COVID-19 vaccines protected against severe disease and death in people with overweight or obesity, a large English study found.

Compared with the unvaccinated, vaccinated individuals in each BMI group experienced significantly lower likelihood of COVID-related hospitalization starting at 2 weeks from their second dose, reported Carmen Piernas, PhD, of the University of Oxford, and colleagues:

• Underweight: OR 0.51 (95% CI 0.41-0.63)
• Normal weight: OR 0.34 (95% CI 0.32-0.36)
• Overweight: OR 0.32 (95% CI 0.30-0.34)
• Obesity: OR 0.32 (95% CI 0.30-0.34)

Likewise, vaccinated people in all BMI groups also saw significantly greater protection against COVID-related death:

• Underweight: OR 0.60 (95% CI 0.36-0.98)
• Normal weight: OR 0.39 (95% CI 0.33-0.47)
• Overweight: OR 0.30 (95% CI 0.25-0.35)
• Obesity: OR 0.26 (95% CI 0.22-0.30)

But when comparing vaccinated BMI groups against each other, there was a J-shaped associated for severe COVID-19 after the second dose, meaning risk was higher for those with underweight (BMI below 18.5) and severe obesity (BMI of 40 or higher), the group wrote in Lancet Diabetes & Endocrinology.

Following a third dose, people in all BMI categories still had a significantly lower odds for severe COVID versus unvaccinated individuals, though there were very few cases reported.

“Our findings provide further evidence that COVID-19 vaccines save lives for people of all sizes,” Piernas said in a statement. “Our results provide reassurance to people with obesity that COVID-19 vaccines are equally as effective for them as for people with a lower BMI, and that vaccination substantially reduces their risk of severe illness if they are infected with COVID-19.”

“These data also highlight the need for targeted efforts to increase vaccine uptake in people with a low BMI, where uptake is currently lower than for people with a higher BMI,” she added.

To her point, only 70% to 83% of underweight adults ages 40 and older received two or three vaccine doses versus over 80% of those with overweight or obesity.

In an accompanying commentary, Annelies Wilder-Smith, MD, PhD, and Annika Frahsa, PhD, both of the University of Bern in Switzerland, said that this disparity with underweight individuals being less likely to be vaccinated “might have been an unintended result of public messaging that people with overweight have a higher risk of severe COVID-19, which was corroborated by the U.K. risk-based strategy of vaccine rollout.”

“These findings should prompt a shift towards more targeted and differentiated public health messaging to enhance vaccine uptake in people who are underweight and who might perceive themselves at lower risk of severe COVID-19,” they suggested.

The findings were based on 9,171,524 adults in the QResearch database. Vaccination data was collected between December 2020 and November 2021. Average age of the population was 52, and average BMI was 26.7. A total of 19.2% were unvaccinated, 3.1% had one vaccine dose, 52.6% had two doses, and 25.0% had three doses.

During this time period, 566,461 tested positive for COVID — 32,808 were admitted to hospital and 14,389 died.

The study utilized a matched case-control design, rather than negative-test case-control design — the type of study design that is recommended by the World Health Organization — which the researchers and the commentators both pointed out would’ve been a better method.

As for the findings among underweight individuals, Wilder-Smith and Frahsa pointed out that this data was limited by a lack of inclusion for certain confounding factors that would lead to underweight, like cancer or frailty.

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