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Explained: Two vaccine doses highly effective across people of different body weights, study suggests

A new study published in The Lancet Diabetes and Endocrinology has found that body size was not a factor in the effectiveness of vaccines — two doses are highly effective against severe disease for people who are underweight, overweight, or who have obesity.

Written by Anuradha Mascarenhas | Pune |
Updated: July 2, 2022 8:22:24 am
A woman receives the Moderna vaccine during a COVID-19 vaccination at the Isabel Zendal Hospital in Madrid, Spain. (AP)

Obesity has been identified as a risk factor for severe Covid-19 since early in the pandemic, but little was known until now about the effectiveness of the vaccines for people with obesity. Now a new study published in The Lancet Diabetes and Endocrinology has found that body size was not a factor in the effectiveness of vaccines — two doses are highly effective against severe disease for people who are underweight, overweight, or who have obesity. In fact, the benefits were found to be slightly lower among underweight people compared to people with higher body mass index (BMI).

The sample

This is the largest study of BMI and Covid-19 vaccine effectiveness. Carried out in the UK, it covered 9,171,524 adult patients who had BMI data and had not previously been infected with SARS-CoV-2. They were grouped based on their BMI: healthy weight, underweight, overweight and obesity. During the study period from December 8, 2020 (date of the first vaccine given in the UK) to November 17, 2021, over 5.6 lakh of the 9 million participants tested positive. Of those, 32,808 were admitted to hospital and 14,389 died.

At the end of the study period, 23.3% of the healthy weight group, 32.6% of the underweight group, 16.8% of the overweight group and 14.2% of the group with obesity had not received any dose of any vaccine.

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The researchers compared risk of severe disease in vaccinated versus unvaccinated people at least 14 days after a second dose. They found that being vaccinated offered high protection across all BMI groups, but the effect differed slightly in different BMI groups.

The findings

* In the underweight group, vaccinated people had around half the likelihood of being hospitalised or dying compared with unvaccinated people.

* In the healthy and high BMI groups, the vaccinated people were 70% less likely to be hospitalised than those unvaccinated, and two-thirds less likely to die those not vaccinated.

* Among vaccinated people only, of the fewer Covid-19 cases recorded, people of very low and very high BMI were more likely to experience severe disease. For example, following two doses, a BMI of 17 was linked to a 50% increase in risk of hospitalisation compared with a healthy BMI of 23, and a very high BMI of 44 had three times the risk of hospitalisation compared with a healthy BMI.

Takeaway for underweight

“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,” lead author Dr Carmen Piernas of the Nuffield Department of Primary Care Health Sciences, University of Oxford, said in the report.

In a linked comment, Professor Annelies Wilder-Smith and Professor Annika Frahsa of the University of Berne (who were not involved in the study) wrote: “There was a higher vaccine uptake by persons with obesity… These findings should prompt a shift towards more targeted and differentiated public health messaging to also address underweight persons who may perceive themselves at lower risk in order to enhance vaccine uptake in this group.”

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The study was found by the UK Research and Innovation and National Institute for Health Research Oxford Biomedical Research Centre.

Obesity as a risk factor

One in five individuals worldwide are at increased risk of severe clinical outcomes after SARS-CoV-2 infection due to underlying health conditions, and there is now consistent evidence showing that obesity is a significant independent risk factor, according to the report. While the cause of the increased risk among people with obesity is unknown, there are several plausible explanations. These include fat deposited around the airways that could reduce functional lung capacity, obesity-related conditions that could exacerbate the pathology of Covid-19, higher viral load and prolonged and increased viral shedding that could affect recovery time, as well as factors that could impair T cell function. In addition, fat in the chest wall and abdomen in people with obesity could make ventilation more difficult, airways more prone to collapse, and could require higher pressures to maintain airways, which can lead to increased ventilation-induced damage.

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First published on: 01-07-2022 at 09:28:01 pm
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