Older people are more susceptible to flu and should therefore be vaccinated against influenza viruses. However, their immune system often does not develop sufficient immune protection against the pathogens after the vaccination. A detailed blood comparison now reveals why this is so. Accordingly, people who respond poorly to vaccinations lack certain molecules that are important for the immune response. According to the researchers, this could be due to a messenger substance in the blood that prevents an immune response. But diet also apparently plays a role in effective flu protection.
Autumn is here and with it comes the next flu wave. Influenza viruses are responsible for this infectious disease and can be particularly dangerous for older people. They are more likely to develop a severe course of the disease and end up in hospital with flu more often than younger people. The Robert Koch Institute therefore recommends a flu vaccination, especially from the age of 60.
There are also special flu vaccines for people in this age group that have higher doses than the standard flu vaccination, so-called high-dose vaccines. These are necessary because the immune systems of older people do not always respond sufficiently well to the standard flu vaccines. “With age, the immune system is obviously no longer able to mount such a powerful immune response,” explains senior author Yang Li from the Center for Individualized Infection Medicine (CiiM) in Hanover. But why is this the case and why doesn’t it apply to all older people?
Comparison of blood markers after flu vaccination
A team led by Li and first author Saumya Kumar from CiiM has now investigated which molecular processes are behind the reduced immune response in older people. In a study, the researchers vaccinated 234 participants over the age of 65 against influenza. In addition, they took blood from the test subjects at five different times before and after the vaccination and examined it for numerous immune markers. The team statistically evaluated the health data using computer models and compared the values of people with good and poor immune responses – so-called responders and low or non-responders.
The analysis identified several key molecules in the blood, including various receptors and messenger substances that ensure a strong immune response in the form of antibodies against influenza viruses during the flu vaccination. In non-responders, these molecules were present in significantly lower amounts in the blood than in responders. “We were able to identify a number of important molecules that correlated with the good immune response of responders after vaccination. In the non-responders, however, they were reduced or even non-existent,” explains Kumar.
The non-responders also had an increased number of natural killer cells in their blood. People who develop only low immune protection after a vaccination have fewer of the necessary signaling molecules and at the same time more “interfering” immune cells in their blood. This suggests a systemic dysregulation, i.e. a comprehensive malfunction of the immune system, as the team reports.
Can the immune response be predicted?
But can it be predicted before vaccination how good the immune response will be? Can it be checked in advance who actually needs a high-dose vaccine? To find out, the doctors compared the blood samples taken before and after the vaccination. And there were actually differences here too: “The later non-responders had increased levels of interleukin-15 before the vaccination,” reports Li. Subsequent experiments with mice suggested that this messenger substance prevents effective immune protection. “Interleukin-15 is obviously responsible for the lack of an immune response and could therefore be well suited as a predictive biomarker,” says Li. The doctors also found another difference in the blood of the non-responders: significantly lower concentrations of long-chain fatty acids. “Certain long-chain fatty acids have an anti-inflammatory effect and overall support the development of a good immune response,” explains Kumar.
In the future, the results could help to further increase the immune response to the flu vaccination in older people. To this end, further research will now be carried out into the newly identified key molecules that appear after vaccination or disrupt the vaccination reaction. According to the study, diet could be a quick-acting booster for immune protection against influenza viruses: “An adequate supply of long-chain fatty acids, such as those found in fish oil or healthy nuts, could be an effective way to improve not only general health but also the immune response to flu vaccinations improve,” says Kumar. In the long term, medication could also be used: “It would also be conceivable to reduce elevated levels of interleukin-15 before vaccination by administering suitable active substances in order to improve the immune response,” adds Li.
Source: Saumya Kumar (Center for Individualized Infection Medicine) et al., Science Advances, doi: 10.1126/sciadv.adq7006