Flu Season 2026-2027: What to Know About the Subclade K Flu Strain, the New mRNA Flu Vaccine and More

1. The flu changes every year.  

Dr. Roach: It’s important to get vaccinated every year because the flu itself changes  — so the protection that you had last year has largely worn off, and it was, to some extent, specific to last year’s flu.  

Experts can make educated predictions about which flu strains are most likely to circulate each flu season, and vaccines are formulated to target those expected strains. To do this, they look at flu activity in the southern hemisphere, particularly Australia and South America. While it's not always an exact match, their flu seasons often mirror what the Northern Hemisphere will experience months later.

Based on recent data from Australia, health experts are particularly concerned about a strain known as H3N2 subclade K. This year's flu vaccine was designed to provide protection against that strain.

2. Vaccination is the best defense for everyone, especially people in high-risk groups.

Dr. Roach: While anyone can get seriously ill from the flu, certain health conditions and characteristics put people at higher risk, including:  

• Chronic heart or lung disease (including heart failure, emphysema and severe arterial blockages)
• Smoking
• Immune system disease or suppression (including HIV, recent chemotherapy, or medications taken for autoimmune conditions)  
• Age 65 and older

Individuals over 65 are eligible for a special types of flu vaccines, since they are at higher risk of developing complications from the flu. One type, known as an enhanced vaccine, contains a higher dose than the regular flu shot. Another type, known as an adjuvanted vaccine, contains a substance that enhances the immune system's response to the flu.

That said, any flu shot is better than none at all. If you are over 65 but your doctor or pharmacist doesn't have these special vaccines available, go for the regular vaccine.

3. There’s a new type of flu shot this year that uses mRNA technology.

Dr. Roach: The FDA has recently approved a new type of flu shot for those over the age of 50 that uses the same type of mRNA technology that was used to create the COVID vaccine, expected to become available in the US for the 2026-2027 flu season.

In a head-to-head trial, the mRNA flu vaccine outperformed the standard flu vaccine in most measures. While it appears to offer better protection, it is also more likely to cause short-term side effects. People who receive the vaccine may be more likely to experience muscle aches, fatigue, low-grade fever or a general feeling of malaise, though these symptoms typically last less than 24 hours.

These side effects occur because mRNA vaccines are highly effective at priming your immune system to recognize and respond to viruses. As the immune system ramps up, some people may temporarily feel wiped out, low on energy, achy or develop a headache. While uncomfortable, these symptoms are generally a sign that the immune system is mounting a response.