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KANSAS CITY, Kan. — Pfizer’s request to seek U.S. authorization for a third dose of its COVID-19 vaccine raised questions about the vaccine’s protecting against coronaviruses.

The Centers for Disease Control and the Federal Drug Administration reiterated Friday that people who are fully vaccinated do not need a booster shot at this time. That does not mean that vaccinated people will not need a booster shot in the future.

The CDC, FDA and the National Institutes of Health said they are studying Pfizer, Moderna, and J&J’s vaccines to determine how long the vaccines protect against COVID-19 and its variants. Right now they do not have that answer.

“I think the experts are fully recognizing that a booster dose is going to most likely be required,” Dr. Mark Rupp, infectious Diseases and Infection Control and Epidemiology at Nebraska Medicine, said during a Facebook Live with the University of Kansas Health System Friday morning. “I’ve been very impressed with the data to date to suggest the longevity of the vaccine response and so the longer we go, the better it looks.”

Scientists didn’t start Phase 1 trials of experimental vaccines for COVID-19 until March of 2020. It wasn’t until December 2020 that the UK became the first country in the world to approve a vaccine and begin mass vaccinations. The US began vaccinating people days later.

That means the US has less than a year of data to examine the effectiveness of the vaccine. Health experts said they know the vaccines protect people for at least three months. They expect it to offer full protection for six months, and say we won’t likely need a booster for at least a year.

“The guidance from the CDC and the FDA is still that you are fully vaccinated, more than likely you’re going to still have good protection, both from antibodies, even if some of that protection is reduced over time,” Dr. Dana Hawkinson, Medical Director of Infection Prevention and Control at the University of Kansas Health System, said.

Efficacy isn’t the only question being investigated. Scientists are also trying to determine what happens if you received Moderna’s vaccine, or the single-shot J&J vaccine. Will those versions also need boosters, and will people be able to get Pfizer’s booster, or do they need to stay with the same brand of vaccine?

“Those are clearly some of the questions that still need to be addressed as far as the mixing and matching of the vaccines. There is some information that suggests that actually getting a different form of vaccine may give you a better booster response, a little bit different wrinkle to your immunologic response and they may actually function better than just staying with a synchronous vaccine all the way through,” Rupp said. “We have a lot yet to learn about the booster when it’s going to be.”

There could even be guidance for people who have different diseases or chronic conditions versus those who are considered healthy.

“There may be populations where a booster dose makes a lot of sense and so I already alluded to our immune-compromised patients who may not have responded fully to the vaccine, there’s increasing amounts of information to suggest that a third dose in at least some of those patients will result in a brisk immunologic response and protection,” said Rupp. “So those are the some of the groups that we really need to start looking at where does a booster make sense.”

In the past health experts have suggested that the COVID-19 vaccine could be needed annually, just like a flu vaccine. They say it will likely depend on the number of variants and how many people are eventually vaccinated.