What Should I Know About COVID-19 Vaccine Boosters?

Dr. Paul Offit explains why a third dose of COVID-19 vaccine is being considered and what to expect.


What should I know about COVID-19 vaccine boosters?

Paul Offit, MD: Hi, my name is Paul Offit. I'm talking to you today, September 1st, 2021, from the Vaccine Education Center at the Children's Hospital of Philadelphia. One thing that has recently dominated the news is whether or not we need a third dose, or a booster dose, for mRNA vaccines. The Biden administration had several weeks ago made that statement that everyone in the general public who has received two doses of mRNA vaccines could reasonably then receive a third dose eight months after the second dose.

So, where does that recommendation come from? The thinking is that if we're to have a vaccine that is effective, the goal of the vaccine is to prevent serious or critical illness; the kind of illness that causes you to be hospitalized or go to the intensive care unit or die. So, have these two mRNA vaccines held up well in protection against serious disease? The answer is to date, yes, very well. Both vaccines have held up well in protection against serious disease, and that you have greater than 90% protection, including against the delta variant, for both vaccines. So, if that's true, then why a third dose?

Well, one thing that's happened is there has been an erosion in the level of neutralizing antibodies over time induced by these two vaccines. Associated with that, there's also been an erosion in protection against asymptomatic infection or mildly symptomatic infection or even low-moderately symptomatic infection, where you still could be contagious and infect others. So, is it then a value to give a third door to try and increase the neutralizing antibodies and then decrease the contagiousness, if you will, of those who now are fairly long after that second dose? And I think there is some value in that, but it does seem to go against what is our central concern, which is protecting against serious illness. The difference is, is that usually protection against serious illness is mediated by so-called memory cells. These are long-lived cells — memory B cells are the kind of cells that make antibodies that protect you, or memory T helper cells, which are the kind of cells that help B cells make antibodies, or memory cytotoxic T cells, which are the kind of cells that kill virus-infected cells. There are a number of studies that have shown those are long lived. So, the anticipation is then that protection against serious illness will probably last for a fairly long time, a year or two years or three years, maybe even longer. So, we'll see. But for now, I think that the goalpost has moved a little bit where we're saying that we want to protect against not only severe disease, but even mild or asymptomatic infection, hence the notion of a booster dose.
I think we're going to learn a lot more about this by the end of the month. The Food and Drug Administration's Vaccine Advisory Committee will be meeting on this in the month of September. The Centers for Disease Control and Prevention will then also meet, and my recommendation would be to sort of hold on until the end of the month until we see what exactly is going to be the recommendation for this so-called booster dose or three-dose product, and we’ll see.

Thank you very much for your attention.

Related Centers and Programs: Vaccine Education Center

Last Reviewed on Sep 03, 2021