• Researchers say high rates of obesity in the United States could make a COVID-19 vaccine less effective here.
• Experts say obesity, as well as other factors such as diabetes and older age, can inhibit a vaccine’s ability to produce effective antibodies against a virus.
• Experts say when a COVID-19 vaccine is available, everyone — including people with obesity and other conditions — should get the vaccine.

Several promising COVID-19 vaccines have moved into the final stages of clinical trials in order to be approved for use by the general public.

But even when we have a safe vaccine in hand, some experts have raised concerns that the United States’ high obesity rate — as well as other factors — might influence how effective those vaccines are in producing immunity to the novel coronavirus.

“A vaccine is typically utilized to raise neutralizing antibody levels in the body so that an individual can be protected,” said Chris Xu, PhD, chief executive officer of biotech company ThermoGenesis, which has developed rapid COVID-19 antibody tests and studied the disease in detail.

“Researchers believe that due to increased production of leptin (which correlates with body fat mass) and fat, the obese population has a more difficult time gaining vaccine-induced antibody protection,” Xu told Healthline.

More than 40 percent of adults, as well as 18 percent of children in the United States, have obesity, according to the Centers for Disease Control and Prevention (CDC).

That could spell trouble if the eventual COVID-19 vaccines induce a weaker immune response in people with obesity.

Factors that can affect immunity

Scientists first found a link between obesity and lower vaccine effectiveness in the 1970s when studying the hepatitis B vaccine.

Since then, researchers have identified lower vaccine immune response with the influenza A/H1N1 vaccine as well as with rabies and tetanus vaccines among people with obesity.

The reason has less to do with being overweight, per se, as much as the excess inflammation that comes with it, said Dr. John Morton, the division chief of bariatric and minimally invasive surgery at Yale Medicine in Connecticut.

“What we know is that the vaccines in general do not work as well in patients who have obesity,” he told Healthline. “Inflammation can attack the vaccine and make it less effective.”

In fact, people with obesity can often produce healthy levels of antibodies following a vaccine but still display less protection from a virus because of other inflammation-induced deficiencies in the body’s immune response.

That means other inflammatory conditions or conditions that inhibit the immune system — including older age — can also reduce a vaccine’s effectiveness.

“The ability of an individual to be able to respond to a vaccine is dependent on their immune system,” Xu explained. “Data suggests that people that are obese inhibit T-cell activation, which plays an important role in providing protective antibodies.”

Diabetes, which often goes hand-in-hand with obesity, should also get a close look, he added.

“Diabetes has shown to be a risk factor that associates with the weakening of the immune system, therefore, potentially could affect the effectiveness of a vaccine,” Xu said. “In addition, the vaccine’s safety profile in diabetic patients may need to be carefully examined.”

What does this mean for a COVID-19 vaccine?

None of this means that a COVID-19 vaccine will definitely be less effective among people with obesity or diabetes, or those with compromised immune systems.

But it’s something researchers are keeping an eye on.

“It’s possible that we could see a less effective COVID-19 vaccine, similar to how we saw its negative impact on the hepatitis B, influenza A/H1N1, tetanus, and rabies vaccines,” Xu said. “However, COVID-19 is so new, so we don’t have scientific data to prove that yet.”

There’s one silver lining that’s a byproduct of the rapid development of COVID-19 vaccines, however, and that’s that vaccine study participants will include a broad cross-section of the population, including people with obesity.

That matters because drug trials often exempt people with high body mass index scores because health conditions related to obesity can obscure test results, Dr. Larry Corey, the president and director emeritus of the Fred Hutchinson Cancer Research Center in Seattle, Washington, told Kaiser Health News.

It’s possible that future COVID-19 vaccine formulations for obese and other at-risk populations will need to have additional immune response stimulators called adjuvants added to them beyond those in the initial vaccine.

That would be similar to what has recently been done with a special flu vaccine formulation used on adults over age 65.

But for now, it’s still too early to tell.

“These types of questions definitely need answers in assuring the public of the safety and efficacy of newly developed vaccines,” Dr. Larry S. Schlesinger, an infectious disease specialist, chief executive officer, and president of the Texas Biomedical Research Institute in San Antonio, told Healthline.

“Large phase 3 clinical trials will be the first time for us to be able to begin to assess the safety and effectiveness of a given vaccine in a more diverse population, [so] we will gain a lot more insight into the answers to these questions in the next 3 to 6 months,” he said.

The important thing is to get the vaccine once it’s available, no matter what conditions a person is living with, Morton said.

“You should still get the vaccine, because even if it doesn’t work as well, it will still work some,” he said. “It’s one thing that can help.”

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