Flu vaccine can't handle mutated influenza strain

Hamilton is seeing at least a slight increase in the number of flu cases thanks to a strain of influenza that isn’t covered by this year’s flu shot.

The vaccine administered this fall only offers minimal coverage against a specific type of H3N2 influenza strain, said Dr. Ninh Tran, the city’s associate medical officer of health. That means even people who had a flu shot are getting sick with influenza A. The U.S. Center for Disease Control has also issued a warning that the influenza strain has mutated. 

The issue is rearing its head the most during the holiday season, when people get together with family and friends, Tran said. Hamilton Public Health issued a warning to hospitals and clinics earlier this month that the vaccine didn’t match the mutated version of the specific H3N2 strain, and they should expect greater crowds.

Since September, health care providers have reported 77 cases of the flu in Hamilton, 75 of which are influenza A. The bulk of those are likely the H3N2 strain, Tran said.

“I would say that’s probably reasonably high for this time,” he said “We are at least seeing a bit of an earlier peak than some other years.”

This year’s vaccine contained three strains. Two were specific to influenza A and one covered influenza B.

The influenza A strain in question is included in the vaccine, but “it’s not the best match for the specific strain out there," he said. “That’s why we’re seeing cases of influenza A in our community and nationally.”

So “we are going to probably see more case of influenza A, despite our best efforts.”

Emergency rooms at Hamilton Health Sciences are seeing an increased number of patients with flu-like symptoms, said Dr. Paul Miller, an ER physician.

Patients can avoid the virus by washing hands and using an alcohol-based hand sanitizer, Miller said.

If people do have symptoms, they should stay away from others who are particularly susceptible, such as the elderly and people with complex medical conditions.