New Delhi: Covid-19 vaccines brought down cases of severe disease for everyone, irrespective of their body size, according to a study published Friday in The Lancet Diabetes & Endocrinology. The study evaluated vaccine efficacy among people with different Body Mass Index (BMI) scores — the measure of body fat based on height and weight.
The study by researchers at the universities of Oxford, Leicester, and Nottingham in the UK found that vaccine effectiveness was similar for those with a higher BMI and those in the healthy weight group, but slightly lower in the underweight group.
People were grouped based on their BMI according to World Health Organization’s definitions. The WHO categorises people with a BMI in the range of 18.5-24.9 kg/m2 as having a healthy weight, while those below 18.5 kg/m2 are underweight. Those in the 25-29.9 kg/m2 range are overweight, while a BMI of 30 kg/m2 or higher is obese.
For this study, researchers compared the risk of severe disease in unvaccinated and vaccinated people (at least 14 days after the second dose) and found that being vaccinated offered high protection across all BMI groups, but that the effect was slightly lower among underweight people.
The study used anonymised data from UK health records, and did not specify which vaccines the patients had taken.
Underweight vaccinated people were 50 per cent less likely to be hospitalised or die of severe disease compared to unvaccinated people with the same BMI. Meanwhile, vaccinated people in the healthy and high BMI groups were around 70 per cent less likely to be hospitalised than unvaccinated people.
“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,” said Carmen Piernas, a researcher at the University of Oxford in the UK and one of the authors of the study.
“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,” he added.
Over 12 million records examined
Experts pointed out that obesity is one of the risk factors linked to severe Covid-19 in the early phases of the pandemic. As a result, countries like the UK prioritised people with a BMI of over 40, declaring them a high-risk group for vaccination programmes.
However, according to researchers, little was known about the effectiveness of the Covid-19 vaccines for people with obesity.
For this study, the researchers examined the anonymised health records of more than 12 million (1.2 crore) patients treated by 1,738 general practitioners in England who took part in QResearch — a secure database of healthcare information available to verified researchers.
Of these, 9,171,524 (over 18 years old) patients with BMI data who had not previously been infected with SARS-CoV-2 were included in the study.
Of the more than nine million people included in the study, 566,461 tested positive for Covid-19 during the study, between 8 December 2020 and 17 November 2021. Of those, 32,808 were admitted to a hospital and 14,389 succumbed to the infection.
At the end of the period of the study, 23.3 per cent in the healthy weight group, 32.6 per cent in the underweight group, 16.8 per cent in the overweight group and 14.2 per cent in the group with obesity, had not received any doses of a Covid-19 vaccine.
The vaccine was similarly effective in reducing the risk of severed disease people with a healthy BMI and those with a high BMI, compared to their unvaccinated counterparts. In absolute terms, however, the study found that individuals with a high BMI — who face a higher risk to begin with — were still more at risk after vaccination than those with a low BMI.
The cause of increased risk among people with obesity is unknown; the researchers speculated that their findings may be explained, in part, by an altered immune response in heavier individuals.
The reduced effectiveness of Covid-19 vaccines among people with a low BMI may also reflect a reduced immune response as a consequence of frailty or other conditions associated with low body weight, according to the researchers.
They added that further research is needed to explore the relationship between BMI and immune responses.
(Edited by Amrtansh Arora)