Influenza activity remains high throughout the country, although it may be waning in certain regions, according to the CDC’s latest numbers.

In the week ending Jan. 5, geographically widespread flu activity was reported by 47 states, with regional activity in California and Mississippi and sporadic activity in Hawaii. The week before, widespread activity was reported by 41 states.

The proportion of outpatient visits attributed to flu-like illness was 4.3% in the most recent week, which is higher than the national baseline of 2.2% but lower than the rate seen in the last week of December (5.6%). The CDC noted, however, that the latter figure “may be attributed in part to a reduced number of routine healthcare visits during the end-of-year holidays, which has been observed in previous seasons.”

For the first time this season, the proportion of deaths attributed to pneumonia and influenza (7.3%) exceeded the epidemic threshold of 7.2%.

In an email, William Schaffner, MD, chair of the department of preventive medicine at Vanderbilt University in Nashville, classified the season as “moderately severe.”

“Some parts of the country have been affected worse than others (e.g., Boston, Philadelphia, and Chicago), but that is typical of flu and not entirely explained,” he said. “Recall that last year we had a record low year for flu, so perhaps we were a bit spoiled. This year is a reversion to a more conventional flu year, a touch on the severe side.”

Certain parts of the country may, in fact, be seeing declining flu activity at the same time others are seeing an increase in cases, the CDC numbers indicate.

In the week ending Dec. 29, 29 states and New York City reported high flu-like illness activity. The most recent numbers show just 24 states and New York City reporting that level of activity.

The net loss of five states from the high-activity total came as Arkansas, Florida, Indiana, Massachusetts, New York, Ohio, South Carolina, Vermont, and Wyoming reported a drop to moderate activity and four states — Delaware, Iowa, North Dakota, and West Virginia — reported an increase to high activity.

On a conference call with reporters, CDC director Thomas Frieden, MD, MPH, noted that flu activity can fluctuate during the season, so it remains to be seen whether declines will continue or activity will pick up again.

CDC data confirm that influenza A(H3N2) continues to be the predominant strain circulating this season. About 80% of viruses tested have been influenza A and nearly all of those subtyped have been H3N2, with very little H1N1. The rest have been influenza B viruses.

The H3N2 and H1N1 viruses examined have been nearly universally similar to their respective components in the seasonal influenza vaccine. About two-thirds of the B viruses match the vaccine strain.

In updating its numbers, the CDC also released preliminary data on the effectiveness of this year’s vaccine: 62%, indicating moderate effectiveness.

“What we’ve known for a long time is that the flu vaccine is far from perfect but it’s still by far the best tool we have to prevent the flu,” Frieden said, noting that the CDC is receiving reports of spot shortages of vaccine throughout the country and that most of the more than 130 million doses that were produced this year have been administered already.

Frieden also highlighted the effectiveness of antiviral treatment for patients who develop severe flu-like symptoms or for those who have underlying illnesses.

“Treatment with antivirals, especially in the first 48 hours after you become ill, can really help you avoid serious illness, hospitalization, or even death,” he said.

Like Schaffner, Gregory Poland, MD, director of the Mayo Vaccine Research Group in Rochester, Minn., also did not see anything particularly unusual with the spike in flu cases this year.

“I don’t see anything that is historically unprecedented here,” he said in an interview. “Rather, if you look across decades, not just a year or two or three, this is typical. We see waxing and waning epidemics, we see different virulence in terms of strains.”

That’s not to say that flu shouldn’t be taken seriously, Poland added, noting that the public health resources of some cities, like Boston, have been overwhelmed by the number of cases.

“To me, that’s a public health urgency,” he said, “and we really ought to be out there telling people it’s not too late to get vaccine, it’s important that you get vaccine, and the reason it’s important is because if you get infected, you’re going to miss school or work or run a chance of having a complication and being hospitalized, or in the worst cases, dying.”

Poland stressed the importance of everyone 6 months and older getting vaccinated each year — as recommended by the CDC — but placed particular emphasis on certain high-risk groups, including the very young, individuals who are older and more frail, those with chronic medical conditions, pregnant women, and the obese.

From: Medpage Today