This flu season is one of the worst in years on Long Island, with legions of people coughing, sneezing and aching -- and hospitalizations up more than 150 percent statewide compared with a year ago.
"I don't want to characterize it with a textbook definition," Eisenstein said Friday. "Flu is normal this time of year and what we are seeing certainly meets the definition of an outbreak."
Still, statewide statistics show an increase in hospitalizations and outbreaks in nursing homes.
In other parts of the country, a run on flu vaccines has created spot shortages, officials at the Centers for Disease Control and Prevention said during a news briefing Friday.
An estimated 130 million vaccine doses were manufactured for the 2012-13 flu season.
The vaccine supply remains robust on Long Island with no signs the region will run short, Eisenstein said.
"I know of doctors' offices that had a quick rush on it earlier this week," Eisenstein said, "but they were able to receive new supplies within 24 to 48 hours, so the shipping channels are certainly open."
This year's bout with influenza is a sharp contrast to the seasonal illness last year, when state health officials confirmed 4,400 flu cases statewide. This year more than 19,000 have been counted and the season has barely reached its midpoint.
Pediatric deaths, one of the leading measures CDC scientists use to determine the severity of any given flu season, tally 20 nationwide so far.
Two of those deaths occurred in New York, one in the central part of the state and the other in the metro New York/Long Island region, said Peter Constantakes, spokesman for the New York State Department of Health.
While 20 deaths are significant, they come nowhere near the 153 childhood deaths tabulated in the 2003-04 flu season, one of the worst on record.
CDC officials Friday attributed most of the wide-ranging outbreak to a major A strain of flu known technically as A/Victoria H3N2.
However, authorities in Boston, where a public health emergency has been declared, say both A and B strains are responsible for their outbreak.
Dr. Thomas Frieden, director of the CDC, described this year's vaccine, which protects against three strains of circulating flu viruses, as less than 100 percent effective -- but he still recommends vaccination.
"We've found the overall vaccine effectiveness to be about 62 percent," Frieden said, "which means you are 60 percent less likely to get the flu if you are vaccinated."
"We know the flu vaccine isn't perfect," he added, noting "young people are better protected than older people or those who have an underlying illness."
Dr. Pascal Imperato, dean of public health at SUNY Downstate Medical Center in Brooklyn, emphasized that a flu shot is still in the best interest of people 65 or older, even though they don't respond as well to the vaccine as younger people.
"Getting vaccinated can moderate the severity of the virus and that's also important in terms of population health," Imperato said. "The vaccine has a direct impact on the spread of the disease because it attenuates [lessens] the duration of the illness."