QUESTIONS AND ANSWERS
Andrew Pekosz, an associate professor of molecular microbiology and immunology at Johns Hopkins University's Bloomberg School of Public Health in Baltimore, answers questions about swine flu.
-- Shankar Vedantam
If a person is no longer infected with the flu because the infection has run its course, the virus will not show on a test. But wouldn't other tests show antibodies to that virus?
If you have been infected with swine H1N1, then you will have acquired antibodies against the virus that should protect you from future infection with the same strain. A test specific for swine H1N1 antibodies has not been developed to date, though several groups are working on it. The only test we have at this time for swine H1N1 requires live virus to be present.
Why does the flu primarily circulate during winter? Is there any reason to believe that the current outbreak of H1N1 would necessarily be reduced in severity because of the season? Does that imply that even if there is no pandemic at this time, there could be a more serious one (of the same flu) next winter?
We have some ideas about why influenza spreads in winter. Low humidity and temperatures are optimal for the spread of aerosol particles, and people are in close quarters inside, so there is a greater chance that they will come in contact with an infected person. There are a lot of things we don't know, however. The swine H1N1 virus may be slowing down because of the spring weather as well as the public health measures that have been put in place. If the virus has established itself in the human population, then it will return in the fall.
How will we know that? If there are no cases in the Southern Hemisphere, could the virus still find a reservoir and survive until the winter?
The coming influenza season in the Southern Hemisphere will be important to monitor. Influenza viruses move from the Northern Hemisphere to the temperate zones to the Southern Hemisphere and back again. If we find swine H1N1 flu in the temperate zones, and it emerges in the Southern Hemisphere (remember, when it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere), then there is a very good chance the virus will be with us to stay.