Researchers in Italy tested the presence of antibodies in people after two doses of the BNT162b2 jab separated by 21 days.
The subjects were 158 female and 90 male healthcare workers aged between 23 and 69, and all developed an immune response following inoculation.
Scientists noted a correlation between body mass index (BMI) and antibody presence, with subjects lower on the scale showing a stronger response. Younger people and women also had a higher concentration of antibodies.
More study is needed, the researchers said in the paper, which has not yet been peer-reviewed.
If the results were replicated by larger studies, it would be worth exploring the option of giving obese people bigger doses of the vaccine, researchers added.
They wrote: “The effectiveness of Covid-19 vaccines in people with obesity is a critical issue. Since obesity is a major risk factor for morbidity and mortality for patients with Covid-19, it is mandatory to plan an efficient vaccination program in this subgroup.
“Evidence suggests that SARS-CoV-2 infections are more severe and linger for about five days longer in people who are obese than in those who are lean.
“The constant state of low-grade inflammation, present in overweight people, can weaken some immune responses, including those launched by T cells, which can directly kill infected cells.
“Obesity is linked to less-diverse populations of microbes in the gut, nose and lung, with altered compositions and metabolic functions compared with those in lean individuals.
“Recently, researchers reported that changes of gut microbiome, by taking antibiotics, may alter responses to the flu vaccine. Moreover, vaccines against influenza, hepatitis B and rabies have shown reduced responses in those who are obese compared with those who are lean.
“To our knowledge, this study is the first to analyse Covid-19 vaccine response in correlation to BMI. Our data stresses the importance of close vaccination monitoring of obese people, considering the growing list of countries with obesity problems.”