While many of us may be wishing for warmer weather, we are still in the throes of winter and with that comes cases of seasonal illnesses like RSV, the flu, and COVID-19. Flu (Influenza) cases in the U.S. have been rising more than usual with states across the country experiencing high or very high flu activity. It is estimated that there have already been 24 million cases of the flu, 310,000 hospitalizations, and 13,000 deaths from flu this season so far (since October 2024).
Getting the flu vaccine
Since the flu season often runs from October to May, it is still beneficial to get your annual flu vaccine if you have not already. It is recommended that everyone over the age of 6-months receive a flu vaccine. Flu activity is expected to continue increasing across the US in the coming weeks through the end of March or early April, so talk to a doctor or visit a health clinic as soon as possible if you are considering getting the flu vaccine this season.
Flu vaccines and the immune system
Flu vaccines contain harmless pieces of proteins from the influenza virus. These pieces of viral protein cannot cause disease but can trigger the immune system to help you develop immunity to the virus. When exposed to these pieces of influenza virus, the immune system learns to remember the virus and creates antibodies to combat the influenza virus during future encounters. Antibodies are protective proteins made by the immune system that target a specific pathogen, like influenza virus, and render them unable to infect cells in the body. In response to the flu vaccine, the immune system develops antibodies that target the hemagglutinin protein (HA) on the outside of the influenza virus.
However, the flu virus is ever changing. As the virus replicates, it can develop small changes in its genetics that can lead to changes in the proteins of the virus. These small changes cause parts of the virus, including HA, to change just enough that the immune system does not recognize it anymore. These constant small changes in influenza viruses are referred to as ‘antigenic drift’ and are why the flu vaccine is recommended annually.
Updating the Flu Vaccine
Each year, researchers change the flu vaccine to give your immune system an update on the best ways to fight influenza virus. The flu vaccine typically includes three different strains of the influenza virus. To choose which strains to include in the vaccine, professionals from the Food and Drug Administration, World Health Organization, and Centers for Disease Control and Prevention meet in the spring to review data on which flu strains are spreading across the globe and are most likely to cause disease that upcoming fall. Based on this data, they choose which strains of influenza are in circulation to include in the vaccine to offer the best protection in the upcoming fall and winter. Vaccine manufacturers then get to work producing the new flu vaccines with the selected strains so that they are ready by September before flu season begins.
Research and advancements
To address the need to both produce and administer new flu vaccines each year, some researchers are focused on developing a universal flu vaccine. A universal flu vaccine would be a vaccine that provides strong, long-term protection against multiple types of influenza virus. This kind of vaccine would mean a seasonal flu vaccine no longer needs to be updated and administered each year.
The hemagglutinin protein, one of the proteins the flu vaccine targets is made up of two parts: a head and a stem. While seasonal flu vaccines teach the body how to make antibodies to the HA head, the HA head changes often due to antigenic drift. However, researchers have identified that the HA stem rarely changes. Since antibodies work by remembering parts of the virus they have seen before, researchers believe using the HA stem to develop a universal flu vaccine would help the immune system to remember how to fight influenza virus season after season.
Recent research has also expanded to determine if mRNA vaccines could be used as flu vaccines. After the COVID-19 pandemic, researchers saw that mRNA vaccines could be much more easily updated compared to the traditional method of producing influenza vaccines to reflect changes in the virus. As a result, researchers are investigating mRNA vaccines for seasonal flu vaccines and their potential for a universal flu vaccine.
Immunology research is key to developing new and improved flu vaccines. Understanding how the immune system responds to influenza infection helps researchers describe what immunity (or protection) from the influenza virus looks like and measure the success of vaccines. If you’d like to learn more about the influenza vaccine and your options for the rest of flu season, talk to your doctor or local health clinic.