Severely obese people may need more frequent COVID-19 booster shots to keep their immunity going, new research suggests.

Protection from the shots declines more rapidly in those who are severely obese compared to those at a normal weight, according to scientists at the Universities of Cambridge and Edinburgh in the United Kingdom.

“Because of the high prevalence of obesity across the globe, this poses a major challenge for health services,” study co-author Sadaf Farooqi said in a Cambridge news release. She is from the Wellcome-MRC Institute of Metabolic Science at Cambridge.

Past research has shown that COVID vaccination has been highly effective at reducing symptoms, hospitalization and death, including for people with obesity. Yet antibody levels may be lower in vaccinated obese people, potentially putting them at higher risk of severe disease and death, the researchers noted.

To study this, a team from the University of Edinburgh, led by Aziz Sheikh, assessed data tracking the health of 3.5 million Scottish people as part of the EAVE II study.

Specifically, they looked at hospitalization and death from COVID-19 in adults who received two doses of either the Pfizer-BioNTech mRNA vaccine or the AstraZeneca vaccine. (The AstraZeneca vaccine is not offered in the United States.)

Those with a body mass index (BMI) greater than 40 — considered extreme obesity — had a 76% higher risk of severe COVID-19 outcomes, compared to those with a normal BMI. A modest increase in risk was also seen in people whose BMI was 30 to 39.9, considered to have obesity rather than severe obesity, and those who were underweight.

People with severe obesity had break-through infections after the second vaccine dose sooner (from 10 weeks), than those with obesity (from 15 weeks) and those with a normal weight (20 weeks), the study found.

“Our findings demonstrate that protection gained through COVID-19 vaccination drops off faster for people with severe obesity than those with a normal body mass index,” Sheikh said.

Meanwhile, a University of Cambridge team studied hospital patients in Cambridge, comparing the number and function of immune cells in their blood to those of people of normal weight.

Six months after a second vaccine dose, people with severe obesity had similar levels of antibodies to COVID-19 as those with a normal weight.

However, the ability of those antibodies to work efficiently to fight the virus was reduced in people with obesity. About 55% of people with severe obesity had unquantifiable or undetectable “neutralizing capacity” compared to 12% of people with normal BMI, the investigators found.

After a third vaccine dose, the ability of the antibodies to neutralize the virus was restored in both the normal weight and severely obese individuals. Immunity once again declined more rapidly in those who were severely obese.

“It is promising to see that booster vaccines restore the effectiveness of antibodies for people with severe obesity, but it is concerning that their levels decrease more quickly,” said co-author Dr. James Thaventhiran, a group leader from the MRC Toxicology Unit in Cambridge. “This shows that the vaccines work as well in people with obesity, but the protection doesn’t last as long.”

The study findings were published May 11 in the journal Nature Medicine.

More information

The U.S. Centers for Disease Control and Prevention has more on obesity and COVID-19.

SOURCE: University of Cambridge, news release, May 11, 2023