"We know from other vaccines that have been tested in obese populations that these individuals don't respond as well to these vaccines," said Dr. Matthew B. Laurens, a lead investigator at the University of Maryland for one of the country's most advanced coronavirus vaccine trials by Moderna Therapeutics in a report by ABC News.
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In 2017, researchers at the University of North Carolina at Chapel Hill found that obese adults were twice as likely to be infected with the flu or flu-like illnesses compared to non-obese adults. The study suggested that while medical experts are still trying to fully understand the phenomenon, there are some theories behind the disparities.
"The differences that are seen in the vaccine response in obese people were really noticed as early as 1985," said medical director of diagnostic biology at Houston Methodist Hospital Dr. Wesley Long.
"There's a variety of theories. Everything from the fact that maybe the needles that we use to give vaccines are too short to effectively get into the muscle to deliver the vaccine in obese people to perhaps, because of a larger body mass, maybe a larger dose of vaccine needs to be used and, also, that perhaps it's a sort of chronic inflammatory state that's present in people who are obese and may interfere with the immune response to vaccines."
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Historically, many clinical trials for vaccines have excluded obese people due to chronic medical conditions that could alter trial results. However, Long said that's beginning to change.
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"We don't have any data, as far as I know, about COVID-19 vaccines, but this is one of the reasons why you have to do those large phase three clinical trials," said Dr. Peter Hotez, the dean of the National School of Tropical Medicine at Baylor College of Medicine. "You can't rush them, because you want to be able to look at different populations, and there are different vaccines rolling out through Operation Warp Speed. So some vaccines may work better in some populations than others."
Doctors say it is still critical for everyone to get vaccinated to minimize any risks for complications caused by infection.
"It's really our best hope at controlling this pandemic and even if obese people have perhaps less of a protective response," Long said. "One thing we know with the flu vaccine is that it's very good, and with influenza, it's very good at preventing hospitalizations. So even if you are obese, you are much better off having had the flu shot and having some response than not having the flu shot because, again obese individuals are at higher risk for complications from influenza and from COVID-19. They tend to have other comorbidities that make them at higher risk of infections, so having some amount of protective response from vaccinations is going to be more beneficial than having no response at all."
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