Even though we have just gotten over a heat wave and still expect more warm weather to come, it’s that time of the year where flu shots become available, and getting one “sooner than later” is often recommended (especially for our older population). I’d like to summarize some recent scientific/medical papers that have presented new data about Influenza A & B, as well as flu shot efficacy and timing.
The first series of articles deals with shedding of Influenza viruses by infected people:
This year’s flu season, according to the CDC, was marked by an overall limited protection from the flu shot. This was due to the fact that the H3N2 strain (a Type A Influenza virus) was the dominant one. It accounted for 58% of all Influenza virus subtypes, and there was not a match with the flu shot given. This resulted in an overall efficacy against the A subtypes of only 30%. Although the match for type B influenza viruses was good, they only accounted for 31% of the circulating virus subtypes. Consequently, the overall efficacy for the vaccine this past season was only 38% (adjusted for all ages). Nonetheless, the CDC stated the vaccine likely prevented upwards of 90,000 hospitalizations due to the flu (CIDRAP News, July 02,2019, http://www.cidrap.umn.edu/news-perspective/2019/07/poor-late-season-protection-limited-flu-vaccine-impact-2018-19).
Looking at other CDC data for the period October 1, 2018-March 30,2019 (https://www.cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm), there were approximately 38 million cases of influenza, nearly 18 million flu-related medical visits, upwards of 549,000 hospitalizations due to the flu, and upwards of ~51,000 flu-related deaths.
A series of articles looked at how effective the flu shot is:
So, what do we conclude from all of these articles? Flu shots significantly reduce the risk for influenza-related hospitalizations and complications, getting yearly flu shots also reduces risk for a severe infection (independent of efficacy of the vaccine), high dose is more effective that standard-dose shots in the elderly, protection from the flu (efficacy) wanes as the season progresses, and delaying the flu shot until the late fall may make sense (but there are risks that “flu season” could begin earlier than expected). The final message is- get your flu shot, there is no reason not to!!!