RALEIGH – The National Institutes of Health announced August 18 that it is recommending booster shots for people who were vaccinated with mRNA vaccines (Pfizer and Moderna) against COVID-19. People should consider getting their vaccine boosters eight months after they received their second dose of Pfizer or Moderna. But what are booster shots? And why are they needed?

To address those questions, we spoke with Matt Koci, a virologist and immunologist whose work focuses on host-microbe interactions in birds. Koci is a professor in NC State’s Prestage Department of Poultry Science.

This post is part of a series of Q&As in which NC State experts address questions about the vaccines on issues ranging from safety to manufacturing to distribution.

The Abstract: What is a booster?

Matt Koci: Great question. In the past I’ve described vaccines as vocational training for your immune system, as compared to on-the-job training from getting an infection. To extend that analogy a bit further, booster shots are like refresher courses. You took the class and passed, but you haven’t had to use that skill on the job yet. Now that it’s been some time since you graduated, you haven’t forgotten the material completely, but you know if you were to retake the exam you wouldn’t do as well as you did before. Then your boss tells you, “I know we hired you because you took those courses and we haven’t given you the chance to show what you can do. Don’t worry, in the next few weeks I’m sure you’ll get the chance to shine.” You’d likely go home and start reviewing your old notes.

That’s the job of a booster shot. You got the vaccine. It taught your immune system how to respond to the disease so it would be ready to handle it as soon as it showed up. However, with masks and social distancing, your immune system hasn’t needed to flex those new skills. Now that cases are as high as they’ve been at any point during the pandemic, and people aren’t hunkered down in their homes like they were, the chances that you need your immune system to be at the top of its game are as high as ever. So, booster shots help make sure you’re ready.

One thing to point out: the booster shots the CDC has recommended people start getting is just another dose of the vaccine, against the same version of COVID. It is not specific to the delta variant. Delta is different enough from the original virus that the vaccine doesn’t work as well as it did against the original COVID virus. However, the vaccines still work well enough that there isn’t a need for a new, variant-specific vaccine – at least not yet. I wanted to mention that, because I know some people, and some physicians, have been confused when trying to find a place to get their booster, thinking it was a different vaccine or was being given at different locations. Any place giving out vaccine will do.

TA: Why are boosters being recommended for people who received the Moderna and Pfizer vaccines?

Koci: The short answer is, around the world we’ve seen the levels of antibodies start to drop after about six months after your second shot. This decrease in antibodies isn’t a lot. Antibody levels are actually high enough to fully protect you from the original version of COVID. It’s not that the vaccine isn’t as good as you were told, it’s that we’re fighting a different variant of the virus now.

The delta variant is just different enough from the original COVID virus that the drop off in antibody level after six months seems to make a difference in how many people are getting mild-to-moderate infections with the delta variant. The idea behind getting the booster now is that it will help get the immune system back up to its peak performance, which will hopefully help reduce the number of breakthrough infections, and/or ensure those infections are as mild as possible.

I should also point out that boosters are especially important for those who have immunocompromised conditions, and therefore may not have gotten the full benefits from the first two shots in the first place. The third shot should help ensure these people get as much protection as possible since so far the herd has let them down.

TA: What about Johnson & Johnson?

Koci: I honestly do not understand why they didn’t give guidance for those who got the J&J shot. Reports in the media have made it sound like the J&J vaccine isn’t as good as the mRNA vaccines, but I don’t think we have the data to make that conclusion. I believe the J&J vaccine is on par with the mRNA vaccines for protecting you from severe disease and death, but the media reports have scared a lot of people who got the J&J shot. It’s extremely frustrating that the CDC has not yet addressed questions about boosters for the J&J vaccine. I expect recommendations for booster shots for those who got the J&J vaccine will be coming soon.

TA: Are you going to get a booster shot?

Koci: Absolutely.