Articles, Blog

July 2018 – Understanding What Happened with the Intranasal Flu Vaccine

December 7, 2019

>>Hi, my name is Paul Offit. I’m talking to you today from the Vaccine
Education Center here at the Children’s Hospital of Philadelphia. One question that I recently have been asked
here at the center is: what’s the story with the flu vaccine? How come now there is this nasal spray flu
vaccine that’s available that wasn’t available for a few years? What happened? Why did it go off the market? And why is it back on the market now? So I think the easiest way to understand this
is to start at the beginning. The first flu vaccine was actually developed
in the late 1940s. And it was made by taking influenza virus,
growing it in eggs, purifying it, and then inactivating it with a chemical so that it
couldn’t reproduce itself. And that vaccine was given as a shot. We basically have been using that vaccine
– that strategy to make a vaccine – since the late 1940s. And it’s effective at preventing pneumonia
that’s caused by influenza. Now, in 2003, there was a different strategy
used to make the flu vaccine. Now, instead of taking influenza virus and
inactivating it, this is a live, weakened form of the virus that’s not given as a
shot. It was given as a spray in the nose, where
the virus would then reproduce itself and induce an immune response without causing
disease. Now that vaccine came onto the market in the
United States in 2003. In 2014, it was actually given a preferential
recommendation by the Center for Disease Control and Prevention, or CDC, which is to say that
the CDC actually preferred the nasal spray for the vaccine to the inactivated vaccine
given as a shot. However, for three years in a row, that vaccine
underperformed the inactivated vaccine, (the vaccine given as a shot). And for that reason, although the vaccine
was still licensed and still arguably could have been purchased, because the CDC said
that they did not any longer recommend that vaccine, it basically was taken off the market. So now it’s back. And so what happened? I think the problem with that vaccine was
that one of the strains, the so-called H1N1 strain, which was actually the strain that
caused the influenza pandemic in 2009, didn’t reproduce itself efficiently. So when you give, in this case, four different
strains and inoculate it onto the lining of the nose, you have to make sure that all four
strains reproduce themselves in the same manner, the same efficiency. Otherwise, one of those strains, in this case
the H1N1 strain, didn’t reproduce itself well. And so the immune response was consistently
poor, especially when you had a predominant so-called H1N1 year. Now the company has, I think, gone a long
way to solving that problem. They’ve now proven that when they give this
vaccine to human nasal epithelial cells, the cells that line our nose, that all four viruses
replicate equally. They’ve replaced the H1N1 strain that wasn’t
replicating as well with a strain that now clearly does replicate well. They’ve shown that the immune response is
now as good as it had been in the past. So now for all practical purposes, this vaccine
has come back on the market and I suspect will be as effective as it was before it was
taken off the market and now that, I think, that they’ve solved the problem. So that’s what happened to FluMist. Thank you.

1 Comment

  • Reply Marie B. January 25, 2019 at 8:34 am

    Thank you . You explained it very well and in easy to understand words.

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