Pfizer vaccine may be less effective in people with obesity, says study

Linda Geddes Science correspondent
·3 min read
Photograph: Song Kyung-Seok/AP
Photograph: Song Kyung-Seok/AP

The Pfizer/BioNTech vaccine may be less effective in people with obesity, data suggests.

Italian researchers have discovered that healthcare workers with obesity produced only about half the amount of antibodies in response to a second dose of the jab compared with healthy people. Although it is too soon to know what this means for the efficacy of the vaccine, it might imply that people with obesity need an additional booster dose to ensure they are adequately protected against coronavirus.

Related: Obesity increases risk of Covid-19 death by 48%, study finds

Previous research has suggested that obesity – which is defined as having a body mass index (BMI) over 30 – increases the risk of dying of Covid-19 by nearly 50%, as well as increasing the risk of ending up in hospital by 113%.

Watch: High Number of Antibodies After Two Doses of Pfizer Vaccine

Some of this may be because people with obesity often have other underlying medical conditions, such as heart disease or type 2 diabetes, that increase their risk from the coronavirus, but excess body fat can also cause metabolic changes, such as insulin resistance and inflammation, which make it harder for the body to fight off infections.

This constant state of low-grade inflammation can also weaken certain immune responses, including those launched by the B and T cells that trigger a protective response following vaccination. Separate research has shown that the flu vaccine is only half as effective in people with obesity compared to those who are a healthy weight.

The new study, which has not yet been peer reviewed, provides the first direct evidence to suggest a similar problem might occur with Covid-19 vaccines.

Aldo Venuti, of the Istituti Fisioterapici Ospitalieri in Rome, and his colleagues assessed the antibody response following two doses of the Pfizer/BioNTech vaccine in 248 healthcare workers. Seven days after receiving the second dose, 99.5% of them had developed an antibody response, and this response was greater than that recorded in people who had recovered from Covid-19. However, the response was blunted in people who were overweight and obese.

“Since obesity is a major risk factor for morbidity and mortality for patients with Covid-19, it is mandatory to plan an efficient vaccination programme in this subgroup,” Aldo and his colleagues wrote. “Although further studies are needed, this data may have important implications to the development of vaccination strategies for Covid-19, particularly in obese people. If our data was to be confirmed by larger studies, giving obese people an extra dose of the vaccine or a higher dose could be options to be evaluated in this population.”

“We always knew that BMI was an enormous predictor of poor immune response to vaccines, so this paper is definitely interesting, although it is based on a rather small preliminary dataset,” said Danny Altmann, a professor of immunology at Imperial College London. “It confirms that having a vaccinated population isn’t synonymous with having an immune population, especially in a country with high obesity, and emphasises the vital need for long-term immune monitoring programmes.”

In a separate study of Brazilian healthcare workers, Altmann and his colleagues showed that reinfection with Sars-CoV-2 was also more common among people with a high BMI, and that they tended to have lower antibody responses to the original infection.

Watch: Pfizer vaccine is 94% effective in real-world study