#13,909
Although the global fluscape is constantly changing, and flu activity always varies greatly around the world, it is fair to say things are a bit more up in the air than usual as we slide into March.
So much so, that two weeks ago the World Health Organization delayed their decision on which H3N2 vaccine component to add to next fall's seasonal flu shot until later this month.This delay was sparked by the very rapid rise and spread of an H3N2 clade 3C.3a virus around the world - including in the United States (see CDC FLuView Week 8: Flu Remains Elevated - H3N2 Clade 3C.3a Continues Rise) - that differs antigenically from the current vaccine virus.
Additionally, Australia has been reporting an unusual number of `summer flu cases' in the past few months (see today's Virology Down Under Blog by Dr. Ian Mackay), although it isn't clear whether this increase is due to increased testing or a change in the level of viral activity.
Yesterday the WHO published their latest global influenza report, that touches on both of these issues (bolding mine).
Influenza update - 336
04 March 2019 - Update number 336, based on data up to 17 February 2019
Information in this report is categorized by influenza transmission zones, which are geographical groups of countries, areas or territories with similar influenza transmission patterns.
Summary
In the temperate zone of the northern hemisphere influenza activity continued to increase.
- In North America, influenza activity continued to increase in the United States of America, with influenza A(H1N1)pdm09 as the dominant subtype, followed by influenza A(H3N2).
- In Europe, influenza activity remained elevated across the continent and was reported as widespread in most of the countries. Influenza A viruses co-circulated.
- In North Africa, influenza activity remained elevated.
- In Western Asia, influenza activity peaked is some countries and increased in other, with all seasonal influenza subtypes co-circulating.
- In East Asia, influenza activity appeared to decrease overall, with influenza A(H1N1)pdm09 virus predominating.
- In Southern Asia, influenza activity remained elevated overall with influenza A viruses predominating.
- In the Caribbean, Central American countries, and the tropical countries of South America, influenza and RSV activity were low in general.
- In the temperate zones of the southern hemisphere, influenza activity remained at inter-seasonal levels, with the exception of some parts of Australia where influenza activity remained above inter-seasonal levels.
- Worldwide, seasonal influenza A viruses accounted for the majority of detections.
National Influenza Centres (NICs) and other national influenza laboratories from 115 countries, areas or territories reported data to FluNet for the time period from 04 February 2019 to 17 February 2019 (data as of 2019-03-01 05:22:16 UTC). The WHO GISRS laboratories tested more than 220347 specimens during that time period. 74302 were positive for influenza viruses, of which 73225 (98.6%) were typed as influenza A and 1077 (1.4%) as influenza B. Of the sub-typed influenza A viruses, 19600 (65.2%) were influenza A(H1N1)pdm09 and 10447 (34.8%) were influenza A(H3N2). Of the characterized B viruses, 82 (26.2%) belonged to the B-Yamagata lineage and 231 (73.8%) to the B-Victoria lineage.
The WHO Consultation and Information Meeting on the Composition of Influenza Virus Vaccines for use in the 2019-2020 Northern Hemisphere Influenza Season was held on 18-21 February 2019 in Beijing, China. It was recommended that egg based quadrivalent vaccines contain the following:
- an A/Brisbane/02/2018 (H1N1)pdm09 - like virus;
- an A(H3N2) virus to be announced on 21 March 2019*;
- a B/Colorado/06/2017- like virus (B/Victoria/2/87 lineage);
- and a B/Phuket/3073/2013 - like virus (B/Yamagata/16/88 lineage).
It was also recommended that the influenza B virus component of trivalent vaccines for use in the 2019-2020 northern hemisphere influenza season be a B/Colorado/06/2017-like virus of the B/Victoria/2/87-lineage.
* In light of recent changes in the proportions of genetically and antigenically diverse A(H3N2) viruses, the recommendation for the A(H3N2) component has been postponed.
Link to vaccine recommendation
Detailed influenza update
Download PDF
pdf, 815kb
Unlike the relatively stable H1N1 virus - which emerged only a decade ago - the H3N2 virus has been circulating now for more than a half century. Over that time it has had to reinvent itself innumerable times (via antigenic drift) to evade acquired immunity, resulting in an increasing number of subclades of the virus co-circulating around the globe.
All of which has made the decision of which H3N2 vaccine component to recommend - which must be made 6 months in before the next flu season - increasingly difficult.Given the estimated toll of the last year's severe H3N2 season (see CDC: More Than 900,000 Hospitalizations & 80,000 Deaths In Last Winter's Flu Season), this is a decision well worth delaying a month if it increases the chances of getting it right.
