Two components of the trivalent and quadrivalent influenza vaccines used during the current season should be replaced for the 2015-2016 vaccine, including the influenza A (H3N2) component, a Food and Drug Administration advisory panel has stated.
During the current season, most of the influenza activity in the United States has been due to influenza A (H3N2), and more than two-thirds of the A (H3N2) viruses tested at the Centers for Disease Control and Prevention have “drifted” from the A (H3N2) strain included in the current vaccines, reducing their effectiveness.
The FDA’s Vaccines and Related Biological Products Advisory Committee voted at a meeting March 4 to recommend that the following viruses be used for the 2015-2016 trivalent vaccine: an A/ California/ 7/ 2009 (H3N2) pdm09-like virus; an A/ Switzerland/ 9715293/ 2013 (H3N2)-like virus; and a B/ Phuket/ 3073/ 2013-like virus (B/ Yamagata lineage). The A (H3N2) strain and the B/ Yamagata lineage strain would replace the strains in the current vaccine.
The committee recommended a B/ Brisbane/ 60/ 2008-like virus (B/ Victoria lineage) for the second influenza B strain in the quadrivalent vaccine, which is included in the current quadrivalent vaccine. The panel votes separately on the strains; all votes were unanimous, except for the vote on the B/ Yamagata lineage strain in the trivalent vaccine, which was supported by a 14-1 vote.
The FDA panel’s recommendation is the same as the recommendation made recently by the World Health Organization for next season’s influenza vaccines in the Northern Hemisphere. Every year, the FDA panel meets at this time and considers the WHO recommendation, as well as information that includes influenza surveillance and epidemiology data in North America and worldwide.
This season has been “moderately severe” and started about 4 weeks earlier than average, peaking in late December and early January, according to Dr. Lisa Grohskopf of the epidemiology & prevention branch in the CDC’s influenza division.
Hospitalization rates for laboratory-confirmed influenza this season have been markedly higher among people aged 65 years and older, compared with younger age groups. As of Feb. 21, the preliminary estimate of hospitalizations in this age group was 51.7 cases per 100,000 people, compared with about 27 per 100,000 during the last season. This is the highest rate recorded for this age group since surveillance began during the 2005-2006 season.
To date, there have been 92 pediatric deaths associated with influenza, compared with 109 reported during the 2013-2014 season, 171 during 2012-2013, and 37 during 2011-2012.
When asked why the hospitalization rate has been so high among the elderly, it was said that A (H3N2)-predominant seasons tend to be associated with more severe disease, and vaccine efficacy this season was reduced.
The data for the pediatric deaths are incomplete, but most of these cases have been associated with influenza A, and the subtypes tested have been A (H3N2). Whether they represent drifted strains is not yet known, she said. The children’s vaccination status also is not yet known, but historically about 85%- 90% of influenza-associated deaths in children are in those who were not vaccinated.
Updated estimates of the current vaccine effectiveness against influenza A (H3N2) viruses, provided by the CDC on Feb. 26, is 18%. For all influenza viruses overall, estimated effectiveness is 19%, indicating that the flu vaccine reduced a person’s risk of having to seek medical care at a doctor’s office for flu illness by 19%, according to the update. During seasons when the vaccine is a good match for circulating viruses, vaccine effectiveness is in the 60% range, according to speakers at the FDA panel meeting.