Flu Shots Less Effective This Year

October 26, 2007 · Print This Article · Email This Post

Flu Shot

As Pajamadeen sat here this week with a sore arm, having received a flu shot, she noted with interest a CTV headline regarding the suspected inefficacy of this year’s North American flu shots. A “viral mismatch” has occurred. World Health Organization (WHO) scientists monitor flu strains every year, selecting the top three strains for use in killed-virus flu shots. But this year, it appears that two of the three viruses selected for inclusion in the shots have mutated enough that they no longer match the viruses in this year’s vaccine.


These three flu strains were included in 2007 flu shots:

  • Influenza A – Solomon Islands/3/2006 (H1N1)-like
  • Influenza A – Wisconsin/67/2005 (H3N2)-like
  • Influenza B – Malaysia/2506/2004-like antigen

The Malaysian strain of the virus shows signs of changing, while the Wisconsin strain has already mutated into a different form than the one used in the vaccine, in a process known as “antigenic drift,” which involves gradual mutations in the genetics of reproducing viruses.

Dr. Neil Rau

Dr. Neil Rau, an infectious disease specialist, said that it’s “theoretically possible” that such a viral mismatch could “result in more flu illnesses and hospitalizations…The worst case scenario with a bad match situation would be a lot of disease in the elderly, manifesting in nursing home and cruise ship outbreaks, and with children you might see a lot of absenteeism and therefore a lot of parents off work as a result, trying to care for them.”


Manufacture of flu vaccines is based in part on what influenza strains appeared during the preceding season in the Southern Hemisphere and, because it requires at least six months to mass-produce the vaccines, it’s too late to change them this fall. However, flu experts say that getting vaccinated is still recommended, as antibodies produced by the vaccine will offer some immunity from whatever strains dominate. Dr. Theresa Tam of the Public Health Agency of Canada said that “In recent seasons, even where there has been a vaccine mismatch, the vaccine can afford 40-50 per cent protection.” She also noted that even a mismatched flu vaccine can “reduce the severity of the illness and complications,” especially among the elderly. According to Centers for Disease Control (CDC) statistics, about 36,000 Americans die annually from influenza.

Read more about flu.

Photo credits: CTV.ca and FrontRangeFlu.com

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