professor of Pediatrics, and Environmental Medicine and Public Health, at the Icahn School of Medicine at Mount Sinai, explains why.

Why are vaccines so important?

Vaccines are one of the best tools we have to prevent disease and death in both children and adults. Getting vaccinated is one of the easiest things that we can do to keep ourselves and our children healthy. When I think about all the things I do to stay healthy—eat well, exercise, manage stress—that’s a lot of work. But it’s easy for me to go and get my flu shot, or bring my kids in to get their vaccines. And when I do that, I’m preventing disease, not just in myself and my family, but also in the communities where I live and work.

How do you measure the effectiveness of a vaccine?

There are two measures of how well a vaccine works. One is called “efficacy,” and that’s how well a vaccine works in a clinical trial. That’s a perfect situation where everybody in the trial who is getting the vaccine doses is getting them exactly when they’re supposed to, and they’re being watched really carefully. Later on, we look at “effectiveness.” That’s in the real world—what happens when people get that second dose a little bit late, or things aren’t in such a controlled setting? For both measures, we compare a group of people who got the vaccine to a group of people who did not get the vaccine, and see how many cases of the disease are in one group compared to the other. You hope that there’s a lot less disease in the group of patients who got the vaccine.

In general, how effective are vaccines?

When you get a disease, how long you have protection from getting it again can vary from person to person and from disease to disease. In the same way, how well a vaccine works also varies depending on the disease and the vaccine. Some vaccines have a really high efficacy rate.  For instance the MMR vaccine that protects against measles has 98 to 99 percent efficacy. Other vaccines are not quite as high. The pertussis (whooping cough) vaccine is closer to 80 to 90 percent. The flu vaccine effectiveness varies from year to year, and is closer to 50 percent. Obviously higher is better. We’re hoping that for COVID-19, vaccine efficacy and effectiveness are closer to 90 percent. But we know that’s not always realistic for every vaccine.

Do we know if the COVID-19 vaccine will be effective for the general population, including children and the elderly?

Right now, we still don’t have a complete answer. Early data from some of the clinical trials looks good. As far as children are concerned, the youngest who have started to receive the trial vaccines are 12. We don’t have enough data yet to know how well the vaccine is going to work in these groups.

If I received the COVID-19 vaccine, can I stop wearing a face mask and social distancing?

Not yet. We don’t know how effective the vaccine is going to be, or how many people are going to receive it.  The recommendation is continue to practice social distancing, wear a face mask, and really good hand-washing. We’re going to have to do this for a little while longer.

How long does a vaccine protect you from a disease?

The protection that you get from a disease, either by having the disease itself and recovering, or by getting the protection from the vaccine, is what we call immunity. This protection depends a lot on the type of disease, and the type of vaccine. Unfortunately, right now, we don’t know how long immunity lasts when you get the disease or when you get the vaccine.

Will a vaccine for COVID-19 get us closer to herd immunity for the virus?

It will definitely get us closer. Immunity is the protection you get either from having the disease, or from getting vaccinated against the disease. With herd immunity, enough people in the community have this protection so that even if someone gets the disease, it is not likely to spread widely. At that point even people who aren’t immune won’t catch it. Right now, we still don’t know what percentage of immunity we need to reach herd immunity.

Can we reach herd immunity by letting everyone get infected?

For diseases where we have safe and effective vaccines, it is much better to reach herd immunity by getting everyone vaccinated than it is by waiting to have everyone get infected. We know the severe, terrible consequences of COVID-19, and so we’re looking for a safe vaccine that can prevent the infection.

Once a vaccine is available to the general public, how do we continue to make sure it is safe?

In the United States, we have incredible systems to track vaccine safety. One system allows everybody to report if they’ve had an adverse event—a bad side effect—after they get a vaccine. That’s not just doctors and nurses; it’s anybody in the public who may have received the vaccine. A group of scientists, working through the U.S. Centers for Disease Control and Prevention (CDC), investigate all of those cases to see if there’s a potential problem. Other systems look at big databases and compare people who have gotten the vaccine to people who didn’t get the vaccine, and look for potential side effects or adverse events, really rare things. They compare the rate in the group who get the vaccine to the group who did not get the vaccine to see if there is a cause between the vaccine and that rare side effect. With all these systems in place, I’m comfortable giving vaccines to my patients, and to my children, because I know that these systems work.

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