Like we need one more thing to be worried about this year during the flu season?

One of the components of the annual seasonal flu vaccine may not be well matched for a new variation (or drift) of the good old standard H3N2 virus which is included as part of these combination vaccine. Some samples of the emerging new strain of H3N2 viruses show a substantially reduced response to antibodies generated by the corresponding virus in the seasonal vaccine, raising the possibility of significantly reduced protection in some cases.

Oh great…

Vaccine mismatches do happen

Vaccine mismatches do happen and are never good.  However in the middle of a global influenza pandemic of a new novel strain (H1N1), to have your seasonal flu vaccine not be a good match means more illness, hospitalizations and deaths This would be amongst the more traditional age groups – older and the very young.   So the H1N affects children to young adults, the H3N2 the very young and older adults…something for everyone!

Egg-Based Vaccine Production
Egg-based Vaccine Production

The new variant has been seen on a number of continents, though it still remains a minority member of the H3N2 family, according to experts at the World Health Organization and the U.S. Centers for Disease Control in Atlanta.  The next month or so will likely tell the story as to whether the pandemic virus will crowd out the previous influenza A subtypes – making the composition of the seasonal vaccine less relevant – or whether one or both of the seasonal flu A virus families will continue to circulate.

How could this happen?

Because it takes months to make and ship flu vaccine, the viruses covered by the seasonal flu shot have to be chosen long in advance. In the Northern Hemisphere vaccine, flu experts met in February to assess the viruses circulating and make their best estimates of which will be the major disease sources in the following winter.

For this flu season, 2009-2010 winter, they chose an H3N2 virus called A/Brisbane/10 first identified in 2007.  But within weeks of the decision hints emerged there was a new H3N2 variant, one sufficiently mutated (the medical term is “drifted”) that it might be able to evade the vaccine.

Researchers in the influenza lab at the British Columbia Centre for Disease Control spotted it in early March as they were conducting late-season surveillance looking for just such viral evolution. In early May, they reported the finding on ProMed, an electronic bulletin board and mailing list which monitor infectious diseases outbreaks around the world.  Dr. Danuta Skowronski, an influenza expert at the BCCDC, said she is expecting this new variant to take over as the dominant H3N2 strain. And since the swine flu virus isn’t infecting older adults much, it could leave a niche for the new H3 variant.

Net – Net…what does this mean?

We just have to prepare for a worse case scenario…. The seasonal flu is a poor match and the pandemic vaccine is not available early enough or in large enough quantities.

“The idea of having a mismatched drift strain circulating the same year that we also have swine influenza may mean that all segments of the population are affected by influenza one way or the other, whether it’s the elderly with H3N2 and the young with H1N1.”

Buckle up.

If you would like to do some detailed reading on the national influenza vaccine program and vaccine preparation check out this report issued July 24, 2009 from CDC