How Does Obesity Affect COVID-19 Vaccine Immunity?

New research is shedding light on how the COVID-19 pandemic could be intensified by another ongoing public health concern: the obesity epidemic.

It's known that obesity can increase your risk of severe illness if you catch COVID-19, but does that also mean your weight could affect how well a vaccine can protect you from the virus?

Verywell asked several experts whether it's possible that the Pfizer and Moderna COVID-19 vaccines may not work as well in people who are overweight and obese.

Obesity: A Risk Factor for COVID-19

The Centers for Disease Control and Prevention (CDC) lists obesity as a risk factor for severe COVID-19 illness, hospitalization, and death.

Aaron Eli Glatt, MD, FACP, FIDSA, FSHEA, the chair in the Department of Medicine and chief of Infectious Diseases and Hospital Epidemiologist at Mount Sinai South Nassau, tells Verywell that according to the CDC's guidance, people with a body mass index (BMI) between 35 and 40 have a very severe risk for COVID-19. Even BMIs over 25 are considered high-risk.

An August 2020 study in Obesity Reviews found that compared to people who were not obese, people considered obese:

• Had a 46% increased risk for COVID-19 infection
• Were 113% more likely to be hospitalized with a COVID-19 infection

The study also found that there was a 74% increase in the number of deaths from COVID-19 in people who were obese compared to people who were not obese.

How Obesity Increases Risk

According to a study published in the journal Diabetes, Obesity, And Metabolism in September 2020, obesity’s role in increased mortality rates might be more prevalent in women than in men.

The COVID-19 pandemic itself might also be contributing to rising rates of obesity. A July 2020 article in Nature Reviews Endocrinology reported that emotional distress—with potential triggers being a declining economy, mandated lockdowns, and fear of infection—can prompt the brain to "emotionally eat" as a coping mechanism.

Obesity is multifactorial and can impact a person in many different ways. For one, excess weight can impair your breathing and the ability to take deep breaths. Nitin Desai, MD, CEO and CMO of COVID PreCheck, tells Verywell that it is challenging for people with obesity to be intubated and put on a ventilator because of their neck anatomy.

Desai also says that people who are obese often have other underlying health conditions as well. One example is sleep apnea, which can cause low oxygen and pulmonary hypertension in severe cases. Obesity also increases the risk of other health conditions that can compromise immunity, like diabetes mellitus and heart disease.

Obesity and Immunity

Desai says that obesity has recently been recognized as a chronic disease rather than the state of a person’s weight. As with other chronic illnesses such as cancer, obesity can contribute to low resistance to infections.

“Adipose fat is considered like an endocrine organ now, and the immune response in central obesity is that the fat that sits around the organ and abdomen has a much higher prevalence of low immunity in fighting infection and generating antibodies to vaccines,” Desai says.

A 2012 review in the Proceedings Of The Nutrition Society reported that a potential mechanism could be that excess fat hinders access to the nutrients that immune cells need to carry out their daily activities.

How Vaccination Is Affected

Research has shown that obesity’s role in an impaired immune system often shows itself as lowered vaccine effectiveness. A 2017 study in the journal Annals of the American Thoracic Society found that adults with obesity who were vaccinated with the flu shot were two times more likely to get sick than vaccinated adults who were not obese—despite having the same level of vaccine-induced antibodies. The researchers theorized that the effect might be related to impaired T cell function.

“The data we have so far is from influenza, hepatitis B, and tetanus that shows people who are obese have a decreased immune response to those vaccines,” Desai says.

The Bottom Line

In terms of the new COVID-19 vaccines, Glatt says that there’s no evidence that the mRNA vaccines produced by Moderna and Pfizer would not work in a person who is obese. Rather, Glatt thinks that there are not enough studies to show how well the vaccine works in people who are overweight or obese.

The data that has been released by the U.S. Food and Drug Administration (FDA) and Pfizer show that the clinical trial was representative of people at different body weights—34.8% of vaccinated participants and 35.3% of participants in the placebo group were obese.

“I think the evidence strongly supports that it is effective in obese patients, but I can’t guarantee that it’s as effective until we get a lot more data,” Glatt says.

Unlike the annual flu shot that uses a weakened or inactive version of the influenza virus, Pfizer and Moderna's COVID-19 vaccines use mRNA technology. Desai says that this changes how the immune response is generated.

However, Desai personally thinks that people who are obese will still respond poorly to the COVID-19 virus because of the body’s inability to handle the infection.

“It’s not how the immune challenge is administered whether through a vaccine or natural disease. The body’s response is weak irrespective of how the challenge is dealt,” Desai says. “People with obesity are most likely going to respond poorly whether it’s the vaccine or the virus. The coronavirus has already proven that it’s not good for obese individuals. In my opinion, no scientific evidence on this yet, [but] the vaccine will work more poorly in obese individuals.”

By that logic, boosting your chances for vaccine effectiveness means controlling for obesity—but Glatt admits that's easier said than done. “It’s a hard thing to accomplish, but it’s an important thing to accomplish.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.