Notes from the Medical Director

Dr. Kristen Feemster
Dr. Kristen Feemster is the Medical Director of the Philadelphia Department of Public Health’s Immunization Program.

The return of the flu spray: what changed?

For the 2018-19 flu season, the Advisory Committee on Immunization Practices (ACIP) added the intranasal live-attenuated influenza vaccine (LAIV) back to the list of recommended flu vaccines for children and adults. The LAIV is a flu vaccine given as a nasal spray instead of as a shot – which a lot of patients liked.

LAIV, the flu spray, was fist introduced in 2003. It initially appeared to work really well in children, so in 2014, the ACIP made a recommendation to prefer it. But 2 years later, they changed their minds, recommending against it for the past few seasons because of LAIV’s poor effectiveness.

So what changed? Why is it being reintroduced now? Let’s take a deeper dive.

How is LAIV different from other flu vaccines?

Most flu vaccines are “inactived influenza vaccines,” or IIVs. These are made by growing the flu virus in eggs, purifying it, and then inactivating the virus – killing it. It’s then given as a shot that teaches our immune system how to respond to an actual live flu virus – even though the IIV can’t reproduce to cause a flu infection.

We’ve been using this method to make flu vaccines since the 1940s. Since the flu virus changes each year, we have to make a new vaccine each year so that the vaccine matches up with the flu strain that’s likely to emerge most strongly each year.


  • IIV: inactivated virus, given with a shot
  • LAIV: weakened virus, given with a nasal spray

Unlike the IIV, the LAIV (live attenuated influenza vaccine) is made by growing the flu virus in egg cells, and then just weakening it instead of inactivating the virus. It’s then given as a nasal spray instead of a shot – and the weakened virus can reproduce just enough to spark an immune response in a patient’s body. Though the virus is live, it’s too weak to cause infection; and since it’s administered in the nose – which is how a lot of people are exposed to the flu – it can be an especially effective way to provide protection: following the same path the disease would follow.

So why was the LAIV removed from the list of recommended vaccines in 2016?

When LAIV was first introduced, it did appear to work a little better, especially in children. So in 2014, the ACIP gave LAIV a preferential recommendation – preferring the spray over the shot.

Shortly after that – once the spray was used more widely – the ACIP’s research showed that the spray stopped working as well as it initially did. For 3 years in a row, the spray didn’t perform any better than the shot. In fact, it was less effective. So, while the CDC worked to understand what happened, the ACIP removed their recommendation for the spray (LAIV).

So what happened?

Every flu vaccine protects against 3 to 4 strains of the flu. And, the CDC found that one of the flu strains in the spray didn’t reproduce well enough to spark a good immune response in patients. Since the spray relies on weakened but live virus to reproduce in order to trigger protection in a patient, this was a problem.

This flu strain was H1N1. We had several seasons where a lot of the flu disease was due to H1N1 – so the spray just didn’t provide as much protection as originally hoped.

Okay – so now the spray is back?

Yes. Once the CDC figured out the problem with the spray, the vaccine manufacturer replaced the H1N1 strain – which wasn’t reproducing well – with another strain that works better. They also checked to make sure that there’s a good immune response to the new LAIV.

The ACIP reviewed all of the changes and felt that the problem was addressed – so the spray was added back to the list of recommended flu vaccines for anyone between age 2 and 49.

Even though the ACIP recommends the spray, the American Academy of Pediatrics recommends the shot. Why do they disagree?

When the ACIP reviewed information about the new version of the spray – including studies on the spray’s effectiveness from other countries that continued to use it – they felt that the strong immune response was a good sign that the spray should work at least as well as the shot.

The AAP was also reassured, but they wanted to see more information on protection against the actual disease before they strongly recommended it. So, they decided to recommend the inactivated vaccine (the shot) over LAIV (the spray) until we learn more about the spray’s effectiveness once it’s used more broadly.

So what should I do?

Offer both vaccines.

The effectiveness of the flu vaccine always varies from year to year as researchers try to match the vaccine to the flu virus that they expect to dominate the flu season. Despite varying effectiveness, vaccination is our best method of protection against this virus that kills tens of thousands of people in the USA each year. Since some people decline the flu vaccine because of a fear of injections, having the spray available may increase the likelihood that patients will accept the vaccine.

Patients look to us – health care providers – to listen to their concerns and make recommendations that will keep them healthy. So let’s offer them choices that can help protect them, and let’s remind them that we get our flu vaccines to protect ourselves, our children, our patients, and our community too.