A growing body of evidence suggests that vaccines may be less effective in people with obesity. However, a new study published Monday found that delivering vaccines nasally or orally might help obese patients mount a stronger immune response. Although the study was conducted in mice, it adds to growing evidence that obesity alters how the immune system responds to both vaccination and infection.
Researchers at the University of Missouri and the University of Maryland tested an experimental nasal vaccine targeting Pseudomonas aeruginosa — a bacterium that causes urinary tract, bloodstream, lung and wound infections — in mice fed low-fat, normal or high-fat diets. While all of the animals generated an immune response after vaccination, the mice fed a high-fat diet — used to model obesity in humans — produced fewer antibodies, the proteins the body uses to identify and target pathogens.
While obese mice produced fewer antibodies, they generated other immune cells that could help compensate for the reduced response, Wendy Picking, the study’s senior author, told Straight Arrow News.
Higher risk, poorer protection
Over the past decade, large population studies have consistently found that people with obesity are more likely to contract certain infectious diseases — including the flu, pneumonia, skin infections and COVID-19. They are also at a higher risk of severe illness, hospitalization and death from those diseases.
One recent analysis published in March estimated that obesity contributed to roughly 1 in 10 deaths from infectious diseases worldwide; that rate rose to 1 in 7 during the pandemic. The same study estimated that people with obesity were 70% more likely to be hospitalized or die from an infection.
Researchers believe the increased risk is due to overlapping factors. Obesity is linked to chronic, low-level inflammation that can hinder normal immune system functioning. Obesity may also affect how immune cells communicate while they are mounting a defense against an invader. Excess weight may also restrict lung expansion and lower respiratory volumes, making it harder for the lungs to clear infections.
In addition, studies like Picking’s show that the protection from vaccines is less robust and less durable in people with obesity.
Researchers have found that while obese individuals mount a strong initial immune response after vaccination, that protection — in the form of antibodies — fades more quickly, leaving them at higher risk of becoming sick later on.
But Picking’s study added another dimension: While the part of the immune system that produces antibodies was not as robust in obese mice, another part of the immune system that produces killer T cells — which directly attack and eliminate cells infected by viruses and bacteria — was still active. T cells can circulate through the whole body in the blood, but some cells stay in specific tissues. In Picking’s study, the obese mice had comparable levels of T cells in their lungs and might compensate for low antibody production, Pickings said.
A rising epidemic
U.S. obesity rates have more than tripled since the 1970s, according to the Centers for Disease Control and Prevention. Today, roughly 40% of adults and just over 20% of children and teenagers in the U.S. are obese.
In December, the World Health Organization estimated that obesity caused nearly 4 million deaths worldwide, many due to chronic conditions such as cardiovascular disease.
Vaccines still offer some protection — and are still recommended — for people with obesity.
Picking said her team’s findings highlight the need to better understand how vaccines perform across different populations — and could encourage the development of vaccines that provide stronger, longer-lasting protection for people with obesity, older patients and other immunocompromised individuals. While oral and nasal vaccines may offer a promising alternative to intramuscular injections, few are currently in use, and existing options — such as the nasal flu vaccine — have had limited consumer uptake.