Healthy diet impacts flu vaccine effectiveness
The researchers note that obesity is associated with a higher risk of severe infectious diseases, including the flu.
While this heightened risk makes it more critical for this group to get vaccinated, researchers note that obesity can also decrease the effectiveness of flu vaccines.
For the study, they tested a few different scenarios to see if dietary changes helped prior to and after vaccination.
They took two groups of mice and fed one group a lean diet and the other a high fat diet . The mice then received a flu vaccine. After vaccination, some mice that were on the high fat diet were switched to the control diet. Mice then received a lethal dose of the flu virus, homotypic H1N1, after either 4 weeks or 12 weeks on the control diet.
Researchers found that switching to a healthy diet post-vaccination did not improve survival despite the weight loss that the previously obese mice experienced.
The previously obese mice had only a 24% survival rate after 4 weeks on the control diet and a 28% survival rate after 12 weeks on the control diet. However, the results suggested that dietary changes to lose weight after vaccination may help control viral spread.
The results were much different when the dietary changes were made pre-vaccination. To test this, researchers had certain obese mice switch to the lean control diet 4 weeks before vaccination. This switch allowed for several systemic measurements of metabolic dysfunction to return to normal and for weight loss to occur.
Researchers observed an improved immune response in these mice, particularly among their T cells, and decreased morbidity and mortality.
After exposure to the flu virus, the formerly obese mice had a 100% survival rate. The results suggest that specific dietary changes and weight loss may help improve the flu vaccine’s effectiveness.
The research also adds to what we know about how obesity may impact immune response, which will be an area for continued research.
“We have known since the 2009 H1N1 flu epidemic that people with obesity are at increased risk of severe flu and death, and we have seen similar findings with COVID-19. It is not entirely clear why, however — it could be decreased lung function and/or other factors,” non-study author Marci Drees, MD , chief infection prevention officer and hospital epidemiologist for ChristianaCare, told Medical News Today .
“It’s important to remember that this study was conducted in mice, and of course, mice are not humans — so it is certainly not definitive in terms of proving that people with obesity don’t respond as well to flu vaccines,” Drees said.
Effects of metabolic health on vaccine response not fully understood
The study’s main limitation is that it was conducted in mice, meaning further investigation is needed before these findings could be applied to humans.
Researchers also note they were limited in their ability to determine certain factors, as they had a low sample size of mice on the high fat diet who survived exposure to the flu. They acknowledge the need for a more in-depth investigation of how nutrition affects immune cell function during vaccination and infection.
“There have been some small studies in the past that showed that people with obesity were more likely to get the flu, even if vaccinated, compared to vaccinated people who were not obese — and despite having good levels of antibodies against the flu strains in the vaccines that year,” Drees said.
“There is a lot more that needs to be studied in this area to better understand the interactions between obesity, the flu virus, and the flu vaccine.”
Non-study author Dr. Linda Yancey , director of infection prevention at the Memorial Hermann Health System in Houston, noted the following to MNT :
“First off, this is a mouse study. It goes without saying that mice are not people. This looks like a nice foundational study to base future human trials on. Studies like these are more important than many people give them credit for because they prove something that everyone generally agrees upon — a healthy diet and weight loss are good for you. While we all believe this to be true, it is nice to see solid scientific data backing this up.”
Will obesity impair the flu vaccine response?
The findings demonstrate that a healthy diet could affect vaccine effectiveness, but this doesn’t mean that people with obesity should avoid vaccination.
As the Centers for Disease Control and Prevention (CDC)Trusted Source notes, people with a body mass index (BMI) of 40 or higher can be at an increased risk for flu complications . Thus, vaccination might be even more important in this demographic.
People can talk with their doctors about personal risk factors that may increase complications if they get sick with the flu . They can also discuss any potential risks from the vaccine itself and how effective the vaccine may be for them.
While the study won’t lead to immediate change in clinical practice or recommendations, weight loss among individuals who are obese is generally encouraged by healthcare professionals.
“[The study] will need to be followed up by a human trial to see if the observation holds up,” Yancey noted.
“If so, then we could potentially recommend a healthy diet and weight loss in the weeks leading up to vaccination. However, this is a general recommendation for everyone already. So, there wouldn’t be any big changes in overall health advice.”
Dress said she wouldn’t change any current recommendations based on this one study in mice, noting the following:
“There are many health benefits to losing weight , and [a] better response to vaccines might be one of them. But that is really just a theory right now. I definitely would still highly promote influenza vaccine regardless of your weight — and I would probably recommend it even more highly in persons with obesity because we know their risk of severe flu is higher.
So, I wouldn’t want someone to not get vaccinated because they think the flu vaccine won’t work for them — there is also good evidence that even if you get the flu after being vaccinated, your risk of severe disease and death is lower. Persons living with obesity should discuss with their doctor what their options are for weight loss, but should still definitely get their annual flu shot .”
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