New evidence suggests that people in their 60s might be somewhat protected against the spreading swine flu because they may have been exposed earlier to a similar strain, government health officials said.
Test results released Thursday of blood samples from 350 people showed that a third of adults older than 60 had developed antibodies that might confer some protection against the novel H1N1 virus, said Dr. Anne Schuchat, a public health official with the federal Centers for Disease Control and Prevention.
But Schuchat cautioned that the results were in laboratory tests, not humans; that they involved a strain that's a distant relation of the current virus; and that it's not clear how much, if any, protection older people actually would have. They're encouraged to take the same precautions against the new flu as their children and grandchildren.
“The important feature is that we saw a difference in pre-existing antibody levels in seniors," Schuchat said. “Whether it will pan out over time that seniors don’t get this infection, we can’t say.”
But the results from tests of stored blood from people ages 6 months to older than 60 who were later vaccinated against seasonal flu are a clue about the pattern of the current outbreak, she added.
The results could help explain why most of the cases of swine flu infection in U.S. appear to be targeting children and young adults, and why hospitalizations and complications are most common among younger people as well.
Only about 1 percent of the more than 5,700 cases of swine flu in the U.S. are in people older than 65, Schuchat said.
So far, the flu has affected more than 5,764 people in the U.S., with more than 250 hospitalized and at least 10 deaths. Worldwide, there are more than 11,000 cases and 85 deaths.
Older people might have been exposed to variations of the the H1N1 flu strain that first emerged in the 1918 pandemic and then continued to change and to circulate around the globe. That could have provided some, but not total, protection against the strain that has emerged this year, the laboratory tests suggest.
In 1957, a new flu subtype, H2N2, emerged, eclipsing the previous virus and becoming the dominant strain, CDC officials.
The new information, gathered through cooperation of several government health agencies, also indicated that seasonal vaccine has "little or no immune benefit" against the novel flu, Schuchat said.
On Wednesday, Utah officials reported the state's first death associated with swine flu and Arizona recorded that state's third victim, pushing the national death toll to 10 people.
David Sundwall, executive director of the Utah Department of Health, said a 21-year-old man with swine flu died Wednesday morning at a Salt Lake City hospital.
Sundwall said the man was overweight and had chronic medical conditions, including respiratory problems and other health issues, that would put him at risk.
Dagmar Vitek, medical director for the Salt Lake Valley Health Department, says an investigation to determine how the man contracted the virus is under way. She said officials don't believe he traveled recently.
In neighboring Arizona, health officials said Wednesday a 13-year-old boy from Tucson also has died with swine flu. The teenager died Friday of complications from the flu. He had been hospitalized May 10.
The Arizona Department of Health Services, which confirmed test results, said an older sibling of the teen is hospitalized with the virus, and other family members have recovered from the flu, according to spokeswoman Patti Woodcock.
Worldwide, more than 10,000 people in 41 countries have been affected, including 83 deaths.
The number of suspected and confirmed cases likely represents only a fraction of the actual cases of swine flu in the community, Jernigan said.
The virus appears to infect people at about the same rate as the seasonal flu, Jernigan said. Most cases remain mild, although there is the possibility of severe complications, including death, in people with underlying conditions such as pregnancy, asthma or heart disease.