Flu season is off to a slow start this year.

Influenza activity in the U.S. remained relatively low from October through January — so low, in fact, that the current flu season is considered not to have officially begun until the first week of February, when hospitals reported a slight increase, according to a report released today (Feb. 23) by the Centers for Disease Control and Prevention.

The last flu season that started so late was the one of 1987-88, the report said.

The majority of flu viruses now in circulation are similar to the ones in this year's flu vaccine, according to the CDC. "Efforts to vaccinate should be ongoing while activity is still low," the report said. It urged health care providers to offer the flu vaccine to all unvaccinated people 6 months and older throughout the influenza season.

Three children have died of influenza-related illness so far this flu season. Last year, 122 died during the entire flu season.

Since October, hospitalizations for flu have been highest among those younger than 4 (2.2 per 100,000 people) and older than 64 (3.2 per 100,000 people).

Flu cases have been reported in all 50 states, but just one of them, California, has reported widespread flu activity, meaning an increase in cases of influenza-like illness or hospital outbreaks in at least half the regions in the state.

So far, no resistance to the antiviral drugs oseltamivir and zanamivirhas been seen in the strains currently in circulation, the report said.

The report will be published tomorrow in the CDC's Morbidity and Mortality Weekly Report.

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