Influenza A and B: What's the Difference?

Patients have been steadily arriving in significant numbers to the McLaren Oakland and McLaren Clarkston emergency departments with symptoms consistent with influenza B, signaling a spread of the flu strain within the community.

This late-season spike comes on the heels of a weaker flu season, when compared to previous years.

"Having fewer cases of influenza A does not have any impact on the prevalence strains of influenza B can have," said Dr. Harrison Tong, physician and director of emergency medicine at McLaren Oakland and McLaren Clarkston. "One does not increase or decrease the spread of the other, but it's quite common to see late-season surges like we're currently seeing."

Dr. Harrison Tong
Emergency Medicine

While the symptoms of influenza B mirrors those of A, the main difference between the two strains is who it can affect. Strains of influenza B are exclusively contracted by humans, while A can be carried (and spread) by animals, however, both strains are transmitted mainly by respiratory droplets from coughing and contact with an infected person.

This allows strains of A to be spread more rapidly than B, while also meaning strains of B cannot cause pandemics with symptoms likely less severe. Flu shots protect against both strains of influenza.

"There are some differences from influenza strains A and B, but this does not diminish the need for medical intervention," Dr. Tong said. "If you or someone you know starts to show symptoms, avoid contact and seek treatment, especially those patients with high fever, extremes of age and those with a compromised immune system."