Flu vaccines may not be as effective as we thought

Every year I get the current vaccine against influenza; the risk is extremely low, the discomfort is very low and I really hate having 2 weeks of fever. Yes, for some people influenza is nothing but not for me. But a paper that came out last year had trouble finding a real effect from the vaccines when looking at hospitalisations or mortality:

Our results showed a sharp increase in influenza vaccination rates at age 65 years with no matching decrease in hospitalization or mortality rates.


Two factors could explain how the vaccine might reduce influenza but not more serious outcomes. First, only a minority of hospitalizations or deaths may be attributable to influenza. A recent study estimated that only 2% to 10% of pneumococcal cases over an entire year are caused by influenza. Even if the influenza vaccine achieved50% effectiveness among elderly persons, the net reduction in pneumococcal cases would be only 1% to 5%, which lies within the CIs of our estimates for this outcome. Nevertheless, during peak influenza season, the fraction of pneumococcal cases caused by influenza may reach 40%, and our analysis focused on the October-to-March period.

A second factor that may help explain our results is immune-response heterogeneity. The influenza vaccine is less effective in immunocompromised persons, who also face the highest risk for serious influenza-related complications. Thus, even if the influenza vaccine were effective at reducing influenza-like illness for the typical elderly recipient, it would be less effective among elderly persons at high risk for hospitalization or death. Heterogeneity in immune response among elderly persons could therefore reconcile effectiveness against influenza-like illness with less effectiveness against more serious outcomes.

In conclusion, our results do not preclude modest effectiveness of the influenza vaccine against severe outcomes in elderly persons. Therefore, continued vaccination of this population, particularly with high-dose vaccines, seems appropriate. Our findings raise questions, however, about the overall effectiveness of a vaccination strategy that is limited to standard vaccines and focuses too much on elderly persons. Supplementary strategies, such as vaccinating children and others who are most likely to spread influenza, may also be necessary to address the high burden of influenza-related complications among older adults.

Which is interesting and certainly warrants further research.















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