Oxford, UK—People who are overweight or obese are at risk for more severe effects from COVID-19, but larger body size did not appear to matter much in the ability of vaccines to significantly decrease cases of severe COVID-19 disease.

An article published in The Lancet Diabetes & Endocrinology found vaccine effectiveness to be similar for recipients with a higher BMI and those with healthy weight, but slightly lower in the underweight group, who were also the least likely to have been vaccinated.

UK researchers from the University of Oxford noted that with further analysis of vaccinated people only, not many COVID-19 cases were recorded; however, vaccine recipients of very low and very high BMI were more likely to suffer severe disease than the general vaccination cohort.

Early in the COVID-19 pandemic, obesity was found to be a risk factor for severe illness and, in the UK, people with a BMI over 40 were prioritized for vaccination.

"However, little was known until now about the effectiveness of the COVID-19 vaccines for people with obesity," the authors wrote. "Previous work has shown that people with obesity are less likely to take seasonal flu vaccines and have modestly reduced benefits from flu vaccinations, although the reasons for this are not well understood."

For the study, researchers used anonymized health records from more than 12 million patients across 1,738 general practitioner practices in England taking part in QResearch—a secure database of healthcare information available to verified researchers. The study included approximately 9 million adult patients with BMI data and who had not previously been infected with SARS-CoV-2.

Participants were grouped based on their BMI according to four World Health Organization definitions:

• A BMI of 18.5 to 24.9 kg/m2 for healthy weight.
• A BMI below 18.5 for underweight; 25 to 29.9 for overweight.
• A BMI 30 and over as obesity with levels adjusted for Asians to reflect the higher health risks at lower BMI levels in this group.

The analysis also considered age, sex, smoking status, and social deprivation.

Of the more than 9 million people included in the study, 566,461 tested positive for SARS-CoV-2 from December 8, 2020 (the date of the first vaccine given in the UK) to November 17, 2021. Of the infected patients, 32,808 were admitted to the hospital and 14,389 died.

"Our findings provide further evidence that COVID-19 vaccines save lives for people of all sizes. 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," explained lead author Dr. Carmen Piernas of the Nuffield Department of Primary Care Health Sciences, University of Oxford, UK.

The results indicated that vaccine recipients in the healthy and high BMI groups were about 70% less likely to be hospitalized than unvaccinated people. People with a healthy or a higher BMI were also around two-thirds less likely to die than their unvaccinated counterparts 2 weeks after a second dose.

At the end of the study period, nearly one-fourth of the healthy weight group, one-third of the underweight group, 17% of the overweight group, and approximately 14% of the obese group had received COVID-19 vaccine doses.

In looking at the risk of severe disease by comparing the vaccinated and unvaccinated groups, the study team determined that being vaccinated offered high protection across all BMI groups, although the effect was slightly lower in underweight people. Researchers explain that underweight vaccinated people had about one-half the likelihood of being hospitalized or dying compared with unvaccinated people of the same BMI.

Putting it another way, the authors pointed out that a BMI of 17 was linked to a 50% increase in risk of hospitalization compared with a healthy BMI of 23, and a very high BMI of 44 had three times the risk of hospitalization compared with a healthy BMI.

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