Viruses shape shift, says National Institute of Health
There’s nothing like discovering that a sub-microscopic organism is smarter than pharmaceutical science. TV news reported this week that the H1N1 virus is probably already evading the Swine Flu Vaccine (SFV) which the government has rushed to anxious, uninfected people in the US.
The SFV never had a chance of stopping the flu. Scientists are talking about antigenic drift, now that people are interested in how viruses evolve. The drift takes place as a virus moves through hosts (that’s you and me), changing its proteins to evade antibodies that could kill it. At least that’s what scientists think happens. They’re not sure.
“No one is sure exactly how the antigenic drift of flu viruses happens in people,” says Dr. Jonathan Yewdell. He wrote a paper with two other experts that was published in Science, but at the moment the only hard evidence comes from testing mice with a virus from 1934. The National Institute of Health reports on the leading theory at its Web site.
According to the prevailing theory, drift occurs as the virus is passed from person to person and is exposed to differing antibody attacks at each stop. With varying success, antibodies recognize one or more of the four antigenic regions in hemagglutinin, the major outer coat protein of the flu virus. Antibodies in person A, for example, may mount an attack in which antibodies focus on a single antigenic region. Mutant viruses that arise in person A can escape antibodies by replacing one critical amino acid in this antigen region. These mutant viruses survive, multiply and are passed to person B, where the process is repeated.
These escape artists have been drifting for thousands of years. Pharmaceutical research creates a flu vaccine every year before the drift occurs. If enough people catch and then transmit a flu, the virus is well on its way to changing its shape — so only your natural immunity can hope to neutralize an organism that makes you ill once you breathe it in.