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Why Not a Single Shot for All Influenza Vaccines?

Wednesday, August 26, 2009 at 11:08 AM EDT

Two different influenza vaccines will be available in the fall of 2009. One will be a trivalent preparation comprising seasonal influenza H3N2 and H1N1 strains, plus an influenza B virus strain. A monovalent vaccine will also be available against the 2009 pandemic H1N1 strain. Many readers of virology blog have asked why these four virus strains will not be combined into a single, tetravalent formulation. I posed this question to Dr. Ruben Donis, chief of the molecular virology and vaccines branch at the U.S. Centers for Disease Control and Prevention. Here is his answer.

Some of the reasons that make tetravalent influenza vaccine less attractive at this time:

  • Regulatory considerations: there have been no clinical trials with tetravalent influenza vaccines, and there is little time to do them now. Licensing without data is not a favored option. However, clinical trials for a monovalent have been started and will help establish appropriate doses, formulations, in different population groups.
  • Public health considerations: the populations at greater risk of severe outcomes are not the same for the seasonal viruses and the H1N1 – pregnant women are high on the list for receiving H1N1 vaccine.
  • Timing considerations: Seasonal vaccine will be available in September whereas pandemic H1N1 vaccine will become available later.
  • Vaccine effectiveness, adverse events, pharmacovigilance: it will be easier to monitor vaccine performance characteristics using a monovalent

He also mentioned the possiblity of making a trivalent preparation with the pandemic H1N1 strain. But he said that

…a trivalent with pandemic H1N1 would entail eliminating one of the current seasonal viruses – we don’t have evidence that any of the three seasonal viruses is becoming extinct.

I thank Dr. Donis for responding.