Weight and COVID-19 Immunity: Vaccination vs. Infection

A recent study found that excess weight affects how the immune system responds to COVID-19,
showing differences between post-infection and post-vaccination immunity. Led by Marcus Tong from
the University of Queensland, the research suggests that being overweight, not just obese, makes SARS-
CoV-2 infections more severe and changes the immune response.
In a unique study group infected at the beginning of the pandemic, blood samples were taken three and
13 months after infection. Those with a higher body mass index (BMI) experienced a faster decline in
immune response, especially against certain variants. Interestingly, vaccinated individuals did not show
this decline, highlighting the potential superiority of vaccine-induced protection for overweight people.
The study included participants who remained uninfected and unvaccinated for 13 months, allowing
researchers to isolate the effects of natural protection versus vaccination. Five months after their
second vaccine dose, participants who had never had COVID-19 were included. Regardless of BMI, no
significant differences in immunity were found in this vaccinated group.
The study emphasizes the importance of vaccination for overweight individuals, as their infection risks
and weakened immune responses may increase the chances of reinfection. Dr. Kirsty Short from the
University of Queensland stresses the crucial need for vaccination in this group.
However, for those with severe obesity (BMI > 40 kg/m2), a separate study in Nature Medicine in May
2023 showed a different scenario. Despite initially similar vaccine responses between obese and
healthy-weight individuals, those with severe obesity experienced a quicker decline in immunity
effectiveness, leading to more hospitalizations and deaths.
While a third vaccine dose restored immunity in severe obesity cases, it declined faster afterward. The
study authors suggest considering more frequent COVID-19 vaccinations for people with severe obesity
to ensure they have protection comparable to those with a normal BMI, considering the widespread
prevalence of obesity globally.

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