Fat or thin, the anti-Covid vaccine does not discriminate. Its effectiveness in preventing severe forms of the infection does not change, or at least not by much, regardless of a person’s body mass index (BMI). However, it seems to work slightly less in underweight people, the same people who in the UK have not adhered to the anti-Covid vaccination campaign. These are the not so obvious conclusions of a careful analysis conducted by the University of Oxford and published in the journal The Lancet Diabetes & Endocrinology.
Obesity as a risk factor for Covid
At the beginning of the pandemic, obesity was immediately identified as a risk factor for severe forms of Covid-19 and that is why, both in Italy and in other countries of the world, obese people were included among the categories at risk with priority access to vaccines, which at the time were few in number. However, little was known about the effectiveness of Covid vaccines in people with obesity.
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Previous research has shown that obese people are less likely to get the flu shot, which however appears to have slightly reduced effects on them. But with Covid vaccines, things look different. “Our findings provide further evidence that Covid-19 vaccines save the lives of people of all sizes,” says the study’s lead author. Carmen Legs of the Nuffield Department of Primary Care Health Sciences, University of Oxford.
The analysis on 12 million medical records
To reach these conclusions, the researchers analyzed the medical records of more than 12 million British patients registered on QResearch, a repository of health information available to researchers. The researchers’ attention then focused on 9,171,524 patients over the age of 18, who had not previously been infected with Sars-CoV-2.
In addition to the BMI, other characteristics were also taken into consideration, such as 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 during the study, from 8 December 2020 (date of the first vaccine administered in the UK) to 17 November 2021. these, 32,808 were hospitalized and 14,389 died. At the end of the study period, 23.3 percent of the healthy body weight group, 32.6 percent of the underweight group, 16.8 percent of the overweight group and 14.2 had received no vaccines. % of the group with obesity.
The findings on severe disease protection
To understand the vaccine‘s effectiveness, the researchers compared the risk of serious illness in vaccinated versus unvaccinated people. Well, scientists have found that being vaccinated offers high protection to all people, regardless of BMI. “Our results reassure people with obesity – Piernas points out – that Covid-19 vaccines are just as effective for them as they are for people with a lower BMI and that vaccination substantially reduces the risk of serious illness if infected with Covid. 19 “.
An important message for the population suffering from obesity. “Especially considering that unvaccinated obese people over 60 years of age are 6 times more likely to develop severe Covid-19 and thus die,” he adds. Marco Chianellicoordinator of the Obesity and Metabolism Commission of the Medical Endocrinologists Association (AME).
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Small decline in efficacy in underweight people
However, the effect of the vaccine was slightly lower in underweight people. More precisely, vaccinated underweight people would be about half as likely to be hospitalized or die as unvaccinated people with the same BMI.
“This could depend on the immune system that in underweight people, often malnourished or in any case with some deficiency syndrome, could respond less energetically to vaccine solicitations”, explains Chianelli.
The researchers then went deeper. Looking only at the data of vaccinated people (among which the number of Covid-19 cases was significantly reduced), people with a higher Bmi or, on the other side, with a lower Bmi had a higher risk of developing a serious disease. compared to those with a healthy BMI. For example, a BMI of 17 was linked to a 50% increase in hospitalization risk compared to a healthy BMI of 23, and a very high BMI of 44 was three times more at risk of hospitalization than a healthy BMI.
Data consistent with those of the flu
The cause of the increased risk among people with obesity is still unknown, but it is consistent with the higher rate of seasonal flu infections found in people with a higher Bmi. The authors speculate that the results of their study may be explained, in part, by an altered immune response in overweight individuals. Instead, the reduced effectiveness of Covid-19 vaccines among people with low Bmi may also reflect a reduced immune response as a result of frailty or other conditions associated with low weight.