'Original Antigenic Sin': A threat to H1N1 vaccine effectiveness?

[indigo girl]

I know. I know. It gives all of us a headache to learn of yet another immune system phenomenom that may affect whether or not the new vaccines will work...

Who knew it was all going to be so complicated?

Half a century ago, scientists reported evidence of some curious behavior by the immune system in humans and animals: If a host was exposed to an influenza virus and later encountered a variant strain of the same virus, the immune system responded to the second attack largely with the same weapons it used against the first one.

Like an army still fighting by the tactics of the last war, the host immune system mostly produced antibodies matched to the first virus instead of the second, resulting in a less effective defense. With a nod to theology, this phenomenon was labeled "original antigenic sin."

Today, in the face of the pandemic H1N1 flu virus, many countries are preparing to launch H1N1 vaccination campaigns this fall. Millions of people are in groups recommended to receive both seasonal flu immunizations and H1N1 vaccinations. Seasonal flu vaccine--which contains an H1N1 component, distantly related to the novel H1N1 virus--will be available sooner in most places.

This timing has caused some observers to wonder: If a person gets a seasonal flu shot and then an H1N1 dose a few weeks later, will original antigenic sin come into play and cause a poor response to the H1N1 vaccine?

Nobody knows the answer for sure, but leading flu and immunization experts say they aren't especially worried at this point. At the same time, they suggest the possibility bears watching.

...there is enough concern so that the H1N1 vaccine clinical trials recently announced by the National Institute of Allergy and Infectious Diseases (NIAID) will look into the question. Two of the trials will examine whether giving an H1N1 vaccine and seasonal flu vaccine sequentially or simultaneously affects the immune response to either vaccine, according to the NIAID's descriptions of the trials.

Read on: http://www.cidrap.umn.edu/cidrap/content/influenza/swineflu/news/aug1809originalpwm.html

[oramar]

There is a possibility that there may be so little vaccine ready that it will become a moot question.