# 448
This isn't exactly a new idea.
After all, we've always assumed the attack rate during a pandemic would be on the order of 30% - 40%, even with a novel virus. Some people would likely be immune. At least that was the experience in the 1918 Spanish Flu, where just under 30% of the country fell ill.
Today's announcement may give us some clues as to why this might be. Previous exposures to other influenza viruses may confer partial immunity, even if the viruses aren't closely matched. The operative words here being `partial' and `may'.
It stands to reason that the older a person is, the more influenza viruses they will have been exposed to, and so their level of immunity is apt to be higher. This might explain why so many H5N1 infections have been seen in younger patients.
While this is important research, and may help to explain why some people may be immune to a novel virus, it probably doesn't change much regarding a pandemic. It may mean that older persons will be at less risk, but we simply don't know that yet.
Study suggests possible bird flu immunity
By Maggie Fox 20 minutes ago
WASHINGTON (Reuters) - Could some people have a little immunity to the H5N1 bird flu virus? An animal study published on Monday suggests it is theoretically possible.
The researchers found that mice inoculated with a human virus known as H1N1 were less likely to die when they were infected with a little bit of H5N1 -- although this protection went away after a bigger dose of H5N1.
The finding suggests it is possible that some people previously infected with or vaccinated against flu may have a slight protection from H5N1, the researchers wrote in the Public Library of Science journal PLoS Medicine.
"It is weak protection," said Richard Webby at St. Jude Children's Research Hospital in Memphis, Tennessee. "It is not protection from infection -- it is protection from death."
Researchers have wondered if people who have been infected with one strain of influenza might have partial immunity to another strain. No one has complete immunity, because flu can infect the same person over and over again.
But maybe some individuals have retained just enough immunity to keep the new infection from being deadly. "The idea has been thrown around for a while and we just decided to actually test it," Webby said in a telephone interview.
