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Mystery Rays from Outer Space
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| HA structure showing mutating amino acids1 |
Anyone who’s taken a virology class, and many who haven’t, know about “antigenic drift” and “antigenic shift”. These are usually used to explain influenza virus changes over time (although of course the same concepts apply to many other viruses). Antigenic shift refers to large, abrupt changes in the virus;2 antigenic drift refers to smaller changes. Antigenic shifts are associated with pandemic influenza, as the pre-existing immune responses to influenza from previous years aren’t protective any more (because the virus has shifted away from them). Antigenic drift doesn’t let the virus escape immune control altogether, but does give the virus an advantage in infecting people — presumably, people with strong responses are still protected, but those whose exposure was maybe a few years ago, or who happened to make a weaker antibody response, to the previous virus, would be susceptible to the new virus but protected against the original. Antigenic drift happens all the time, and new drifted variants of influenza take over every year or two, which is why we need new seasonal flu vaccines on a regular basis.
What drives antigenic drift? The simple answer is that it’s driven purely …