Talking About Vaccines with Dr. Paul Offit: News Briefs – July 2018 – Understanding What Happened with the Intranasal Flu Vaccine

Paul A. Offit, MD, explains the recent reintroduction of the intranasal influenza vaccine.

Visit the Vaccine Education Center to learn more about the influenza vaccine.


News Briefs — Understanding What Happened with the Intranasal Flu Vaccine

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 we’ve recently 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?

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 up 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’ve basically been using that vaccine, that strategy to make a vaccine since the late 1940s. It’s effective at preventing the 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 is 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 Centers for Disease Control and Prevention (CDC), which is to say that the CDC actually preferred the nasal spray flu 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’ve 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 onto the lining of the nose, you have to make sure that all four strains reproduce themselves in the same manner in the same efficiency. Otherwise, one of those strains, in this case the H1N1 strain, didn’t reproduce itself well, 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 the problem. They’ve now proven that when they give this vaccine onto human nasal epithelial cells, the cells that line our nose, that all four viruses replicated 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.

Now, that I think they’ve solved the problem. So, that’s what happened to FluMist®. Thank you.

Related Centers and Programs: Vaccine Education Center