Vaccines are less effective in obese adults than in adults with a lower body mass index (BMI), according to research, a disparity that will likely affect vaccines against the novel coronavirus, as well—meaning America's obesity epidemic could hinder the country's effort to control its coronavirus epidemic, Sarah Varney writes for Kaiser Health News.

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Obesity, the immune system, and vaccines

In the United States, more than 107 million adults have BMIs that classify them as obese—a condition that, according to CDC, places them at a higher risk of developing severe cases of Covid-19, the disease caused by the new coronavirus, and at increased risk of dying from the disease.

According to Varney, some scientists in the field of immunometabolism believe those heightened risks stem from obesity's effects on a person's immune response. She explains that, while a healthy immune system triggers on and off inflammation as needed, the immune systems in individuals who are obese tend to maintain a constant state of mild inflammation.

And that difference can affect the way some vaccines work, Varney writes. According to Varney, vaccines are designed to leverage the immune system's inflammatory response to protect against a pathogen, but chronic inflammation in obese adults appears to interfere with that process and weakens the vaccinations.

Chad Petit, an influenza virologist at the University of Alabama, told Varney that obesity might cause a metabolic dysregulation of T cells, which play a critical role in the body's immune response.

According to Varney, scientists first discovered that obesity can affect a person's response to a vaccine in 1985, when researchers found that, during a period of 11 months after vaccination, immunity to hepatitis B declined more quickly among hospital workers who were considered obese when compared with workers who weren't considered obese.

Since then, other research has found similar occurrences among individuals who were considered obese regarding vaccinations against hepatitis A, influenza, rabies, and tetanus.

For example, researchers at the University of North Carolina-Chapel Hill in a study published in the International Journal of Obesity in 2017 found that adults who were considered obese and had received flu vaccinations were two times more likely to contract the flu or develop a flu-like illness than vaccinated adults with lower BMIs. The researchers also found that vaccinated adults who were considered obese had developed antibodies to the flu, but they still experienced worse flu-related outcomes than vaccinated adults with lower BMIs.

In 2015, researchers from Mayo Clinic's Vaccine Research Group in a study published in the journal Vaccine wrote, "Obesity is a serious global problem, and the suboptimal vaccine-induced immune responses observed in the obese population cannot be ignored."

Will a vaccine against the new coronavirus be less effective in adults with obesity?

Now, obesity researchers are raising alarms about the possibility of a vaccine against the new coronavirus being less effective in adults who are considered obese, Varney writes.

"Will we have a [coronavirus] vaccine next year tailored to the obese? No way," Raz Shaikh, an associate professor of nutrition at the University of North Carolina-Chapel Hill, said. Further, Shaikh added, "Will [a coronavirus vaccine that does become available] still work in the obese? Our prediction is no."

But some researchers are hopeful.

For instance, Petit told Varney that he believes researchers can develop an effective coronavirus vaccine for adults with obesity.

"It's not insurmountable," he said. "We can design better vaccines."

Varney notes that researchers are including adults with high BMIs in clinical trials on coronavirus vaccine candidates—something that hasn't always been done in the past.

And Timothy Garvey, an endocrinologist and director of diabetes research at the University of Alabama, stressed that just because vaccines may be less effective in people with obesity, it doesn't mean the inoculations aren't effective at all.

"The influenza vaccine still works in patients with obesity, but just not as well," Garvey said, adding, "We still want them to get vaccinated" (Varney, Kaiser Health News, 8/6).