PLEASE SHARE YOUR OPINION AND VOTE BELOW
It has always been a bit of a gamble: Predicting the main circulating flu types and subtypes for the next season based on information from the previous season is an educated guess. It works well most of the time but fails when there is no obvious selection candidate or the virus change its antigenic profile just before the new season.
As selection of vaccine candidates has to be made way ahead of the next flu season to allow for sufficient production time, this creates an approx. 6 month ‘escape’ window for viral mutations.
The 2014-2015 influenza vaccine is made to protect against the following three viruses[1]:
1. an A/California/7/2009 (H1N1)pdm09-like virus
2. an A/Texas/50/2012 (H3N2)-like virus
3. a B/Massachusetts/2/2012-like virus
It is no secret that vaccine efficacy is and will never be even close to 100%. A 50-60% level of protection is the norm. Every year CDC and health organizations admonish us to get vaccinated because available data show that disease caused by influenza A and B strains is mitigated and mortality reduced in vaccine recipients. Some but not all experts feel that even with vaccines providing mismatched, hence ‘suboptimal’ coverage there is still a benefit [2]. “Suboptimal’ is a euphemism: ‘mediocre’ seems a more appropriate term.
So far, so good.
Mismatches between vaccine strains and the circulating pool of influenza virus are inevitable. With vaccines usually containing at least 2 strains for influenza A (with 80-90% of circulating virus, this is the predominant type), not all is lost. For instance, in 2003 we had a mismatch and protection was conferred in only 36% of vaccinated non-high risk persons (see Table 1).
However, protective efficacy has never been as low as in this 2014 / 2015 flu season. Due to a major H3N2 mismatch, efficacy levels as low as 23% (first estimate), then 18% (a later estimate), and eventually 15% (for children age 2-8 years) were reported.
In light of such low coverage, why do CDC and Health Authorities still recommend in unison that we adhere to existing vaccination recommendations as in the past, why is hospital personnel still required (under threat of dismissal) to prove vaccination status?
We are told that vaccine efficacy is not to be equated with vaccine strains and that coverage is broader as long as the mismatch is less than a complete viral shift. However, not everyone agreed with CDC’s assertion that such partial coverage still reduce disease severity and mortality.[3]
This is a complex issue but here is the rub: There must be a level of protection at which point the benefits no longer outweigh the risks (and costs) of the effort. If this break point is less than 18%, as current CDC endorsement indicates, is it at 15%, 10% or as low as 5%? Trying to get this question answered proved more difficult than expected.
I was hoping to find some literature, an analysis that would provide the answer. Unfortunately, this was not the case. Before calling the experts at the CDC, I would like to hear from you. Please vote below and/or leave a comment below – thank you!
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References:
[1] http://www.cidrap.umn.edu/news-perspective/2014/12/cdcs-flu-warning-raises-questions-about-vaccine-match
[2] A Tricco Tricco et al. BMC Medicine 2013, 11:153
[3] http://www.cdc.gov/flu/professionals/vaccination/virusqa.htm
