Twice each year influenza experts gather to discuss recent developments in human and animal influenza viruses around the world, and to decide on the composition of the next influenza season’s flu vaccine.
NIAID has a terrific 3-minute video that shows how influenza viruses drift over time, and why the flu shot must be frequently updated, which you can view at this link.
Due to the time it takes to manufacture and distribute a vaccine, decisions on which strains to include must be made at least six months in advance, which means the composition of next year's Southern Hemisphere’s vaccine must be decided upon in late September.As we've discussed often (see The Enigmatic, Problematic H3N2 Influenza Virus), coming up with a good vaccine match for seasonal H3N2 has become increasingly more difficult in recent years.
Last winter we saw a modest level of protection (34%) against H3N2, according to the CDC's MMWR report of June 30th.
Data collected through the U.S. Influenza Vaccine Effectiveness Network during November 28, 2016–April 14, 2017, indicate that influenza vaccination this season reduced the overall risk for influenza-associated medical visits by 42% (95% CI = 35%–48%).
Vaccine effectiveness against the predominant influenza A(H3N2) viruses was 34% (95% CI = 24%–42%) and vaccine effectiveness against influenza B viruses was 56% (95% CI = 47%–64%).
Earlier this week, we saw comments from Australia's Chief Medical Officer (see Australian CMO Statement On Flu Vaccine Effectiveness) placing some of the blame for their unusually rough flu season on `. . . the effectiveness of the vaccines has been less than usual this year, particularly in terms of protecting the elderly against influenza A (H3N2).'
This week the World Health Organization brought together representatives from GISRS (Global Influenza Surveillance and Response System), along with members of OFFLU (the OIE/FAO Network on Animal Influenza), and other experts to recommend what flu strains to include in next year's Southern Hemisphere flu vaccine.
Today, they've released their recommendations, which includes a new H3N2 vaccine component (A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus) which includes some of the changes we've seen in the virus (including the AA substitution N121K in the HA gene) over the past 8 months, and a switch from the Victoria Lineage B virus back to a Yamagata lineage virus for a trivalent vaccine.
Recommended composition of influenza virus vaccines for use in the 2018 southern hemisphere influenza season
28 September 2017
It is recommended that trivalent vaccines for use in the 2018 southern hemisphere influenza season contain the following:
It is recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Brisbane/60/2008-like virus.
- an A/Michigan/45/2015 (H1N1)pdm09-like virus;
- an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus; and
- a B/Phuket/3073/2013-like virus.
For more information
Recommended composition of influenza virus vaccines for use in the 2018 southern hemisphere influenza season - full report
There are many theories over why flu vaccines aren't as effective as we'd like, ranging from antigenic drift, to vaccine strain selection, to mutations that can occur in the (primarily egg-based) manufacturing process.
You'll find an excellent review in last week's Science Magazine article called:
While the flu vaccine can’t promise anything close to 100% protection, it – along with practicing good flu hygiene (washing hands, covering coughs, & staying home if sick) – still remains your best strategy for avoiding the flu and staying healthy this winter.
Even assuming this year's shot only provides modest protection, if an unusually severe H3N2 season materializes this winter, you'll probably want every advantage you can get.