The Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP) voted Wednesday that live attenuated influenza vaccine (LAIV), also known as the “nasal spray” flu vaccine, should not be used during the 2016-2017 flu season. ACIP continues to recommend annual flu vaccination, with either the inactivated influenza vaccine (IIV) or recombinant influenza vaccine (RIV), for everyone 6 months and older.
In late May, preliminary data on the effectiveness of LAIV among children 2 years through 17 years during 2015-2016 season became available from the U.S. Influenza Vaccine Effectiveness Network. That data showed the estimate for LAIV VE among study participants in that age group against any flu virus was 3 percent (with a 95 percent Confidence Interval (CI) of -49 percent to 37 percent). This 3 percent estimate means no protective benefit could be measured. In comparison, IIV (flu shots) had a VE estimate of 63 percent (with a 95 percent CI of 52 percent to 72 percent) against any flu virus among children 2 years through 17 years. Other (non-CDC) studies support the conclusion that LAIV worked less well than IIV this season. The data from 2015-2016 follows two previous seasons (2013-2014 and 2014-2015) showing poor and/or lower than expected vaccine effectiveness (VE) for LAIV.
How well the flu vaccine works (or its ability to prevent flu illness) can range widely from season to season and can be affected by a number of factors, including characteristics of the person being vaccinated, the similarity between vaccine viruses and circulating viruses, and even which vaccine is used. LAIV contains live, weakened influenza viruses. Vaccines containing live viruses can cause a stronger immune response than vaccines with inactivated virus. LAIV VE data before and soon after licensure suggested it was either comparable to, or better than, IIV. The reason for the recent poor performance of LAIV is not known.
Vaccine manufacturers had projected that as many as 171 million to 176 million doses of flu vaccine, in all forms, would be available for the United States during the 2016-2017 season. The makers of LAIV had projected a supply of as many as 14 million doses of LAIV/nasal spray flu vaccine, or about 8 percent of the total projected supply. LAIV is sold as FluMist Quadrivalent and it is produced by MedImmune, a subsidiary of AstraZeneca. LAIV was initially licensed in 2003 as a trivalent (three-component) vaccine. LAIV is currently the only non-injection-based flu vaccine available on the market.
Yesterday’s ACIP vote could have implications for vaccine providers who have already placed vaccine orders. The ACIP recommendation may particularly affect pediatricians and other vaccine providers for children since data from recent seasons suggests nasal spray flu vaccine accounts for about one-third of all flu vaccines given to children. CDC will be working with manufacturers throughout the summer to ensure there is enough vaccine supply to meet the demand.
CDC conducts vaccine effectiveness (VE) studies each season to estimate flu vaccine effectiveness. Yesterday’s ACIP vote highlights the importance of measuring and evaluating the effectiveness of public health interventions, which can have significant implications for public health policy. The change in the ACIP recommendation is an example of using new available data to ensure public health actions are most beneficial. Influenza is a serious disease that causes millions of illnesses, hundreds of thousands of hospitalizations, and thousands or tens of thousands of deaths each year. While the protection offered by flu vaccines can vary, the flu shot’s overall VE estimate of 49 percent suggests that millions of people were protected against flu last season.
ACIP is a panel of immunization experts that advises the Centers for Disease Control and Prevention (CDC). This ACIP vote is based on data showing poor or relatively lower effectiveness of LAIV from 2013 through 2016.
CDC has recommended an annual influenza vaccination for everyone ages 6 months and older since February 24, 2010. CDC and ACIP briefly had a preferential recommendation for nasal spray vaccine for young children (during 2014-2015); however, during the 2015-2016 season, influenza vaccination was recommended without any preference for one vaccine type or formulation over another.