Should people get a Pfizer 'booster' shot after receiving Johnson & Johnson? Experts weigh in.

As experts warn that some regions of the U.S. may be susceptible to "dense outbreaks" of the coronavirus Delta variant, some doctors are suggesting that individuals who received the Johnson & Johnson vaccine consider getting a shot of Pfizer or Moderna as a "booster." The advice coincides with research showing that Moderna's and Pfizer's vaccines, which rely on messenger RNA, may provide "lasting immunity."

But who is a candidate for this additional shot, and what are officials saying? Here's what you need to know.

Experts aren't necessarily opposed to the idea — and some are doing it themselves

Dr. Gregory Poland, co-director of the Mayo Clinic's Vaccine Research Group, says the idea of mixing vaccines isn't unprecedented. "The first time kids below the age of 8 get the flu vaccine, they're supposed to get two doses," Poland tells Yahoo Life. "You know, we try to give the same thing, but it's not always possible just because of supply." (There are multiple types of flu vaccines.)

It's one of several reasons that Poland says he's not necessarily opposed to mixing the COVID-19 vaccines. "Do I think it's an unsafe thing to do? No, I don't have any reason immunologically to think that it would be unsafe," Poland says. "Do I think it's likely to lead to higher antibody levels? Yes, definitely."

Dr. Angela Rasmussen, a virologist at the University of Saskatchewan's Vaccine and Infectious Disease Organization, shared a Twitter thread about her decision to get the Pfizer shot as a booster. "We know that the single-dose J&J regimen is highly protective against severe disease but not as protective against symptomatic disease as mRNA, meaning it’s less protective against infection," Rasmussen tweeted.

Formerly at Columbia University in New York City, Rasmussen received the Johnson & Johnson vaccine in April but decided to get the Pfizer shot in Canada, where she now resides. One of the motivations behind the decision was the availability of mRNA vaccines, another was the increasing spread of the Delta variant. "I think I did the right thing to make sure I am as protected as possible from the Delta variant and thus am protecting others who only have one shot," Rasmussen wrote.

Infectious disease organizations have yet to comment, but a study from the U.K. is promising

U.S. officials have yet to release any statements about the mRNA COVID-19 vaccines being used as a booster, and Poland says they're not alone. "There is no official recommendation, anywhere, for anybody to do that," says Poland. "No official body is recommending that. [But] what the studies show is that you do get better immunity compared to just one dose of adenovirus vector vaccine."

The study Poland is referring to is one from researchers at the University of Oxford, released earlier this week, which gave a major boost to the idea of mixing COVID-19 vaccines. The study found that those who were given a dose of the AstraZeneca vaccine followed by a Pfizer shot achieved the same level of immunity as those given two shots of the Pfizer vaccine. The AstraZeneca vaccine, while given in two doses, is the same type of vaccine as Johnson & Johnson's, relying on a modified virus (or an "adenovirus vector") instead of mRNA to deliver the genetic code needed to fight SARS-CoV-2.

The vaccines may work in different ways, but they're all heading for the same target

Poland says it's too soon to say for sure if adding an mRNA vaccine to the J&J vaccine bolsters immunity, but if it works there's likely a simple explanation: They're both training the body to recognize SARS-CoV-2's distinctive spike protein. Poland has a unique way of explaining it. "So I [recently] rented an Infiniti to get to the airport, but we own a Honda Accord," he says. "I can get to the airport in much more style and faster ... in that Infiniti than I can in my Accord. But they are both on the same highway leading to the same destination. By analogy, it's the same with these two different vaccines."

Dr. Monica Gandhi, professor of medicine and associate division chief of the division of HIV, infectious diseases, and global medicine at the University of California, San Francisco, also tweeted a helpful thread about the two. "Remember that J&J and mRNA vaccines are actually not that different — J&J has DNA inside an adenovirus 'vector' (that brings it in), and mRNA vaccines have mRNA inside a lipid envelope," she wrote. "That mRNA is then 'translated' into a part of the spike protein by your machinery and you see that spike protein, think it's different, and raise a vigorous immune response against it."

Those interested should talk to their doctor and consider their own risk factors

While a number of leading experts seem to be endorsing the idea of getting a booster shot, Poland says it's important to talk to a health care provider and weigh the risks versus benefits. "Would I worry about this if the patient was a young, healthy kid? No, not at all. The risk is low to begin with. A single dose of vaccine clearly protects them," says Poland. "What about if you're a 70-year-old smoker who's obese and got the J&J vaccine? I'd consider it. So what I'm saying is to think of it as a gradient. One might consider doing it, even in the absence of a robust database, when your risk of doing nothing is perceived to be higher than the risk of doing something."

The Centers for Disease Control and Prevention has declared the Johnson & Johnson, Moderna and Pfizer vaccines "safe and effective" with the most common side effects — fever, body aches and muscle pain — disappearing within a few days. The organization is currently looking into rare occurrences of myocarditis, an inflammation of the heart muscle, following the Pfizer and Moderna vaccines.

Both Rasmussen and Gandhi seem to agree. "Sometimes public health requires making tough decisions without a complete data set to support it," Rasmussen tweeted. "Humility in COVID means we change our recommendations with changing data," added Gandhi. For more information about the COVID-19 vaccines, potential side effects and vaccination centers, visit the CDC.

Read more from Yahoo Life:

• How to reduce anxiety about going maskless in public, according to experts

• Sweet 16 vaccine: Teens hope getting vaccinated will 'give us our lives back'

• Here's how experts recommend staying safe and cool in extreme heat

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