Flu 'super' variant spreads: 30 states are in CDC's worst tier

(NEXSTAR) – New data released by the Centers for Disease Control and Prevention on Monday shows a massive spike in flu activity nationwide.

In just one week, between Dec. 20 and Dec. 27, the country saw a 33% increase in people testing positive for influenza. There was also an 8% increase in people visiting a health care provider with flu symptoms.

The updated data, whose release was delayed by the New Year holiday, now includes the week of Christmas – a time when people travel and gather and respiratory illness tends to spread.

In mid-December, before the peak holiday season, only six states were considered to have “very high” flu activity. As of Dec. 27, 30 states from New England to the South and the Midwest have moved into that highest tier. (See the full list of states considered “very high” at the bottom of this story.)

Only a small handful of states are still considered to have “low” or “moderate” flu levels: Montana, South Dakota, Vermont and West Virginia.

Compare the change in flu activity between Dec. 13 and Dec. 27, just two weeks later, by sliding between the images below. Note: Nevada reported insufficient data for the week ending in Dec. 27 but was in the “high” category the week prior.

(The Centers for Disease Control and Prevention)

We likely haven’t reached the peak yet. Influenza activity “continues to increase across the country,” the CDC said Monday.

The rapid rise is largely being driven by a new variant of the flu virus known as “subclade K.” This subtype of influenza A led to outbreaks in Canada, Japan and the United Kingdom, where flu season starts earlier than here in the U.S.

In the United Kingdom, NHS National Medical Director Meghana Pandit said the “unprecedented wave of super flu” was straining the country’s health care system.

Experts fear low vaccination rates in the U.S. could lead to a historically bad flu season, but they say there’s still time to course-correct.

“It is not too late to get a flu shot,” said Dr. Andrew Pekosz, a virologist and professor at Johns Hopkins Bloomberg School of Public Health, said during a media briefing in December. “We’re really at the beginning of the influenza season here in the U.S.”

Since the early 1980s, the most commonly observed peak of flu season has come in February, but cases often ramp up starting in December.

The states with “very high” flu activity, according to the CDC, are: