Flu season is on the rise, and a more severe strain dominates: What you need to know

Since the start of 2019, influenza has been steadily on the rise in the U.S., with the number of new cases currently above the national baseline. And while this flu season has not been quite as severe as seasons past, there has been a recent uptick in a less common flu strain, the H3N2 virus, now accounting for over 50 percent of new cases, according to recent data from the CDC.

The H3N2 strain: More severe

There are two main groups of influenza viruses: influenza A and influenza B. The H3N2 strain belongs to the influenza A family.

“The H3N2 strain does appear to be more severe,” says Dr. Olaoluwa Fayanju, senior medical director of Oak Street Health in Cleveland, Ohio. “In addition to the typical symptoms of flu, which include fevers, chills, body aches, and rigors [shaking chills], it additionally has the potential of causing several severe complications, including very high fevers up to 103 or 104 degrees Fahrenheit.”

Dr. Fayanju also notes that people over 65 are at particularly high risk for complications. “The vulnerability caused by a flu infection allows other systemic diseases to take hold,” he says. These include diabetes, stroke, pneumonia, heart attacks, chronic obstructive pulmonary disease (COPD) and sepsis.

Populations at risk

Everyone is at risk, especially those who have not yet been vaccinated. However, as with the more common H1N1 virus, the elderly and very young children are at increased risk of developing complications. According to Dr. Fayanju, this is because young children have not been in the world long enough to develop the antibodies, or any kind of immunity to these viruses. People with chronic diseases, included diabetes, COPD and heart disease are also at increased risk of developing complications if they become infected.

What you can do to prevent infection

“Number one: get vaccinated,” says Dr. Fayanju. Even if you have not yet been vaccinated this season, it is not too late. Dr. Fayanju emphasizes how important it is, especially with the uptick in this new, more severe strain. “The flu vaccine includes an amalgam of subtypes and variants of influenza A and B, and is developed by scientists worldwide,” said Dr. Fayanju. In previous years, the flu vaccine has been less effective against the H3N2 strain, according to the CDC. However, the flu vaccination this season appears to demonstrate similar effectiveness on H3N2 as it does with other strains.

Dr. Fayanju also recommends other actions to prevent getting sick:

1. Wash your hands frequently with soap or hand sanitizer. “This is very important. I joke with my daughters to hum the happy birthday song for 30 seconds,” which is how long you need to thoroughly wash your hands of any pathogens. This is especially important after you touch surfaces that could be contaminated with flu, such as after taking public transportation. Avoid touching your mouth, eyes, or nose before you wash your hands.

2. Get lots of sleep, at least 6-8 hours per night

3. Stay hydrated

4. Stay active: exercise is a great way to stay healthy

5. Eat healthy foods

Predictions for the rest of the season

Each week, the CDC comes out with weekly flu statistics from across the country. Many experts think we may be hitting the peak of flu cases now, according to Dr. Fayanju, but with the recent increase in cases of H3N2, it is more difficult to determine how long the season will last. Therefore, it is important to get vaccinated if you have not already, to keep an eye out if you develop any symptoms of the flu, and to contact your doctor if you do.

Ashley Knight-Greenfield, MD, is a diagnostic radiology resident and member of the ABC News Medical Unit.