February 21, 2019
2 min read

WHO delays picking H3N2 virus for next season’s flu vaccine

You've successfully added to your alerts. You will receive an email when new content is published.

Click Here to Manage Email Alerts

We were unable to process your request. Please try again later. If you continue to have this issue please contact customerservice@slackinc.com.

The WHO advisory group that recommends which influenza viruses should be included in seasonal vaccines said it would wait another month, until March 21, to select an H3N2 component for the Northern Hemisphere’s 2019-2020 vaccines “in light of recent changes in the proportions of” circulating viruses.

Delaying the recommendation for H3N2 — an influenza A subtype that is notoriously difficult to protect against and generally portends more serious seasons when it predominates, like the one that occurred last year in the United States — “will allow more time for monitoring virus circulation and characterization of appropriate vaccine viruses,” WHO said.

A WHO spokesman told Infectious Disease News that, to his knowledge, it was the first time since 2003 that the group delayed making a vaccine recommendation while it waited for more information.

In the U.S., the FDA committee that effectively picks what viruses will be included in influenza vaccines — relying on WHO’s recommendations — is scheduled to meet on March 6. An FDA spokeswoman told Infectious Disease News that the meeting will be held as planned to vote on the recommendations that WHO made for the other vaccine components, and that a subsequent meeting will be held when the H3N2 recommendation is made.

It is unclear whether this will delay production of influenza vaccines meant to be distributed in the U.S. Vaccine manufacturers Seqirus and GlaxoSmithKline did not immediately respond to requests for comment, and a representative for Sanofi Pasteur was unavailable to comment.

Also unclear is whether vaccine recommendations previously made for the Southern Hemisphere are still appropriate with a new influenza season just a couple of months away. A WHO spokesman said vaccine production in the Southern Hemisphere “is fully ongoing” and that the next composition meeting to determine the 2020 vaccine will take place in about 6 months.

The WHO group recommended in September that manufacturers in the Southern Hemisphere swap out last year’s H3N2 component — A/Singapore/INFIMH-16-0019/2016 — for an A/Switzerland/8060/2017-like virus. WHO said the egg-grown versions of those vaccine viruses are not currently working well against most recent H3N2 viruses in experiments using ferret antisera.

WHO’s recommendations for the other vaccine components in the Northern Hemisphere included one change from last year: switching the H1N1 component from A/Michigan/45/2015 to an A/Brisbane/02/2018-like virus, which are currently predominating. This differs from the recommendation for the Southern Hemisphere’s vaccine, which includes the Michigan virus.


In the Northern Hemisphere, WHO recommended quadrivalent influenza vaccines also contain a B/Colorado/06/2017-like virus and a B/Phuket/3073/2013-like virus, like last year. In addition to two influenza A viruses, the group recommended that trivalent vaccines continue to include a B/Colorado/06/2017-like virus. – by Gerard Gallagher


WHO. Recommended composition of influenza virus vaccines for use in the 2019-2020 Northern Hemisphere influenza season. https://www.who.int/influenza/vaccines/virus/recommendations/201902_recommendation.pdf?ua=1. Accessed February 21, 2019.

WHO. Questions and answers. https://www.who.int/influenza/vaccines/virus/recommendations/201902_qanda_recommendation.pdf?ua=1. Accessed February 21, 2019.