Amesh A. Adalja, MD, FACP, FACEP, FIDSA, August 19, 2016
In recent months, the landscape of influenza vaccine strategies has changed, with the live-attenuated nasal spray vaccine losing its status as a recommended vaccine against influenza after showing low efficacy rates in the most recent flu season. Newly published data in the Annals of Internal Medicine, however, add to the nuances of influenza vaccine recommendations.
In a study that spanned the 3 flu seasons from 2012 to 2015, children aged 3 to 15 residing in 52 Hutterite colonies were cluster randomized to receive either the trivalent injectable inactivated influenza vaccine (IIV) or the live-attenuated influenza vaccine (LAIV). The primary aim of the study was to assess whether LAIV had a superior capacity over the ordinary flu vaccine to induce herd immunity.
Overall, 1,186 children were immunized with one of the vaccines, and 3,425 other community members were not. The mean coverage of children was 76.9% in the LAIV group and 72.3% in the IIV group.
PCR-confirmed influenza infections occurred at similar rates between the groups (5.2% for IIV, 5.3% for LAIV), and no difference was noted for secondary outcomes, which included emergency department visits, antimicrobial prescription, influenzalike illness, abseentism, hospitalization, or death. Of note, children vaccinated with LAIV had a statistically higher rate of influenza A but a lower rate of influenza B.
The implications of this study are many, and future studies to establish the optimal roles that the various influenza vaccines (recombinant, high-dose, intradermal, LAIV, adjuvanted) should play during influenza season are needed. This study, in addition to showing a lack of improved herd immunity, demonstrates equivalent efficacy between the trivalent forms of IIV and LAIV. LAIV is now available exclusively in a quadrivalent formulation. Hypotheses exist that the phenomenon of viral interference among the 4 strains diminished the activity of this formulation of the vaccine in the past season. Other hypotheses exist regarding the efficacy of LAIV in populations that are highly vaccinated with the injectable influenza vaccine, such as the US. As flu vaccination options expand, it will be crucial for front-line clinicians to have clear guidance as to which flu vaccine to recommend to which patient.
Loeb M, Russell ML, Manning V, et al. Live attenuated versus inactivated influenza vaccine in Hutterite children: a cluster randomized blinded trial. Ann Intern Med 2016; published online ahead of print. doi:10.7326/M16-0513. http://annals.org/article.aspx?articleid=2543271. Accessed August 18, 2016.