Each year, vaccine makers study antigenic and genetic characterization of influenza viruses to determine vaccine components for the upcoming flu season. It is impossible to predict which influenza virus will predominate to cause illness outbreaks each year, due to the potential for antigenic drift from season to season. When influenza A (H3N2) viruses collected in late summer of the 2014-2015 season showed significant antigenic shift compared to that year’s recommended vaccine, it signaled that there would be a low level of vaccine effectiveness for the coming flu season.
Twice a year, the World Health Organization
sponsors a vaccine consultation meeting, where world health leaders meet to review influenza surveillance data and determine vaccine components. At the February 2016 meeting, attendees selected the components for the 2016-2017 Northern Hemisphere influenza vaccine. Since then, the CDC’s laboratory-based studies of approximately 5,000 influenza viruses found that most circulating viruses do not have significant changes and have been characterized antigenically, genetically, or both as being similar to the reference viruses representing vaccine components recommended. This gives a good indication on this season’s influenza vaccine's ability to produce an immune response against circulating influenza viruses.
The CDC recommends
getting a flu shot as the best way to avoid an influenza infection each season. Vaccines need to be given each year as the immunity goes away over time and the components of a previous season’s vaccine may not offer adequate protection from viruses circulating in following seasons. While the effectiveness of the vaccine can vary, flu shots reduce the number of influenza-related illnesses, doctor visits, and hospitalizations.
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