U.S. Says Older People Appear Safer From Virus

By DONALD G. McNEIL Jr.
Published: May 20, 2009
Confirming the first impressions of many American and Mexican doctors, federal health officials said on Wednesday that people born before 1957 appear to have some immunity to the swine flu virus now circulating.
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Times Topics: Swine Flu (AH1N1 Virus)
Tests on blood serum from older people showed that they had antibodies that attacked the new virus, Dr. Daniel Jernigan, chief flu epidemiologist at the Centers for Disease Control and Prevention, said in a telephone news conference.
That does not mean that everyone over 52 is immune, since some Americans and Mexicans older than that have died of the new flu. But it bears out what doctors in the field have noticed: that the new flu infects and hospitalizes many more young people than seasonal flus, which tend to sicken and kill the very old.
Only 13 percent of the 247 people hospitalized because of the new flu are over 50 years old, Dr. Jernigan said. Many have other medical conditions like pregnancy, asthma, heart disease, lung disease or obesity. In a typical flu season, more than 90 percent of those hospitalized are older than 50.
There have been eight deaths in the United States from the new flu, the latest a woman in Arizona.
The World Health Organization has confirmed cases in 41 countries.
In the United States, 78 percent of the influenza samples subtyped since the last weekly report are the new swine flu, meaning that it is persisting as the seasonal flu is disappearing.
The protection theory, Dr. Jernigan explained, is that from 1918 to 1957, all circulating seasonal type-A flus were weakened descendants of the 1918 Spanish flu, which was an H1N1, as the current swine is. (All flus are named for the shapes of hemagglutinin and neuraminidase displayed on the virus’s shell. Hemagglutinin is sometimes called the “spike”: the virus uses to enter a cell, while neuraminidase is the “helicopter blade” that chops off receptors, allowing newly made virus to escape.)
Then in 1957, an H2N2, the Asian flu, emerged and displaced it. It was replaced in 1968 by the H3N2, called Hong Kong flu, which has persisted as a seasonal strain.
A different and milder H1N1 emerged in 1977. It was isolated in China but is called the Russian flu because of a suspicion it escaped from a Soviet laboratory. That H1N1, the 1968 H3N2 and a B strain have all circulated in humans ever since, and the seasonal flu shot is aimed at them.
Neither those shots nor the 40 million flu shots dispensed during the 1976 swine-flu scare are known to provide any protection against the new swine flu.
Dr. Jernigan said the Centers for Disease Control would probably urge vaccine manufacturers to “have an earlier rollout of seasonal vaccine this year.”
Flu shots are usually shipped in October, but the agency hopes to make room in storage facilities and encourage people to get the seasonal shot and then later the new swine flu shot that is being worked on.
Rapid progress is being made on a new seed strain for that shot, and it may be shipped to vaccine makers by the end of May, he said. After that it should take at least four to six months to produce the first batches, the World Health Organization has said.
Dr. Jernigan also said that relatively few health care workers had become seriously ill thus far in the current outbreak, but that some of those who did had been infected not by patients but by work colleagues.
“Folks who are sick should stay home,” he said, adding that hospitals and nursing homes are supposed to make sick employees do so. “We’re seeing some problems with administrative controls.”