H1N1 squelches seasonal flu in Minn.

In almost all ways it was a pretty typical January. There were sales, the usual thaw and the Vikings lost. But there was something missing -- the flu.

On Wednesday the Minnesota Department of Health reported that for the fourth week in a row there were no deaths from H1N1, and no hospitalizations for the second straight week.

Even more striking is the pandemic's silver lining -- it seems to have knocked out seasonal influenza altogether.

In a normal year seasonal flu would be peaking about now, but instead there are virtually no cases being reported in Minnesota or elsewhere.

"This was absolutely the quietest January influenza season we have seen in the last 40 years," said Michael Osterholm, an epidemiologist at the University of Minnesota.

The pandemic flu may or may not be over. The influenza virus in all its forms is highly unpredictable, and experts warn a third wave could appear between now and June -- or not.

"Flu is so fickle," said Dr. Greg Poland, an infectious disease expert at the Mayo Clinic in Rochester.

They also expect that next fall H1N1 will continue as the predominant flu strain around the globe, and they already are planning on that for the next vaccine. Each year the vaccine contains three of the flu strains that seem most likely to cause the seasonal outbreak.

Does that mean the H1N1 vaccine you already got will protect you next year as well?

Well, maybe, or maybe not. Experts say that between now and then the virus could mutate, and to prevent infection, everyone should get the new vaccine next fall.

Knockout was expected

H1N1's knockout blow to other strains of seasonal flu was not surprising, the experts say. In the two previous pandemics, in 1957 and 1968, the new flu strain that emerged somehow replaced the old ones in subsequent years. The 1957 virus was so stable that it was included unchanged in the annual vaccine for the next seven years. Following the 1968 pandemic, that vaccine was not changed for three years, and a form of that strain is still circulating now, Osterholm said.

It's still too soon to say whether the H1N1 outbreak is over for now, in part because there is still sporadic activity. Last week there were two school outbreaks reported to the health department -- one in the Twin Cities and one in southern Minnesota.

But state health officials are beginning to voice some optimism.

"I don't think we will get a very big third wave," said state epidemiologist Dr. Ruth Lynfield. If not, it may be because many in the population already are immune to the H1N1 virus, making the spread more difficult.

According to the Centers for Disease Control and Prevention (CDC), 55 million people in the United States have been infected with H1N1 and now are immune. In addition, one-third to half of people born before 1950 are believed to have some immunity because they were exposed to similar flu strains that circulated before that. On top of that, about a fourth of the population has been vaccinated.