For the 2018-19 flu season, the Advisory Committee on Immunization Practices has added the intranasal live-attenuated influenza vaccine (LAIV) back to the list of recommended flu vaccines for children and adults. The ACIP recommended against LAIV for the past few seasons because of poor effectiveness. Why is it being reintroduced now?
How is LAIV different from inactivated influenza vaccines (IIV)?
Inactivated influenza vaccines are made by growing influenza viruses in eggs, purifying the virus then inactivating, or killing the purified virus. It is given as a shot and leads to an immune response that will give us protection, but the inactivated virus cannot reproduce to cause infection. We have been using this method to make flu vaccines since the 1940s. The flu virus changes a little each year so we have to make a new vaccine to make sure we get a good match.
LAIV is made by growing influenza virus in egg cells then weakening it. It is given as a nasal spray so that the weakened virus can reproduce just enough to spark an immune response and give us protection, but the live virus is too weak to cause disease. Because LAIV sparks an immune response in the nose where we are also exposed to influenza, it could be an especially effective way to provide protection
Why was 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, in other words, the ACIP preferred LAIV over the inactivated vaccine. But shortly afterwards, when the ACIP noticed that LAIV stopped working well. For 3 years in a row, LAIV did not perform any better than IIV- in fact it had lower effectiveness. While the CDC worked to determine why LAIV wasn’t working well, the ACIP removed their recommendation for LAIV.
It turned out that one of the flu strains in LAIV (every flu vaccine protects against 3 or 4 strains) did not reproduce well enough to spark a good immune response- so protection was not very good either. The affected strain was H1N1 and we happened to have flu seasons with a lot of H1N1.
Why is LAIV now available again?
Once the problem with LAIV was recognized, the vaccine manufacturer replaced the H1N1 strain that wasn’t reproducing well with another one that works better. They also checked to make sure that there is a good immune response to the new LAIV for all of the included strains. The ACIP reviewed all of this information and felt that the issue was resolved and LAIV was added back to the list of recommended influenza vaccines for anyone between 2 and 49 years of age.
Even though the ACIP has recommended LAIV for 2018-19, I read that the American Academy of Pediatrics still prefers the inactivated vaccine. Why is there a discrepancy?
When the ACIP reviewed information about the new LAIV, they felt that the strong immune response was a good indicator that the vaccine should work at least as well as the inactivated vaccine so should be available for administration. The ACIP also reviewed studies on LAIV effectiveness from other countries who had continued using LAIV and found these studies to be reassuring. The AAP was also reassured that the new LAIV leads to a strong immune response, but they wanted to see more information on protection against actual disease before strongly recommending LAIV. For that reason they decided to recommend a preference for the inactivated vaccine until we learn more about actual LAIV effectiveness.
So what should I do?
The new LAIV addresses the problem that made LAIV show poor effectiveness and leads to a good immune response which is a sign of good protection. Flu vaccine effectiveness always varies each year due to the match between our vaccines and circulating influenza types- but vaccination is still our best method of protection. Since the fear of injections is one reason some people decline flu vaccines, availability and use of LAIV may help increase the likelihood that some patients say yes to flu vaccines.