Challenge of flu vaccine lies in strains

Flu viruses are constantly mutating.

Which means that formulating the vaccine each year is always “a best-guess scenario,” said Paul Throne, of the Washington Department of Health.

So far this year, the dominant flu virus has been H3N2, and of the samples that have been tested, “about half of it has drifted slightly away from the vaccine formula,” said Throne, manager for health promotion and communications in the Office of Immunization and Child Profile.

“When the virus is reproducing, it basically creates little errors in its genetic structure, and over time those errors build up to the point where it no longer looks like it did before, and that’s considered a drift,” Throne said.

“The drift is sort of a minor mutation,” he said. What public health officials are more worried about is a shift.

“A shift is when it makes a dramatic, significant change and a new strain of flu can develop,” Throne said.

Fortunately, that doesn’t happen very often, he said. It did happen in 2009, when the H1N1 virus shifted, leading to the 21st century’s first influenza pandemic.

And though there’s been a drift this year, a flu shot is still the best defense against flu.

“The concern that I have is that people are exaggerating the vaccine’s inaccuracy,” Throne said, and using it as an excuse to not get a shot.

“Flu is a very, very serious illness,” he said.

It’s early in the flu season, which starts Oct. 1. Activity is still low in Washington and Idaho, though Spokane County has seen an earlier start to the season, said Mark Springer, an epidemiologist with the Spokane Regional Health District. As of Friday, 13 county residents had been hospitalized since September, including eight in November and two this month. Normally there’d be one or two hospitalizations at this point in the flu season, Springer said.

Idaho already has had three deaths from the flu this season, including one in North Idaho.

David Hylsky, an epidemiologist with the Panhandle Health District, said the person who died in North Idaho was an older adult with underlying health conditions.

With the drifted H3N2 strain, a lot of people won’t have antibodies that are able to recognize the virus, Hylsky said. And that means there could be more flu cases this year.

“We know it’s circulating in the community,” Hylsky said. “It’s definitely out there, so be prepared.”