MARY LOUISE KELLY, HOST:
As the COVID-19 vaccine rolls out, three big questions remain. First, can someone who has been vaccinated still spread the disease? Second, will the vaccine remain effective as the virus itself evolves? And third, how long will the vaccine last? NPR's Richard Harris says immunologists are hard at work getting the answers.
RICHARD HARRIS, BYLINE: Let's start with the first question about whether people who are vaccinated can still spread the disease. Marion Pepper, an immunologist at the University of Washington, says that's not just an open question for this vaccine, but for vaccines in general.
MARION PEPPER: It's hard to say because we're constantly being bombarded by different pathogens, and we don't know when our immune system is responding.
HARRIS: We may have infections that don't make us sick, so we never know about them, but we could be spreading disease. Michel Nussenzwei, a Howard Hughes investigator at the Rockefeller University, says it's possible that your immune system won't completely prevent the virus from starting to multiply inside you after an infection.
MICHEL NUSSENZWEI: Spreading it is really a function of how much virus you're producing.
HARRIS: If your immune system ramps up quickly enough, that could prevent a virus from starting to multiply.
NUSSENZWEI: It's a bit of a race between the immune system and the virus.
HARRIS: It seems likely the vaccine will prevent you from spreading significant amounts of virus, but scientists are still trying to nail that down. The second question about whether the vaccine will remain effective even as the virus evolves is harder to answer. Scientists aren't concerned about the current mutations. And longer term, Pepper says your immune system does have ways to adapt.
PEPPER: Even though everyone is obviously concerned about a virus evolving, your memory B cell responsiveness also evolves over time.
HARRIS: Memory B cells remember an infection and help your immune system produce antibodies. And they don't just remember viruses they've encountered. Remarkably, they can generate antibodies that have random changes in them, and those can help defend against a new strain of virus.
PEPPER: It's pretty much the only time in the body where a mature cell introduces mutations intentionally into the DNA.
HARRIS: Clearly, there are viruses that can evade this clever system, which is why you need a new flu shot every year. For COVID, we'll have to wait and see. Finally is the question of how long a vaccine will last. Stephen Jameson at the University of Minnesota Medical School says, in some instances, your immune system can have a very long memory.
STEPHEN JAMESON: Some kind of natural infections, it can give you lifelong immunity. You only get it once. You're protected for the rest of your life.
HARRIS: Vaccines mimic a natural infection to trigger an immune response, but they may require a boost to keep that immunity strong. That depends on the nature of the infection. In the case of people with COVID-19, there's already evidence that immunity will last for many months, but beyond that is an open question.
JAMESON: The good thing is that there would be the opportunity that if turned out there was some waning of immune response, then like many other vaccines, maybe there would have to be another booster. Maybe you get another booster after a year or something.
HARRIS: These questions reflect how much scientists have come to understand about our immune system in recent years. Marion Pepper says COVID is also illuminating what we still don't know about how the immune system defends us from viruses.
PEPPER: It's been really interesting to watch this unfold in real time 'cause we're learning so much about this virus and the immune response to it in a way that we've never done previously.
HARRIS: I asked Michel Nussenzwei another big-picture question.
Are we going to be saved by our immune system?
NUSSENZWEI: Yes, we are for sure.
HARRIS: Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.
