America’s Covid-19 vaccines could be undermined by the obesity epidemic

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But in the United States, where at least 4.6 million people have been infected and nearly 155,000 have died, the promise of this vaccine is hampered by a vexing epidemic that long preceded Covid-19: obesity.

Scientists know that vaccines designed to protect the public against influenza, hepatitis B, tetanus and rabies may be less effective in obese adults than in the general population, making them more vulnerable to infections and disease. There is little reason to believe, according to obesity researchers, that Covid-19 vaccines will be any different.

“Will we have a Covid vaccine next year suitable for obese people? No way, ”said Raz Shaikh, associate professor of nutrition at the University of North Carolina-Chapel Hill.

More than 107 million American adults are obese, and their ability to return to work safely, care for their families and resume their daily lives could be reduced if the coronavirus vaccine gives them weak immunity.In March, still at the start of the global pandemic, a little-noticed study in China found that heavier Chinese patients with Covid-19 were more likely to die than skinny ones, suggesting a perilous future awaiting the United States. , whose population is among the heaviest. in the world.

And then that future arrived.

As intensive care units in New York, New Jersey, and elsewhere filled with patients, the federal Centers for Disease Control and Prevention warned that obese people with a body mass index of 40 or more – known as name morbidly obese or overweight of about 100 pounds – were among the groups most at risk of becoming seriously ill with Covid-19. About 9% of American adults fall into this category.

As the weeks passed and a clearer picture of those hospitalized emerged, federal health officials broadened their warning to include people with a body mass index of 30 or more. This dramatically expanded the ranks of those considered vulnerable to the most severe cases of infection, to 42.4% of American adults.

Obesity interferes with the immune response

Obesity has long been known to be a major risk factor for death from cardiovascular disease and cancer. But scientists in the emerging field of immunometabolism are finding that obesity also interferes with the body’s immune response, putting obese people at increased risk of infection with pathogens such as the flu and the novel coronavirus.

In the case of influenza, obesity has become a factor making it more difficult to vaccinate adults against the infection. The question is whether this will be true for Covid-19.

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A healthy immune system turns inflammation on and off as needed, calling on white blood cells and sending proteins to fight infection. Vaccines exploit this inflammatory response. But blood tests show that obese people and people with metabolic risk factors such as high blood pressure and high blood sugar experience a state of mild chronic inflammation; the ignition turns on and stays on.

Adipose tissue – or fat – in the belly, liver, and other organs is not inert; it contains specialized cells that send out molecules, like the hormone leptin, that scientists suspect of inducing this state of chronic inflammation. While the exact biological mechanisms are still being investigated, chronic inflammation appears to interfere with the immune response to vaccines, possibly subjecting obese people to preventable diseases even after vaccination.

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Evidence that obese people have a blunt response to common vaccines was first seen in 1985 when obese hospital workers who received the hepatitis B vaccine showed a significant drop in protection 11 months later. , which was not observed in non-obese employees. This finding was replicated in a follow-up study that used longer needles to make sure the vaccine was injected into the muscle, not the fat.

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Researchers found similar problems with the hepatitis A vaccine, and other studies have found significant drops in antibody protection induced by tetanus and rabies vaccines in obese people.

“Obesity is a serious global problem, and the vaccine-induced suboptimal immune responses seen in the obese population cannot be ignored,” researchers from the Mayo Clinic Vaccine Research Group argued in a study. of 2015 published in the journal Vaccine.

Vaccines are also known to be less effective in older people, which is why people 65 years of age and older receive an annual supercharged influenza vaccine that contains many more influenza virus antigens to help boost their response. immune.

In contrast, the reduced protection of the obese population – adults and children – has been largely ignored.

“I’m not quite sure why the vaccine’s efficacy in this population hasn’t been better reported,” said Catherine Andersen, assistant professor of biology at Fairfield University who studies obesity and metabolic diseases. “This is a missed opportunity for greater public health intervention. “

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In 2017, scientists at the University of North Carolina – Chapel Hill provided a critical clue about the limitations of the influenza vaccine. In an article published in the International Journal of Obesity, researchers showed for the first time that obese vaccinated adults were twice as likely to develop the flu or flu-like illness compared to adults of a healthy weight.

Oddly enough, the study found that obese adults produced a protective level of antibodies against the flu shot, but these adults still responded poorly.

“It was the mystery,” said Chad Petit, influenza virologist at the University of Alabama.

One hypothesis, Petit said, is that obesity can trigger metabolic deregulation of T cells, white blood cells essential for the immune response. “It’s not insurmountable,” said Petit, who is researching Covid-19 in obese patients. “We can design better vaccines that could overcome this gap. ”

Historically, people with a high BMI have often been excluded from drug trials because they frequently suffer from chronic conditions that could obscure the results. Ongoing clinical trials to test the safety and efficacy of a coronavirus vaccine do not include a BMI exclusion and will include obese people, said Dr Larry Corey, of the Fred Hutchinson Cancer Research Center , which oversees Phase III trials sponsored by the National Institutes of Health.

While the trial coordinators don’t specifically focus on obesity as a potential complication, Corey said participants’ BMIs will be documented and results evaluated.

Dr Timothy Garvey, endocrinologist and director of diabetes research at the University of Alabama, was among those who pointed out that, despite lingering questions, it is still safer for obese people to get vaccinated. .

“The flu vaccine still works in obese patients, but not as well,” Garvey said. “We still want them to get vaccinated. “

KHN (Kaiser Health News) is a non-profit news service covering health issues. This is an independent editorial program of KFF (Kaiser Family Foundation) which is not affiliated with Kaiser Permanente.

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