Tuesday, October 03, 2017

ECDC: H3N2 Flu Vaccine Component Likely `Suboptimal'


On the heels of the my last blog which featured a reassuring assessment from Hong Kong's CHP on the expected `match' of this year's flu vaccine to the H3N2 viruses in circulation - we get a diplomatically worded, but considerably less optimistic take from the ECDC - one which characterizes this year's H3N2 component as `sub-optimal'.
We've seen hints of this for several months (see here, here, here, and here) - although this year's Vaccine Effectiveness (VE) will ultimately depend upon the subclade of H3N2 that dominates this winter.  Something that could vary greatly around the world.
Last year's vaccine performance was - by most standards - disappointing.  Here in the United States, we only saw a modest level of protection (34%) against H3N2, according to the CDC's MMWR report of June 30th.

2016–17 Influenza Vaccine Effectiveness

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%).
This fall's northern hemisphere flu vaccine will use the same (A/Hong Kong/4801/2014-like) H3N2 virus as last year's formulation, but will add a new H1N1 strain. Although things could change, H3N2 appears poised to be the dominant subtype again this year.

Today's ECDC statement begins by summarizing last week's WHO announcement on changes to next year's flu vaccine for the Southern Hemisphere, then moves on to discuss this year's vaccine (bolding mine).

ECDC comment
World Health Organization, Geneva, Switzerland report, published 28 September 2017.
The World Health Organization (WHO) has recommended the composition of the trivalent influenza vaccine for the southern hemisphere winter 2018 influenza season as:
  • 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 (Yamagata lineage).
Quadrivalent vaccines, containing two influenza B viruses, should include the above three viruses and a B/Brisbane/60/2008-like virus (Victoria lineage).


ECDC Comment

WHO’s recommendations are based on knowledge of the viruses currently circulating worldwide. The recommendations were to change the A(H3N2) and B components of the trivalent influenza vaccines for the southern hemisphere vaccine.

The A/Michigan/45/2015 A(H1N1)pdm09 vaccine virus is close to the circulating A(H1N1)pdm09 viruses in its genetic and antigenic properties and should result in good vaccine effectiveness if A(H1N1)pdm09 viruses circulate widely. As A(H1N1)pdm09 did not circulate widely in the most recent 2016–2017 northern hemisphere influenza season, no vaccine effectiveness results are available for that subtype [2,3].

WHO has recommended changing the A(H3N2) virus component in the influenza vaccines for southern hemisphere 2018 influenza season to A/Singapore/INFIMH-16-0019/2016 which belongs to subclade 3C.2a1. Genetic analyses of circulating A(H3N2) showed that these viruses have undergone considerable genetic diversification of the HA gene from the current vaccine virus A/Hong Kong/4801/2014 (clade 3C.2a) [4]. Results for the 2016–2017 northern hemisphere influenza season, published mid-season, suggested 23–44% vaccine effectiveness against the recently circulating A(H3N2) viruses which were predominantly of clade 3C.2a [2,3]. 

The vaccine component for the 2016–2017 northern hemisphere season for A(H3N2) was A/Hong Kong/4801/2014 (clade 3C.2a). The vaccine strain for the upcoming winter season in the northern hemisphere remains the same and this does not correspond ideally with the A(H3N2) viruses currently circulating across the world [1]. Therefore, it is expected that the vaccine effectiveness against this subtype in the northern hemisphere 2017–2018 influenza season will be suboptimal, as anticipated by WHO [5], if the circulating strains resemble those circulating in the southern hemisphere. 

Globally, both B virus lineages continue to co-circulate, with B/Yamagata lineage being predominant [1]. WHO recommends the B/Yamagata lineage in the trivalent vaccine for the southern hemisphere 2018 influenza season. However, in the northern hemisphere, B/Brisbane/60/2008-like virus (Victoria lineage) is still included in the trivalent vaccine for the 2017–2018 influenza season. As the trivalent vaccine is the most widely used vaccine in the northern hemisphere, a suboptimal vaccine effectiveness against the B viruses is expected, if the B/Yamagata viruses continue to be predominant.
On the other hand, trivalent vaccines containing B/Victoria/2/87 lineage viruses may provide some cross-protection against B/Yamagata/16/88 lineage viruses [5]. A limited proportion of B/Victoria circulating viruses are antigenically different from the vaccine component. In the event that these viruses spread to the northern hemisphere during the season, a suboptimal vaccine effectiveness can be expected.

As all influenza (sub)types continued to co-circulate globally from February to September 2017, it is impossible to predict the proportions of circulating viruses next season and the expected protection using the recommended vaccine components. The technical difficulties in virus culture, characterisation and egg-propagation of influenza A(H3N2) viruses continue to make the selection of new vaccine components difficult.

(Continue . . . )

Note: Getting the quadrivalent vaccine, which is widely available in the United States, should help avoid the B/Yamagata - B/Victoria strain swap mentioned above for the trivalent vaccine.. 
While I've not been very optimistic about this year's H3N2 vaccine component for several months, I got the flu vaccine in September, figuring some protection during a potentially severe flu season beats having no protection at all.
While it may not be optimal - getting the vaccine – 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.

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