2026-04-16

Influenza: a recombinant vaccine improves immune response in patients with severe obesity

Infectiology

By Elodie Vaz | Published on April 16, 2026 | 3 min read

A major viral infection, seasonal influenza is responsible each year for severe complications and hospitalizations, particularly among vulnerable populations. Among them, people living with severe obesity (defined as a BMI ≥ 35 kg/m²) represent a high-risk group that remains insufficiently characterized in vaccine trials.

In France, this condition affects around 6% of the adult population, i.e., more than three million individuals. Obesity is associated with an increased risk of severe influenza, partly due to chronic inflammation and alterations of the immune system. Several studies point to a reduced or less durable vaccine response in this population. Antibody titers measured after vaccination, particularly by hemagglutination inhibition (HAI), are generally correlated with the level of protection, although this relationship remains imperfect.

Improving vaccine immunogenicity

In this context, the French clinical study FLUO, published on March 19 and sponsored by AP-HP and coordinated by the F-CRIN networks “FORCE” and “I-REIVAC,” aims to determine whether a next-generation influenza vaccine could induce a superior immune response in adults with severe obesity.

The hypothesis is based on the use of a recombinant vaccine containing a higher amount of antigen—specifically hemagglutinin—and designed without the use of the whole virus. This technology is expected to enhance stimulation of the immune system.

The FLUO study included 206 adults recruited from 15 centers in France. Participants were randomized to receive either a standard influenza vaccine or a recombinant vaccine. The F-CRIN networks involved provide a national structure for the study: “FORCE” brings together 37 specialized obesity centers, while “I-REIVAC” has a reference network in vaccinology supported by 30 clinical centers and biological resource centers. The analysis focused on short-term (28 days) and medium-term (6 months) immunogenicity, as well as vaccine safety.

A short-term immune benefit

The results show that the recombinant vaccine induces a significantly higher immune response at 28 days for three of the four strains studied (A/H1N1, A/H3N2, B/Yamagata). No difference was observed for the B/Victoria strain.

However, this advantage disappears at six months, with no difference detected between the groups. This suggests a primarily short-term benefit, possibly related to a faster decline in immune response in individuals with severe obesity.

In terms of safety, no specific concerns were identified. Tolerability was comparable between the two types of vaccines. It should be noted, however, that FLUO is an immunogenicity study and therefore does not allow direct conclusions about clinical efficacy, particularly regarding prevention of infection or severe disease.

Toward more personalized vaccination

The findings of this research support the idea of adapting vaccination strategies for at-risk populations. As highlighted by Prof. Paul Loubet, lead author: “The FLUO results show that a one-size-fits-all approach to influenza vaccination in at-risk individuals is no longer appropriate. Adapting vaccination strategies, particularly through next-generation vaccines, is a concrete way to better protect them.”

At a time when the prevalence of obesity continues to rise globally, this study paves the way for a more personalized approach to vaccine prevention, taking into account patients’ immunological specificities. It also raises questions about the durability of the response and the potential need for adjustments, such as more frequent boosters or specific vaccine formulations.

Read next : Flu at school: what if it all began with education?

About the Author – Elodie Vaz
Health journalist, CFPJ graduate (2023).
Élodie explores the marks diseases leave on bodies and, more broadly, on human life. A registered nurse since 2010, she spent twelve years at patients’ bedsides before exchanging her stethoscope for a notebook. She now investigates the links between environment and health, convinced that the vitality of life cannot be reduced to that of humans alone.

Source(s) :
Recombinant vs Standard Influenza Vaccine in Adults With Severe Obesity: A Randomized Clinical Trial ;

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