Just as publicity about the need for everyone to get a flu shot ramps up, there are signs that the influenza vaccine for this “flu season” (2019-2020) may be even less effective this year than last year. The strains of the influenza virus selected by the World Health Organization (WHO) and U.S. health officials for vaccine manufacturers to include in this year’s flu shot for the North Hemisphere (including the United States) may turn out to be a ‘mismatch,’ according to epidemiologist Danuta Skowronski, MD of the British Columbia Center for Disease Control in Vancouver, Canada.1 2
In February 2019, the WHO recommended the “influenza B virus component of trivalent vaccines for use in the 2019-2020 northern hemisphere influenza season be a B/Colorado,” and the A(H3N2) component in March. In September, the WHO selected different A/H3N2 influenza virus strains for the Southern Hemisphere, suggesting to Dr. Skowronski that the earlier strain prediction may be wrong.3 4
Dr. Skowronski told Scientific American, “I think the vaccine strain selections by the WHO committee are obviously important for the Southern Hemisphere but they’re also signals to us because they’re basing their decisions on what they see current predominating on the global level.”1 2
“There was great uncertainty around which version of H3N2 to choose for the Northern Hemisphere vaccine when the committee met last February—there was a lot of variation between the strain the U.S. was seeing and the H3N2 viruses sickening people in Canada and Europe,” writes journalist Helen Branswell for Scientific American. “There was so much uncertainty, in fact, that the [WHO] committee delayed making the choice of the H3N2 strain for a month to try to get a clearer picture.”1
It appears now that the WHO’s earlier prediction might end up being “off the mark,”1 which means that the flu shot this season could be less effective than it was last year. The U.S. Centers for Disease Control and Prevention (CDC) estimated that influenza vaccine was only 29 percent effective during the 2018-2019 flu season and only nine percent during the second half of the season.5
CDC estimates for the effectiveness of the flu shot usually range between 40-50 percent. During the 2004-2005, 2005-2006 and 2015-2016 flu seasons, the vaccine was only 10 percent, 21 percent and 19 percent effective respectively.5
“Every year, they basically have to guess which influenza strains are going to be most prevalent, because the influenza virus changes rapidly,” Barbara Loe Fisher of the National Vaccine Information (NVIC) told The Washington Post in June 2019. “Historically, they’ve had a problem ever since the influenza vaccine was first used decades ago. They’ve had a problem with getting it right, and this is a recurrent problem.”6
1 Branswell H. Flu Vaccine Selections Suggest This Year’s Shot May Be Off the Mark. Scientific American Sept. 30, 2019.
2 Rahhal N. Another flu shot fail? This season’s vaccine for the US, UK and Canada is likely to be a ‘mismatch’ for the deadly virus, expert warns. Daily Mail Sept. 30, 2019.
3 World Health Organization. Recommended composition of influenza virus vaccines for use in the 2019-2020 northern hemisphere influenza season. WHO.int Mar. 21, 2019.
4 New Flu Strains for 2019-2020 have been Identified. FluShotsForYou.com.
5 Cáceres M. What’s So Effective About a Flu Vaccine That’s Less Than 10 Percent “Effective”? The Vaccine Reaction July 3, 2019.
6 Wu Tan S. 2018 flu shot was less effective, says health report. The Washington Times June 27, 2019.