No Seasonal flu this year?

[Guest guest]

Swine Flu Means Killer Winter Influenza May Not Come (Update1)

By Tom Randall

Dec. 17 (Bloomberg) -- Seasonal flu, which annually kills 30,000 Americans 65

and over, may not appear in the U.S. for the first time in more than 40 years,

crowded out by the swine flu pandemic and mass vaccination campaigns.

Seasonal strains are almost nonexistent in reports from countries where swine

flu, or H1N1, has taken hold. In the U.S. and Europe, 99 percent of influenza

cases tested last week were H1N1, according to government reports. Seasonal

versions of virus that usually arrive in December and peak in February may not

emerge at all, said Marc Lipsitch, a flu tracker at the Harvard School of Public

Health, in Boston.

" I would bet against a seasonal flu this year, " said Lipsitch, a professor of

epidemiology, in a telephone interview. " But I wouldn't bet very much money. "

One of the seasonal strains most likely to appear this year, known as type B,

was responsible for 7 of 478 positive cases in a testing sample for the week

ended Dec. 5, according to the U.S. Centers for Disease Control and Prevention.

A second form, H3N2, hasn't been spotted at all.

Neither seasonal strain emerged after H1N1 struck in the Southern Hemisphere,

where the winter flu season ended in September, according to the World Health

Organization in Geneva.

Infections Decline

Swine flu infection rates decreased in each of the last six weeks, the

Atlanta-based CDC reported. That has spurred a debate among health officials on

whether the H1N1 pandemic is grinding to a halt, and whether that strain will be

replaced by a surge of seasonal cases as the Northern Hemisphere enters winter.

H1N1 infected 50 million people in the U.S. and killed an estimated 10,000

through Nov. 14 from the start of the pandemic in April, the CDC reported last

week. About 90 percent of swine flu deaths were among people younger than 65.

With seasonal flu, the effects are reversed, with more than 90 percent of annual

deaths among those ages 65 or older, according to the CDC.

Influenza is notoriously difficult to predict, said Frieden, the CDC

director, in a conference call today. A dozen scientists surveyed by the CDC

were split on the likelihood of a wave of new cases of either type of flu in

January, when children return to school from winter recess.

Researchers Divided

Eight flu researchers surveyed by Bloomberg were similarly divided, though most

agreed this year's worst flu days are over. With each week that goes by without

seasonal flu, the possibility of widespread outbreaks diminishes, said Arnold

Monto, professor of epidemiology at University of Michigan, in Ann Arbor.

" Two months ago, I would have said we're going to see the seasonal viruses, "

said Monto, who is also a member of the WHO's emergency advisory committee. " But

we haven't seen anything yet, and we normally would have seen activity by now. "

Scientists aren't sure exactly how some flu strains can crowd out others, said

Schaffner, chairman of the department of preventive medicine at

Vanderbilt University in Nashville, Tennessee, and an outside adviser to the CDC

on vaccine policy.

One theory involves the receptors where flu viruses attach themselves to lung

cells. When a person catches the flu, the virus infects almost all of the

exposed lung cells and occupies those receptors, Schaffner said in a Dec. 11

telephone interview. When a different virus comes along, it has nothing to

attach to and is " crowded out, " he said.

Protective Defenses

When a pandemic strikes, and a new strain whips through a population with little

natural immunity, so many people get sick simultaneously that a seasonal flu

strain can't find enough hosts with vacant receptors to spread, Schaffner said.

The immune system also produces interferons, proteins that trigger protective

defenses in response to an initial infection that can last for days after the

first virus has cleared out.

Crowding out occurred in the Southern Hemisphere, where swine flu struck at the

same time that seasonal strains would normally be active, Schaffner said. In New

Zealand, Australia, Chile and Argentina, once the pandemic took root, seasonal

flu cases were almost nonexistent.

In Northern Hemisphere countries including the U.S. and U.K., swine flu struck

months before the normal start of flu season. By January, most patients will

have recovered, and their lungs may be ready for another bout of flu, Schaffner

said in a telephone interview. Swine flu may be nearing its end and seasonal flu

just beginning, he said.

`Crowding Out'

" I'm not so sure how strong the crowding-out theory is, " Schaffner said. " It

certainly seemed to play a role in the Southern Hemisphere, but we anticipate

there will not be crowding out in January and February. "

A wall of resistance against swine flu is expanding as people recover from the

illness with newly acquired immunity, and as the country's biggest-ever flu

vaccination program expands to reach more people, said Ira Longini, of the

University of Washington in Seattle.

About 100 million doses of swine flu vaccine will be available in the U.S. by

the end of this week, and most states have enough doses to give the vaccine to

anyone who wants one, U.S. health officials said today.

Minnetonka, Minnesota-based UnitedHealth Group Inc., the top U.S. insurer by

revenue, isn't budgeting for additional costs to treat H1N1 next year, Chief

Financial Officer Mike Mikan said Dec. 1 at an investor conference in New York.

Sharp Peak

Flu viruses circulate in waves of infection with a sharp peak followed by

declining rates. The first wave of swine flu cases came after the virus emerged

in April, according to CDC data. The second and larger peak started when pupils

returned to schools in September and peaked in late October.

" My intuition tells me if we're going to have a third peak it would have to be

under conditions in which the virus spreads to older populations, " said Longini,

a biostatician who advises the U.S. government on flu, said in a Nov. 24

interview.

" You'd expect a combination of natural immunity and now vaccination would more

or less eliminate the possibility of a big third wave in children, " Longini

said.

Based on past pandemics and on what happened in the Southern Hemisphere,

seasonal flu is also unlikely this year, Longini said.

Fear of pandemic swine flu heightened public vigilance in the U.S. against

seasonal influenza, causing an early rush for vaccinations beginning in

September, and spot shortages around the country, according to the CDC. The U.S.

supply of seasonal flu vaccine is " coming to the end, " the CDC's Frieden said.

Seasonal Flu

" There's no way to know for sure what will happen with seasonal flu this year.

We're seeing very little of it so far, " Frieden told reporters today at the

National Press Club in Washington. " We have had the same amount of seasonal

vaccine this year as in prior years; we've had a lot more interest in getting

vaccinated. "

The CDC doesn't immediately track the number of people who are vaccinated for

seasonal flu. A survey by Rand Corp., a nonprofit research group based in Santa

, California, found about a third of U.S. adults were vaccinated by mid-

November, a rate similar to last year. About 17 percent said they still intend

to get vaccinated.

Vaccine suppliers Sanofi-Aventis SA of Paris, London-based AstraZeneca Plc and

GlaxoKline Plc, Basel, Switzerland- based Novartis AG, and CSL Ltd. of

Australia are making 114 million seasonal-flu doses and 251 million swine flu

doses for the U.S., according to the U.S. Health and Human Services Department.

Next Season

" The conventional wisdom among our flu epidemiologists is that pandemic H1N1

will dominate at least through the next flu season 2010-2011, but no one really

knows, " said Mercer, acting head of the communicable diseases unit of the

WHO's European region, in an e-mail today. " We are recommending both pandemic

and seasonal flu shots. "

The University of Michigan's Monto said he thinks there will be more swine flu

cases in January, with outbreaks primarily in areas the disease has so far

skipped. The number of flu-related deaths this winter is likely to be smaller

than normal, Monto and Harvard's Lipsitch said.

Since swine flu attacks children and young adults instead of the elderly, more

years of life will be lost this year, and that is the true toll of a pandemic,

said Lone Simonsen, research director in the department of global health at

Washington University, in Washington.

The " hallmark " of any new pandemic strain is that it targets young people, and

that pattern is likely to continue with swine flu for two to five years,

Simonsen said.

1968 Pandemic

The last time seasonal flu strains were crowded out entirely in the U.S. was

during the Hong Kong flu pandemic of 1968, Simonsen said. She predicted that

swine flu will return in January and may circulate simultaneously with seasonal

flu strains, potentially attacking the young and old.

" It's probably still a very good idea to get vaccinated, because this is not

over, " Simonsen said in an interview on Dec. 8. " I don't have a crystal ball,

but we had two historical pandemics where there was an early fall wave -- 1918

and 1957 -- and both of those were followed by a winter wave. "

Last Updated: December 17, 2009 12:22 EST

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