Swine flu lingers, making traditional flu season unpredictable

When people look back at 2009, swine flu will be remembered like an unwelcome house guest.

It arrived seven months early and stayed — for months.

It took a brief vacation in August, and then returned again just as school opened in the fall.

Although this second wave of the epidemic has tapered off from its peak weeks in October, the traditional time in Washington for influenza to hit hardest — January and February — is just around the corner.

The virus already is estimated to have killed nearly 4,000 children and adults nationally and sickened about 22 million people — many more than are sickened during an entire mild flu season.

That’s left parents, school teachers and even federal health officials asking: So what will this next “new” flu season bring?

“That’s like predicting what the snowfall is going to be on Mount Baker for the next three months,” said Dr. Yuan-Po Tu, medical director of walk-in clinics for The Everett Clinic.

The upcoming flu season could bring a third wave of swine flu, the onset of seasonal flu, or a mixture of both strains.

“That’s our concern,” said Dr. Anthony Marfin, an epidemiologist specializing in communicable diseases for the state Department of Health. “Unfortunately, people have to prepare for all three.”

Although the number of people coming to walk-in clinics with influenza-like symptoms and the percentage of patients testing positive in initial or rapid tests for flu has declined over the past month, it doesn’t mean people should let down their guard, Tu said.

“Don’t get sucker-punched,” he said. “It’s very, very early in the flu season, and we have a long way to go.”

Hospitalizations and deaths from influenza tend to continue, even when the number of new infections are declining.

In the past month, five people have died in Snohomish County from swine flu or its complications, including a 5-month-old from Tulalip.

Late last week, Providence Regional Medical Center Everett had six patients in its critical care unit with suspected or confirmed cases of swine flu.

“The message we’re trying to drive is … even though the number of new cases we’re seeing has gone down in the last four weeks or so, it’s still out there,” Tu said. “You have to have a lot of respect for this virus.”

Vaccination still key

Based on past outbreaks, influenza pandemics typically affect about 30 percent of the population in the first 12 months, he said. So far, roughly 8 percent of the population in the United States has been infected.

Some countries in the southern hemisphere, which have already turned the page on their winter flu season, report that about 75 percent of influenza cases were swine flu and 25 percent seasonal flu, Tu said.

In the United States, nearly all cases of influenza to date have been swine flu, although a tiny number of cases of seasonal flu have been reported.

“As far as whether the seasonal flu virus will come around, we just don’t know,” Tu said.

Any temporary lull in swine flu will allow vaccine production to begin to catch up with demand, a chance he said he hopes the public takes advantage of.

The reason swine flu spread so quickly this year is no one had immunity. It was a new flu virus, a cocktail with influenza bugs from pigs, birds and humans.

If all 200 million doses of the swine flu vaccine expected to be produced in the United States are administered to children and adults, “that would potentially prevent a big outbreak in the spring,” he said.

While some parents continue to have concerns about the vaccine, on Friday, Dr. Thomas Frieden, director of the national Centers for Disease Control and Prevention, said that so far, the news on the vaccine’s safety is “very reassuring.”

The peak of infections from the second wave of swine flu, which began in late August in Washington, has now passed, Marfin said.

That jibes with the general pattern of flu outbreaks, which typically last 10 to 12 weeks in any geographic region, he said.

“The question is: Why does it end after 10 to 12 weeks? We don’t think most people are now immune, so why does this wave stop?”

He and other health officials worry that people will put too much stock in what is probably a temporary decline in infections, using it as an excuse to not be vaccinated.

“January and February are our traditional months of influenza transmission,” Marfin said. “If you have enough susceptible people, we have a deep concern we can rekindle another outbreak. The only way we can stop that is by getting people vaccinated.”

Ups and downs common

Concern that swine flu can mount a third-wave attack is based on the study of previous epidemics, such as the Spanish flu pandemic, which first appeared in 1918 and returned in 1919.

“If we look over influenza seasons in the past, there can be multiple ups and downs,” said Dr. Anne Schuchat, director of the national center for immunization and respiratory diseases at the CDC.

“We may have weeks and months of a lot of disease ahead of us,” she said.

Some 1.4 million doses of vaccine have been distributed in Washington, enough to immunize about 23 percent of the state’s population. The initial goal was to get about a quarter of the population immunized, Marfin said.

Perhaps by the middle of this month, there will be enough vaccine to administer it beyond those groups for which it initially has been reserved. That includes pregnant women and people between 6 months and 24 years old because they have the highest risk of severe complications if they get swine flu.

This virus, unlike typical seasonal flu, has hit younger people the hardest.

Many others have been excluded from getting the immunization. This includes seniors and healthy people 25 and older who don’t have diseases such as asthma or diabetes. People with underlying health problems have a greater risk of dying when swine flu attacks them.

If swine flu returns, its severity in large part depends on how many people are vaccinated, Marfin said.

Scientists were prepared

Since the beginning of the swine flu, or H1N1 outbreak, this spring, many of the details on how the virus was spreading in Washington state — and just how deadly it was — were pieced together by scientific detective work at the state Department of Health’s lab in Shoreline.

For workers at the lab, the outbreak of a flu pandemic was like a viral D-Day, something for which they had long trained.

Public health officials across the nation generally assumed that they would be battling avian or bird flu, not a new virus made up of genes from birds, people and pigs.

It’s hard to remember now just how much they and other public health officials didn’t know about this never-before-seen mix of viruses when the outbreak first began. They worried it could be far more lethal than the more typical strains of seasonal flu.

So at the beginning of the outbreak, samples from every suspected swine flu patient were sent to the lab. At the time, it was the only lab in the state that could do the work, triggering a tidal wave of tests.

In a typical year, the lab tests 130 samples for flu between January and October, when scattered cases of influenza begin to be reported.

This year, from the onset of the first reported cases in the spring until mid-November, it tested 3,514 samples — and more than 2,000 of those were tested in the two-month period from the end of April until the end of June.

Now, only the most serious cases — samples from people who are hospitalized or are suspected to have died from swine flu — are sent to the lab for analysis.

Nearly all suspected influenza samples sent to the lab so far have been labeled as swine flu, with the positive identification coming from the virus’ unique genetic fingerprint.

Yet scientists are vigilantly looking for clues to determine whether seasonal flu is beginning to circulate. They’re also looking for changes in the swine flu virus that could signal it’s becoming more virulent or deadly.

The work at the lab is part of a national effort to monitor for changes or mutations in the swine flu virus, said Troy Leader, a molecular epidemiologist.

So far, the swine flu virus has remained stable, he said.

“With any virus you would expect small changes that would occur,” he said. Many mutations do not alter the illness the virus causes.

They’re also checking to see if the virus is changing to become more resistant to Tamiflu, an antiviral medication that helps reduce the illness’ severity.

“That’s exactly why we’re concerned about it,” Marfin said. “If resistance is up, we don’t have the medicine to treat the most severe cases.”

There have been scattered reported cases already of people with antiviral-resistant swine flu, including two chemotherapy patients in Washington.

There also have been reports in Europe of resistant strains of swine flu being transmitted among hospital patients, said Yolanda Houze, the lab’s director of microbiology.

“Influenza viruses are always changing, always mutating,” Marfin said. “Sometimes it really is a survival-of-the-fittest story — they can out-compete other viruses and become the dominant virus.”

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Swine flu’s toll

In Snohomish County, two men died of swine flu in the spring, and five more people, four adults and a 5-month-old boy, have died in recent weeks. Since mid-September, 92 people in Snohomish County have been hospitalized for influenza symptoms. In Washington, 1,274 people have been hospitalized for flu since Sept. 19 and 62 have died.

Estimated number of swine flu cases this year in the U.S.:

Children 17 and under

Ill: 8 million

Hospitalized: 36,000

Died: 540

Adults 18 to 64:

Ill: 12 million

Hospitalized: 53,000

Died: 2,900

Adults 65 and over:

Ill: 2 million

Hospitalized: 9,000