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.

Kristin Oliver, MD, MHS

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.

There are new headlines every day about the rapid development of vaccines to prevent COVID-19.In this Q&A, Gopi Patel, MD, Hospital Epidemiologist at The Mount Sinai Hospital, Medical Director for Antimicrobial Stewardship for the Mount Sinai Health System, and Associate Professor of Medicine (Infectious Diseases) at the Icahn School of Medicine at Mount Sinai, addresses some of the most pressing COVID-19 vaccine questions.

In general, how do vaccines work?

Vaccines expose us to pieces of either a bacterium or a virus, and our body mounts an immune response by making antibodies against those pieces. Antibodies are proteins that fight germs like viruses and bacteria by latching onto and disabling them. The goal is that our body will then recognize those pieces and use the antibodies to fight off any future exposure to the real bacteria or virus.

Can a COVID-19 vaccine give me COVID-19?

No.  None of the vaccines in advanced clinical trials can give you COVID-19.

Gopi Patel, MD

Should I get a COVID-19 vaccine if I already have antibodies?

We are learning a lot more about the human response to COVID-19. A lot of people who have had COVID-19 did mount an antibody response, but we don’t know yet how long that response might last. So right now, if you have a history of COVID-19 it is still worthwhile to get a COVID-19 vaccine when they become available.

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

The Food and Drug Administration (FDA), pharmaceutical companies, and scientists who are involved in vaccine development are all very committed to developing a safe and effective vaccine. There is rigorous testing for all vaccines to ensure safety. During any vaccine clinical trial, side effects or adverse events—health problems that happen after the vaccine is given, which may or may not have been caused by the vaccine—are recorded and monitored by safety monitoring boards before the vaccine becomes publicly available through either an Emergency Use Authorization or through FDA approval. All that data is made available and will be quite transparent. The goal is a safe and effective COVID-19 vaccine.

What if many people do not get a COVID-19 vaccine?

It is hard to say. Currently, the recommendation from the FDA is that if a COVID-19 vaccine is made available, it has to be at least 50 percent effective. That means when you test the vaccine in clinical trials, the group of people who got the vaccine has at least 50 percent fewer cases of COVID-19 than the “placebo” group who didn’t get the vaccine. I think there are lots of questions about how many individuals need to be vaccinated to reach what we call herd immunity, where the rate of immunity throughout a community makes the spread of a particular disease between individuals less likely.

What is herd immunity?

Herd immunity is the idea that you can protect vulnerable people if most of the population gets vaccinated and develops an immune response. We talked about this with something that hit New York hard in 2019, which was the measles. In the case of measles, when most people are vaccinated, that protects those individuals who cannot get vaccinated—the very young or those who have immune systems that can’t respond to the vaccine. So that’s the idea of herd immunity. It is very unclear at this point what herd immunity means for COVID-19. It may be that a lot of people may make antibodies, but we also have to make sure people don’t transmit infection. So practices like wearing masks, washing hands, and watching your distance are still really important, even in the setting of a vaccine.

How is Mount Sinai involved in the testing of a COVID-19 vaccine?

We’re very lucky at the Mount Sinai Health System in that we are actually involved in trials of COVID-19 vaccines. We’ve been involved in the trial of the Pfizer vaccine, one of the candidates that is furthest along in the process, and we’re starting enrollment in other trials soon. So we are prepared in terms of looking at the safety and efficacy of the four vaccines that are most advanced in Phase 3 clinical trials.

How is Mount Sinai planning for administering a vaccine once it becomes available?

Mount Sinai is already looking at how we would distribute and allocate a vaccine. It is important to remember that this vaccine would be administered under an Emergency Use Authorization from the FDA. So what would that look like? Who would we offer vaccination to, and how would we monitor those individuals? How would we make sure that we offer the vaccine to those who are most vulnerable to COVID-19 infection, whether it be in the community or in the health care setting? We know our health care workers are at risk. But we also know there are essential workers outside of health care who may be at risk. We’re working with our public health authorities—including the New York State Department of Health and our New York City Department of Health and Mental Hygiene—and watching the safety and efficacy data closely. Members of our Icahn School of Medicine at Mount Sinai faculty are working with New York State on the safety, efficacy, and evaluation of any vaccine candidate that becomes available in the next few months.