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ACIP recommends against using LAIV in US
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In June, the CDC’s Advisory Committee on Immunization Practices, or ACIP, voted not to recommend the live-attenuated influenza vaccine, or LAIV, for use in the United States during the current influenza season. The decision was based on data showing the vaccine — offered as the nasal spray FluMist (MedImmune) — had been ineffective over the past three seasons.
Infectious Diseases in Children asked Brendan Flannery, PhD, epidemiologist in the CDC’s Influenza Division, to better explain why LAIV was not recommended in the U.S. and whether data from countries that chose to continue using it, such as Canada, would have a role in next year’s recommendation.
In light of low effectiveness against the influenza H1N1 strain (A[H1N1]pdm09) in the United States during two recent influenza seasons (2013-2014 and 2015-2016), ACIP made the interim recommendation that LAIV should not be used for the 2016-2017 season. The 2016-2017 LAIV vaccine contains the same H1N1 strain as the 2015-2016 LAIV quadrivalent vaccine that showed low effectiveness. ACIP heard data from the U.S., United Kingdom and Finland, and took those data into account when making the decision for the U.S. ACIP’s decision was based primarily on the low effectiveness of LAIV against the 2009 pandemic H1N1 virus that continues to cause substantial disease and death. However, LAIV provided protection against other influenza viruses in some studies. The reason for the poorer performance of LAIV is not well-understood and is a subject for further study.
It is possible that several factors could be influencing how well the vaccine works:
- The live-attenuated H1N1 virus in the vaccine (which was updated for the 2015-2016 LAIV vaccine) may not generate a protective immune response, or the response might be diminished by competition with the other live-attenuated viruses in LAIV.
- The immune response to LAIV might be dampened by prior vaccination. Pre-licensure trials that showed better protection from LAIV were conducted in children who had not been vaccinated. Many U.S. children now get vaccinated before they are 2 years of age (before they receive LAIV), and this may influence the immune response to LAIV.
Other countries continue to use LAIV this season. Data from these countries will be considered in making U.S. recommendations for the 2017-2018 influenza season. Influenza vaccines are our first line of defense against the disease and it is important that recommendations are based on the best evidence. Influenza shots continue to offer substantial protection against illness.
Disclosure: Flannery reports no relevant financial disclosures.