Researchers examined the probability of serious illness in vaccinated versus unvaccinated individuals at least 14 days after a second dose in order to understand vaccination effectiveness.

London: A research of 90 lakh individuals in England, published on Friday in The Lancet Diabetes and Endocrinology, found that COVID-19 immunizations significantly decreased the number of instances of severe COVID-19 for everyone, independent of their body size.
The researchers found that vaccine efficacy was comparable for people with a higher body mass index (BMI) and healthy weight, but somewhat lower in the underweight group, who was also the group least likely to have received vaccinations.
People with very low and very high BMI were more likely to have the severe disease than people who had received the COVID-19 vaccine and were of a healthy weight, according to a subsequent examination of only vaccine recipients and the few COVID-19 cases that had been reported.

"Our findings provide further evidence that COVID-19 vaccines save lives for people of all sizes," said study lead author Carmen Piernas from the University of Oxford, UK.
"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," Piernas said.
The data also highlights 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, the researchers said.