The Advisory Committee on Immunization Practices (ACIP) took the unusual step at its June 2016 meeting of recommending against using a currently licensed vaccine, live attenuated influenza vaccine (LAIV), in the 2016-2017 influenza season.1 ACIP based its recommendation on surveillance data collected by the US Influenza Vaccine Effectiveness Network of the Centers for Disease Control and Prevention (CDC), which showed poor effectiveness by the LAIV vaccine among children and adolescents during the past 3 years.
The US Food and Drug Administration (FDA), however, has chosen not to take any action on this matter, saying on its Web site it “has determined that specific regulatory action is not warranted at this time. This determination is based on FDA’s review of manufacturing and clinical data supporting licensure … the totality of the evidence presented at the ACIP meeting, taking into account the inherent limitations of observational studies conducted to evaluate influenza vaccine effectiveness, as well as the well-known variability of influenza vaccine effectiveness across influenza seasons.”2
CDC data for the 2015-2016 flu season showed the effectiveness of LAIV to be just 3% among children 2 years through 17 years of age.3 The reason for this apparent lack of effectiveness is unknown. Other LAIV-effectiveness studies conducted in the 2015-2016 season—one each, in the United States, United Kingdom, and Finland—had results that differed from the CDC surveillance data, with effectiveness ranging from 46% to 58% against all strains combined.2 These results are comparable to vaccine effectiveness found in observational studies in children for both LAIV and inactivated influenza vaccines (IIV) in prior seasons.2
Vaccine manufacturers had projected that 171 to 176 million doses of flu vaccine, in all forms, would be available in the United States during the 2016-2017 season.3 LAIV accounts for about 8% of the total supply of influenza vaccine in the United States,3 and ACIP’s recommendation is not expected to create shortages of other options for the upcoming season. However, the LAIV accounts for one-third of flu vaccines administered to children, and clinicians who provide vaccinations to children have already ordered their vaccine supplies for the upcoming season. Also, it is not clear if children who have previously received the LAIV product will now accept other options for influenza vaccination—all of which involve an injection.
Whether the recommendation against LAIV will continue after this season is also unknown.
What happened during the 2015-2016 influenza season?
The 2015-2016 influenza season was relatively mild with the peak activity occurring in March, somewhat later than in previous years. The circulating influenza strains matched closely to those in the vaccine, making it more effective than the previous year’s vaccine. The predominant circulating strain was A (H1N1), accounting for 58% of illness; A (H3N2) caused 6% of cases and all B types together accounted for 34%.4 The hospitalization rate for all ages was 31.3/100,000 compared with 64.1 the year before.5 There were 85 pediatric deaths compared with 148 in 2014-2015.6
Vaccine effectiveness among all age groups and against all circulating strains was 47%.4 No major vaccine safety concerns were detected. Among those who received IIV3, there was a slight increase in the incidence of Guillain-Barré syndrome of 2.6 cases per one million vaccines.7
Other recommendations for 2016-2017
Once again, ACIP recommends influenza vaccine for all individuals 6 months and older.8 The CDC additionally specifies particular groups that should not skip vaccination given that they are at high risk of complications from influenza infection or because they could expose high-risk individuals to infection (TABLE 1).9
There will continue to be a selection of trivalent and quadrivalent influenza vaccine products in 2016-2017. Trivalent products will contain 3 viral strains: A/California/7/2009 (H1N1), A/Hong Kong/4801/2014 (H3N2) and B/Brisbane/60/2008.10 The quadrivalent products will contain those 3 antigens plus B/Phuket/3073/2013.10 The H3N2 strain is different from the one in last year’s vaccine. Each year, influenza experts analyze surveillance data to predict which circulating strains will predominate in North America, and these antigens constitute the vaccine formulation. The accuracy of this prediction in large part determines how effective the vaccine will be that season.