Hi. My name is Paul Offit. I'm talking to you from the Vaccine Education Center at Children's Hospital of Philadelphia. What I want to talk about today is the influenza virus's elusiveness—specifically, that it's elusive in three ways. First is that every year, the hemagglutinin (the cell attachment protein that sits on the surface of the virus) mutates. It mutates so much from one year to the next, that immunization or natural infection one year doesn't protect against disease the following year. For that reason, everyone over 6 months of age in the United States is recommended to receive an influenza vaccine.
The way that the influenza strains are picked is that every year, the strains that are circulating in South America are recognized by the US Food and Drug Administration and then are included in the vaccine. Sometimes, however, as those viruses travel from South America to North America, they mutate—so much so, that they mutate away from the strains that were included in the vaccine. That's what happened in the 2014-2015 season, when the efficacy of the flu vaccine was only 13%. And that was because 80% of the strains that were circulating in the United States that year were variant to the strains that were originally included in the vaccine—the so-called H3N2 variant strains.
The third way that influenza virus mutates is during manufacture; specifically, manufacture in eggs. This doesn't really happen in mammalian cells; it doesn't happen with recombinant DNA-technology vaccines, but it does happen when the virus can grow in eggs, and that, apparently, might have been what happened to explain the only 42% efficacy that we saw last year, during the 2016-2017 season. Now, with that said, if you look at the number of deaths that have been prevented by the influenza vaccine between the 2005-2006 season and the 2013-2014 season, we have saved an estimated 40,000 lives with the influenza vaccine. The efficacy of the influenza vaccine when you don't get it is 0%, and 40% is better than 0%. So although the vaccine isn't perfect, it's still of value and therefore should be used. Thank you.
Medscape Infectious Diseases © 2018 Children's Hospital of Philadelphia and Medscape
Cite this: A Bad Flu Year: Lives Are Saved Even With a 'Less Effective' Vaccine - Medscape - Jan 30, 2018.