The First Direct Evidence That Obesity Impairs COVID-19 Vaccine Effectiveness

Being obese has been found to be associated with a nearly 50% increased risk of dying from COVID-19, and can also make you over twice as likely to need hospitalisation should you become infected. This is partly because obese individuals are more likely to suffer from other conditions that make COVID-19 more threatening, such as heart disease and type II diabetes. However, fat tissue can also produce inflammatory signals which, over time, can weaken the adaptive immune system: the T and B cells that are so important when it comes to developing immunity against a pathogen.

Now, a relatively small study that has not yet been peer reviewed suggests that obesity may hamper vaccine-induced immunity to COVID-19. The study measured the antibody response following the second dose of the Pfizer/BioNTech vaccine in 248 healthcare workers in Italy. Over 99% of participants developed an antibody response. However, that response was found to be weaker in those with a higher Body Mass Index (BMI):

A strong correlation of BMI classes with antibody titres was noticed: humoral response was more efficient in the group with under- and normal weight vs the group with pre- and obesity participants (p<0.0001 at T1).

This result is not particularly surprising, as we have known since long before COVID-19 that high BMI is associated with a poor vaccine response. The flu vaccine, for example, is only around half as effective in overweight individuals compared to those with a healthy weight. We also have evidence to suggest that obese individuals form weaker antibody responses to COVID-19, and are more likely to be re-infected.

While this outcome was predictable, we can still benefit from taking note. This study highlights the fact that vaccination doesn’t guarantee complete immunity, especially if you have a high BMI. It has implications for vaccine rollouts – it may be beneficial to give obese people an additional dose. It also means that population immunity as a whole is likely to be lower in countries with high obesity.

With all this being said, it is still no less essential for overweight individuals to get vaccinated, as partial protection is a lot better than no protection at all. Indeed, due to the increased risk that comes with being obese, those with a high BMI are still likely to benefit more from vaccination than a lean person, all other risk factors being equal.