I topped off my Johnson & Johnson vaccine with a Pfizer chaser. Here's why

When I got the Johnson & Johnson vaccine in March, I was elated. I could finally go back into the world with a decent amount of confidence and protection — or so I thought. The Delta variant soon became dominant and cases soared in some regions so two weeks ago, I decided to get a shot of the Pfizer vaccine. As you’ve probably heard, mixing and matching vaccines is controversial, and the C.D.C. does not recommend that people follow their J&J shot with a Pfizer chaser. So, why would I treat my body like a petri dish by mixing vaccines?

My decision was partly emotional; I simply craved more protection. As a health journalist, I spend a lot of my day parsing through COVID-19 research and articles. And while professionally, I work hard to make sure that my reporting on the pandemic is accurate and candid without being panic-inducing, personally, I am a paranoid person.

I bought N95 masks as soon as I could get my hands on them and I never stopped masking in public — even when the C.D.C. said it was okay. When Delta first started spreading in my hometown of New Orleans, I feared that infection rates would rise quickly (they have, by the way) and I did not want to be part of the problem. I wanted to feel like I was keeping myself and my community as safe as humanly possible.

But part of my decision to top up my vaccine was based on information and logic. Some experts were skeptical from the beginning that any one shot vaccine would be effective. Most assured us that it was, but then the Johnson & Johnson rollout spawned an unexpected controversy — a few people had scary side effects after getting the Johnson & Johnson vax — and some states paused administering it.

New research confirms that the Johnson & Johnson vaccine may not be that effective against Delta and other emerging variants, which worried me. So I made a decision and stuck to it. But for you, dear readers (and for my own peace of mind, too) I asked experts to help me investigate if taking a second vaccine is actually safe or necessary.

“I understand this anxiety,” says Jason Gallagher, an infectious disease pharmacist in Philadelphia and clinical professor at Temple University School of Pharmacy. Gallagher felt that way himself, he says. “I received the J&J vaccine in a trial in November, and as the Delta variant began to spread, I became concerned about a lack of data with the J&J vaccine and took a dose of the Pfizer mRNA vaccine in June,” Gallagher says. He had travel planned and wanted to keep himself and others as safe as possible.

Gallagher’s decision was based on science. When the Delta variant appeared, no one could be sure that the current vaccines would be effective against it, he explains. The seemingly contradictory research made him suspicious about whether the antibodies that the J & J vaccine induces would be effective against the Delta variant. “An initial report showed that they were active [in combating Delta], then another one suggested otherwise,” he says. “The conflicting data is really frustrating and not logical.” Since the data on Johnson & Johnson wasn’t conclusive, Gallagher made a decision based on the research done in the U.K. on combining the AstraZeneca vaccine with the Pfizer vaccine, he explains.

For the non-scientists among us: Johnson & Johnson’s one-shot vaccine is a different kind of immunization than the Pfizer and Moderna shots. The J&J and AstraZeneca vaccines are adenovirus vaccines (the "traditional" type). They "use a harmless virus to introduce the instructions on how to fight infection," Gallagher explains. "They use the virus to deliver the instructions."

The Pfizer and Moderna vaccines are mRNA vaccines — which use a newer type of technology — to deliver a copy of the instructions, not relying on a virus to deliver them, he adds. "Viruses normally deliver instructions on how to make new viruses; these vaccines deliver instructions on how to fight them."

Since these two different kinds of vaccines affect the body in different ways, it is possible that taking both could create a stronger defense against COVID. Also, some research suggests that the new mRNA vaccines may have some unexpected benefits that we are just learning about.

Studies done at Oxford University suggest that combining adenovirus and mRNA vaccines produces a more robust immune response, and data from a study in South Korea suggests that following a shot with AstraZeneca with Pfizer may induce up to six times as many neutralizing antibodies than two doses of AstraZeneca.

The clinical studies about combining J&J with another vaccine are just launching now, so we don’t actually know whether double vaxxing with the vaccines available in the U.S. is safe or effective. But even with what we know, the logic behind chasing my J&J shot with a Pfizer shot is not far-fetched at all. For all intents and purposed, it could serve as a booster.

Angela Rasmussen, a virologist at Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada, tweeted about getting a shot of the Pfizer vax in June after having taken the Johnson and Johnson dose in April. And Vin Gupta, a pulmonary critical care physician in Seattle, announced on Twitter at the end of June that he had done the same. “Most I know who got J&J are doing it and are telling others the same — since two seem better than 1 re: delta,” he tweeted.

The logic behind chasing my J&J shot with a Pfizer shot is not far-fetched at all. For all intents and purposed, it could serve as a booster.

Other experts I spoke with agreed that combining adenovirus and mRNA vaccines does show promise. “With emerging variants, there may be some benefit to ‘boosting’ the adenovirus vaccines with another shot,” says Bruce Patterson, a virologist in Palo Alto who studies long haul COVID-19. “Benefits may include a stronger and more robust immune response,” he says. There aren’t any obvious risks to combining, it may just be overkill, especially since adenovirus vaccines become more effective over time, Patterson explains.

In other words, we haven’t actually studied the J&J vaccine long enough to know how effective it can become on its own, so people who got this jab may not actually need another vaccine.

The reality is that there’s a lot we don’t know — like the potential risks or side effects of mixing different types of vaccines. But we do know that all of the current vaccines are pretty damn effective. And experts want us to know that our anxiety about needing more protection against emerging variants is totally natural and warranted. “People who are vaccinated may still have a breakthrough infection, but it is likely to be no worse than a cold if it even happens,” says Gallagher. “They are in a much better place than the unvaccinated population that is driving the uptick in U.S. cases.” And, as Patterson points out, there could be risks that we don’t know about. “Mixing and matching could also contribute to overstimulating and dysregulating the immune system,” he says.

With Delta raging, it’s pretty clear that there’s a lot we don’t know about the virus or the vaccines. The best thing you can do right now is get fully vaccinated and mask up in places where infection is likely to spread. The jury is still out about whether people who got the J & J jab should double up or if doing so could cause unexpected complications. “I did fine and I don’t regret the decision,” says Gallagher.

Correction 8/9/21: A previous version of this story incorrectly referred to adenovirus vaccines as containing "inactive viruses." It was changed to reflect that these vaccines, instead, contain a harmless version of the virus to introduce immunity to the body.