The US has released preliminary results of their vaccine effectiveness estimates for the 2012-2013 influenza vaccine, based on five study sites. They found that vaccine effectiveness was 62% at preventing influenza-associated medical visits (55% for influenza A and 70% for influenza B). The analysis has not yet been done by age. 

Although not perfect, a vaccine effectiveness of 62% is still important. It means that more than half of people who would otherwise get sick, will not get sick because of being vaccinated. Because influenza is very common (especially this year), this means that a lot of people will not get sick because of being vaccinated. 

Additional information:

Vaccination effectiveness varies with the match of the strains to the circulating virus (which is matching very well for influenza A this year), along with the age and health status of the patient. Healthy younger adults tend to have higher effectiveness estimates than older adults or those with problems with their immune system. A Cochrane review estimated the effectiveness in healthy adults at 80% (95% CI 56% to 91%) when the vaccine strain matched the circulating strains and circulation was high.

It should be noted that the herpes zoster vaccine has similar efficacy estimates (51% at preventing shingles and 67% at preventing post-herpetic neuralgia).

Bryna

References

Public Health Agency of Canada. Statement on Seasonal Influenza Vaccine for 2012–2013 Retrieved from
http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/12vol38/acs-dcc-2/index-eng.php