Scientists suspect that a potential COVID-19 vaccine would be less effective in protecting obese Americans from the disease, which has infected millions worldwide and killed more than 157,000 in the U.S. alone.

In a  new report from CNN and Kaiser Health News, researchers pointed out that other prominent vaccines dating back to 1985 -- like those for the flu and hepatitis A and hepatitis B -- have not worked as well in providing immunity for obese adults.

“Will we have a COVID vaccine next year tailored to the obese? No way,” Raz Shaikh, an associate professor with the University of North Carolina’s nutrition department, told Kaiser on Wednesday.

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That said, those with obesity are still highly encouraged to obtain vaccinations.

A doctor takes blood samples for use in a coronavirus vaccine trial in Oxford, England in June 2020.  (John Cairns, University of Oxford via AP)

“The influenza vaccine still works in patients with obesity, but just not as well,” the University of Alabama’s Director of Diabetes Research Dr. Timothy Garvey explained.

In the United States, over 40% of American adults are considered obese, and the Centers for Disease Control and Prevention has cautioned they face an increased risk if they contract COVID-19.

While obesity has long been recognized as a significant risk factor for death from things like cardiovascular disease and cancer, immunologists have found it also negatively impacts the body's immune response, Kaiser reported.

"Obesity is a serious global problem, and the suboptimal vaccine-induced immune responses observed in the obese population cannot be ignored," a Mayo Clinic Vaccine Research Group noted in a 2015 study published in the journal Vaccine and cited by Kaiser.

While people with high Body Mass Index (BMI) measurements have historically been excluded from drug trials -- reportedly because of chronic conditions that would interfere with the results -- today's clinical trials for a COVID-19 vaccine do not have a BMI exclusion, according to Dr. Larry Corey, who oversees the phase III trials sponsored by the National Institutes of Health.

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As scientists like Corey search for a vaccine to combat the infectious disease, experts like White House coronavirus task force coordinator Dr. Deborah Birx have warned the nation is now in a “new phase” of the pandemic.

According to data from the Johns Hopkins Coronavirus Resource Center, there have been over 4.7 million confirmed cases in the U.S. and more than 18 million worldwide.