The flu season is off to an early and deadly start in Wisconsin, with 26 hospitalizations and four flu-related deaths reported here already, according to the state Division of Public Health.

Public health officials aren’t sure what’s behind the uptick in hospitalizations so early in the season.

A previously seen influenza A H3N2 strain - the dominant strain so far this flu season - appeared to be a good match for the current vaccine, said Paul Biedrzycki, director of disease control and environmental health for the Milwaukee Health Department.

“However, you can’t rule out a possible mutation in the flu virus,” Biedrzycki said Monday. “Flu viruses change unexpectedly and arbitrarily.”

During the last two to three flu seasons, no flu-related hospitalizations were reported before January, said Tom Haupt, the epidemiologist at the Wisconsin Division of Public Health in charge of influenza surveillance.

On Monday alone, 14 hospitalizations were reported to the state, including four pregnant women who did not get flu shots, Haupt said. Statewide, between Oct. 5 and Friday, 113 laboratory-confirmed influenza cases had been reported, compared with seven cases at this time last year.

Haupt urged other pregnant women to get the flu vaccine, which takes about two weeks to provide full protection.

This is the earliest flu season in nearly a decade, since the winter of 2003-‘04, which turned out to be one of the most lethal in about 35 years, the federal Centers for Disease Control and Prevention reported Monday.

During the 2003-‘04 flu season, more than 48,000 people died nationwide. The dominant flu then is the same dominant strain seen so far this season - A/H3N2 (the same subtype as Hong Kong flu) - according to the CDC. This influenza strain generally causes more severe flu seasons. It’s related to the Hong Kong pandemic strain, which caused nearly 34,000 deaths in the United States in 1968 and 1969. That was the last pandemic before the 2009 swine flu pandemic (also known as H1N1).

Scientists are now investigating whether the genes of the seasonal A/H3N2 could have mutated, resulting in a more severe and/or more easily transmissible flu not covered exactly by the flu vaccine developed six to eight months ago, Biedrzycki said.

“It has to be a change in the bug or a change in susceptibility, which could include low vaccination rates,” he said.

With the flu season starting earlier this year, it also may peak earlier - around the holidays, public health officials said.

Local and federal public health officials still stress that a flu shot provides the best protection.

“If there was a change in the virus, there may be some cross-protection from the current vaccine and it may prevent increased transmission to very vulnerable populations” - the young, pregnant women and elderly, Biedrzycki said.

Haupt said no vaccine is 100% effective.

“Its primary design is to prevent complications - hospitalizations and death” - especially among the elderly and very young, who have weaker immune systems that can’t build full immunity, he said.

Of the first 12 influenza-related hospitalizations this season in Wisconsin, three-fourths had not received flu shots, Haupt said. Four of the 12 were ages 18 to 49, two were ages 50 to 64, and six were 65 or older.

Those who did get the shot but developed flu complications anyway did not gain full protection from the flu shot. Information on the 14 others hospitalized was not immediately available.

More people than the reported 26 probably have been hospitalized with complications of influenza in Wisconsin, Biedrzycki said.

Reporting isn’t always as good as it should be, he said.

Biedrzycki said the Milwaukee Health Department will step up influenza surveillance, closely examining medical examiner’s reports from death investigations and reminding hospitals that state law requires them to report acute respiratory illnesses.

Accurate reporting of influenza helps public health officials better monitor its spread and severity, he said.

Long-term care facilities are required to report influenza or respiratory illness outbreaks - three or more cases, diagnosed or not. So far this flu season, two outbreaks have been reported at long-term care facilities in Wisconsin, and two people died in each outbreak, Haupt said.

The CDC recommends everyone older than 6 months old get vaccinated against the flu.

As of Monday, about 37% of those 6 months and older had received a flu shot, according to the CDC.

Last year, nearly half (48%) of the population was vaccinated against the flu by the end of the influenza season.

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How to avoid the flu

Don’t put off getting a flu shot. It’s not too late to get vaccinated, especially given the approach of the holiday season, when families and friends may spread the virus during holiday gatherings.

It takes about two weeks to develop full immunity, and there’s plenty of vaccine available. Get a shot while you holiday shop at Target, Wal-Mart and other convenient venues in the community.

Flu shots are not just for grandma and grandpa. Everyone older than 6 months (who is medically eligible) should get vaccinated. FluMist (intranasal) also is available for healthy individuals ages 5 to 49.

Flu does hospitalize and kill people. It’s difficult to predict the severity given mutations that can occur early to midseason, well after a vaccine has been developed.

Potential for co-infections of the most vulnerable may be of concern this year. Pertussis (whooping cough), norovirus (a gastrointestinal virus) and rhinovirus (a respiratory virus) also are circulating in the state and region.

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By Karen Herzog of the Journal Sentinel