Question special
Lead Moderator

Thank you to our panelists for the great discussion about the live attenuated influenza vaccine (LAIV). To build on some of the points that were already made, the next question relates to the the varying effectiveness of LAIV between populations.

As noted by Dr. Cowling, in contrast to the US, in the UK the LAIV has been shown to be effective against influenza A(H1N1)pdm09. Similarly, in a recently published cluster randomized controlled trial among Hutterite children in Canada (Loeb et al., Ann Intern Med 2016), LAIV was non-inferior to inactivated influenza vaccine (IIV) when analyzed across all influenza subtypes. However, in this trial the LAIV vaccinated individuals did experience more influenza A infections compared to IIV vaccinated individuals, but this difference seems to have been driven largely by influenza A(H3N2) and not A(H1N1)pdm09. Of note, in the latter study, the investigators used LAIV3 because the quadrivalent vaccine was unavailable.

What could account for the varying performance of LAIV across diverse settings/populations?