Time to postpone the seasonal vaccine?

Here is an edited excerpt from a post on the ClinMicroNet, a listserve for clinical microbiologists. The author is with the Ontario Public Health Labs and has seen the Canadian data we’ve blogged about here and here.

Yes, unfortunately the study is still under review--however it is the worst kept secret in the country. Basically, data derived from a cohort of patients in a vaccine efficacy study that has been ongoing for a number of years has shown that persons under 50 that got seasonal vaccine last year were at 2X the risk of getting H1N1. Data looks very compelling and although never seen with influenza (no one has had opportunity to look) there is other viral precedents (antibody dependent enhancement). As a result Ontario (and probably most provinces will follow) will first vaccinate those >65 (and nursing home residents)---they are least susceptible to getting H1N1 but at greatest risk for H3N2—and then provide H1N1 for high risk people, and then for everyone else. Then decision will be made re rollout of seasonal vaccine, if at all.

If you take into account these admittedly preliminary (and unconfirmed) findings, the fact that over 95% of influenza A viruses being typed in the U.S. right now are H1N1, and the imminent availability of the novel H1N1 vaccine, you have a strong argument for taking the approach described above—reverse the order of vaccination, get H1N1 vaccine out first, and worry about the seasonal vaccine later…….