A high BMI has been associated with a reduced immune response to influenza vaccination. Our objective was to investigate the association between BMI and COVID-19 vaccine uptake, vaccine effectiveness, and risk of severe COVID-19 outcomes after vaccination using a large representative population-based cohort from England. .
In this population-based cohort study, we used the database QResearch from general practice registries and included patients aged 18 years or older who were registered with a practice that was part of the database in England between 8 December 2020 (date of first vaccination in the UK), at November 17, 2021, with available data on BMI.
The acceptance it was calculated as the proportion of people with zero, one, two or three doses of the vaccine in all BMI categories. The effectiveness was evaluated through a nested matched case-control design to estimate odds ratios (ORs) for severe COVID-19 outcomes (i.e., hospital admission or death) in people who had been vaccinated against the than not, taking into account the dose and the time of the vaccine periods since vaccination.
Multivariate Cox proportional hazards models estimated the risk of severe COVID-19 outcomes associated with BMI (reference BMI 23 kg/m2) after vaccination.
Among 9,171,524 participants (mean age 52 [DE 19] years; BMI 26.7 [5,6] kg/m2), 566,461 tested positive for SARS-CoV-2 during follow-up, of whom 32,808 were admitted to hospital and 14,389 died. Of the total study sample, 19.2% (1,758,689) did not vaccinated, 3.1% (287,246) had one dose of vaccine, 52.6% (4,828,327) had two doses, and 25.0% (2,297,262) had three doses.
In people aged 40 years and older, acceptance of two or three doses of the vaccine was greater than 80% among people who were overweight or obese, which was slightly lower in people who were underweight (70–83%).
Although significant heterogeneity was found between BMI groups, protection against severe COVID-19 disease (comparing people who were vaccinated versus those who were not) was high after 14 days or more from the second dose for hospital admission (underweight: OR 0 51 [ IC 95% 0·41–0·63]; healthy weight: 0 34 [0·32–0·36]; overweight: 0 32 [0·30–0·34] and obesity: 0 32 [ 0,30–0,34]) and death (underweight: 0.60 [0,36–0,98]; healthy weight: 0.39 [0,33–0,47]; overweight: 0.30 [0 ·25–0·35] and obesity: 0 26 [0·22–0·30]).
In the vaccinated cohort, there were significant linear associations between BMI and COVID-19 hospitalization and death after the first dose, and J-shaped associations after the second dose.
Using BMI categories, there is evidence of protection against severe COVID-19 in people with overweight or obesity who have been vaccinated, which was of a magnitude similar to that of people with Healthy weight. The efficacy of the vaccine was slightly lower in people with under weightin whom vaccine acceptance was also the lowest for all ages.
In the vaccinated cohort, there were higher risks of serious outcomes from COVID-19 for people who were underweight or obese compared to the healthy-weight vaccinated population.
These results suggest the need for specific efforts to increase acceptance in people with a low BMI (<18.5 kg/m2), in whom acceptance is lower and the effectiveness of the vaccine appears to be reduced. Strategies to achieve and maintain a healthy weight should be prioritized at the population level, which could help reduce the burden of COVID-19 disease.
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