The H1N1 pandemic virus that took the world by storm in 2009 may
have had an unexpected accomplice. Some of the thousands who
died may have been victims of their own immune systems, suggests
a paper appearing in Nature Medicine today. The study provides a
possible answer to one of the most baffling questions since the
virus appeared in the spring of last year: Why did the virus
cause most damage in 20- to 50-year-olds—who are generally the
healthiest—while sparing the very young and the very old?
Influenza pandemics occur when a totally new strain of the virus
emerges, against which nobody's immune system is fully prepared;
that's why both the healthy and the weak are vulnerable. But
that doesn't explain why senior citizens, with generally weaker
immune systems, and young children, with no immunity to
influenza whatsoever, tended to get cases of H1N1 that were
milder than their healthier counterparts. "In a middle-aged
population, we saw a lot of people getting very, very ill," says
pediatrician Fernando Pola