Should You Get A Pfizer Or Moderna COVID-19 Booster If You Had The Johnson & Johnson Shot?

Here's what experts think about mixing vaccines and if there's a need for an extra dose with the delta coronavirus variant.
Will mixing vaccines boost your protection against the delta coronavirus variant?
Marko Geber via Getty Images
Will mixing vaccines boost your protection against the delta coronavirus variant?

With the delta variant quickly gaining traction across the United States, many people who originally got the Johnson & Johnson vaccine are now wondering if they need a dose of either the Pfizer or Moderna shot to boost their protection against COVID-19.

A preliminary report from the United Kingdom looked into the need for booster shots and found that mixing doses of different coronavirus vaccines could enhance antibody production and may — in theory — keep you safer, at least in the short term.

But that’s just one study that is still in the works, and many infectious disease experts don’t think booster shots will be necessary right now since all of our shots appear to be effective against the variants we’ve seen so far. Even if some think boosters are a good idea, we need much more research to determine if, when and how booster shots should be administered.

Here’s what to know about booster shots and the delta coronavirus variant if you got the J&J jab.

You can probably hold off on boosters for now

Monica Gandhi, an infectious disease specialist with the University of California, San Francisco, said there is currently no data suggesting we need to boost the Johnson & Johnson vaccine. There also isn’t any strong evidence that we are seeing more breakthrough infections in people who got the J&J shot versus an mRNA vaccine like Pfizer or Moderna.

“That, to me, is as proof positive that you do not need an mRNA vaccine after,” Gandhi said.

Antibody levels always wane after infection or vaccination — that’s to be expected. If scientists were only measuring antibodies, we would be boosting constantly, Gandhi said.

But our immune system is robust, and in addition to antibodies, we have our cell-mediated immune response, which includes T-cells and memory B cells. These virus fighters hang out in our lymph nodes and germinal centers and are activated upon exposure to a pathogen. While our antibodies only recognize the spike protein on the coronavirus, T-cells recognize many different parts of the coronavirus ― so even if the virus mutates, we’ll still be well-protected against severe disease. And when the memory B cells turn on, they create new antibodies. That means when detectable antibody levels wane, research shows, we’ll still be able to produce new antibodies targeting the new virus or variant.

When researchers talk about immunity, they often refer to antibodies because those are the easiest to measure. A recent study from the U.K. found that when the AstraZeneca and Pfizer shots were combined, people produced a stronger antibody response in the first few weeks. This adds up, since evidence shows immunity from the the AstraZeneca and J&J shots gradually ramps up several weeks following vaccination; but it doesn’t necessarily mean that combining the two was needed. The study also concluded that the best course of action is to get two doses of the same vaccine, since clinical trials already have shown that method works.

T-cells and B cells are trickier to measure, and doing so requires a lot of time and expensive technology. “Just because the antibodies are higher after two doses of a mix-and-match strategy does not actually reflect your T-cells or memory B cells,” Gandhi said. Previous studies have found so far that our T-cells work against the alpha, beta and gamma variants of the virus.

There probably isn’t any harm in taking an extra dose, but there also doesn’t seem to be a need as of now. Plenty of people who experienced anaphylaxis after one of the mRNA shots followed up with a J&J shot and were just fine, according to Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins University Center for Health Security.

The J&J and mRNA shots aren’t so different that two are necessary

If you look at the technologies behind the J&J, AstraZeneca and mRNA shots, you’ll see that the vaccines aren’t all that different. According to Gandhi, Pfizer and Moderna use mRNA to teach our bodies how to identify the coronavirus and prevent infection; the J&J and AstraZeneca shots use DNA that tells our body to produce mRNA and then go through that same process. They all ultimately go after the spike protein and make the same antibodies and T-cells.

The Johnson & Johnson, AstraZeneca, Pfizer and Moderna shots are effective against all variants at preventing hospitalization, severe disease and death. That is, after all, the goal of the shots.

“J&J will likely be able to do that with flying colors against the delta variant,” Adalja said. The big thing worth tracking is whether any breakthrough infections post-vaccination are causing serious illness or if they are mostly mild or asymptomatic cases (the latter appears to be the case and indicates the shots are still working great). If breakthrough infections start becoming more serious, a need for boosters could become more likely.

Scientists will keep looking into the need for boosters

All that said, booster shots are still worth looking into to understand how our vaccines can be improved and fine-tuned going forward. Adalja is more interested in seeing how vaccines with very different technologies — like a Pfizer dose followed by something like the Novavax shot, which uses lab-grown copies of the virus’s spike protein — could impact protection.

There is one group who could wind up benefiting from boosters: people who are immunocompromised. Early data suggests that those with weakened immune systems might not produce as strong an immune response after vaccination.

“It’s a promising thing to study, especially for populations like the immunosuppressed where they may have a blunted response to one type of vaccine, and when you combine it with another they get a more robust response,” Adalja said.

But, for now, there just isn’t enough evidence to say whether people who got the J&J shot are more at risk for catching COVID-19 compared to those who got one of the mRNAs. Hopefully, we’ll have more data on that soon.

The best course of action in the interim? “Continue to enjoy your immunity from the J&J vaccine,” Adalja said.

Experts are still learning about COVID-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.

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