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.
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.
