Photo Credit - CDC PHIL
#13,809
Over the past two flu seasons - which have been H3N2-dominated years in North America - we've seen some pretty disappointing Vaccine Effectiveness (VE) numbers (see last February's Early Season Flu Surveillance & Vaccine Effectiveness (VE) - Canada), suggesting the vaccine was barely 20% effective against that subtype.
In 2017's The Enigmatic, Problematic H3N2 Influenza Virus we looked at a the growing genetic diversity within the H3 subtype, and in PNAS: Egg-Passaged Flu Vaccine Antibodies Poorly Neutralize Recent H3N2 Viruses we looked at some of the challenges in producing an H3 flu vaccine using traditional methods.While the vaccine's poor performance seems to have come from the confluence of several factors - at the same time its VE against H1N1 and influenza B viruses have remained reasonably good. Often in the 50%-70% range.
Today Eurosurveillance has published the latest VE estimates out of Canada - which started their flu season a month before the United States - and it finds this year the flu vaccine is roughly 70% effective against the predominant H1N1 subtype.
There apparently isn't enough data to generate estimates on the vaccine's VE against the minority players this season; H3N2 and Influenza B. Presumably we'll get some data on that in the spring.This is a lengthy detailed study, and I've only posted a few excerpts. Follow the link to read it in its entirety.
Interim estimates of 2018/19 vaccine effectiveness against influenza A(H1N1)pdm09, Canada, January 2019
Danuta M Skowronski1,2, Siobhan Leir1, Suzana Sabaiduc1, Michelle Murti3,4, James A Dickinson5, Romy Olsha3, Jonathan B Gubbay3,4, Matthew A Croxen6,7, Hugues Charest8, Tracy Chan1, Nathalie Bastien9, Yan Li9, Mel Krajden1,2, Gaston De Serres8,10,11(SNIP)
The 2018/19 influenza season in Canada for the period spanning November through January has been characterised by dominant influenza A(H1N1)pdm09 activity, with lesser influenza A(H3N2) and little influenza B contribution [1]. This profile is in contrast to the 2017/18 season which was comprised of dominant influenza A(H3N2) and early influenza B(Yamagata) co-circulation [2]. The last influenza A(H1N1)pdm09-dominant epidemics in Canada were in 2013/14 and 2015/16 [3,4].
The 2018/19 influenza vaccine for the northern hemisphere contains an A/Michigan/45/2015 (H1N1)pdm09-like antigen (belonging to clade 6B.1). The same component was included in the 2017/18 northern and the 2018 southern hemisphere vaccines [5]. Preliminary estimates of vaccine effectiveness (VE) from Australia’s 2018 season showed substantial VE of 78% (95% confidence interval (CI): 51 to 91) against influenza A(H1N1)pdm09 viruses [6]. Here we present interim 2018/19 VE estimates against influenza A(H1N1)pdm09 viruses from the Canadian Sentinel Practitioner Surveillance Network (SPSN), including detailed genetic characterisation of contributing viruses.
DISCUSSION
In this interim analysis, the 2018/19 influenza vaccine is estimated to have reduced the risk of medically attended influenza A(H1N1)pdm09 illness in Canada by 72%. This 2018/19 mid-season VE estimate against dominant influenza A(H1N1)pdm09 viruses is substantially higher than last reported in the mid-season analysis from Canada for the 2017/18 A(H3N2)-dominant influenza epidemic, for which VE against A(H3N2) viruses was below 20% (with a paucity of A(H1N1)pdm09 cases detected) [2].
Our 2018/19 VE estimate of 72% (95% CI: 60 to 81) against influenza A(H1N1)pdm09 viruses is comparable to a preliminary report from Australia using the same vaccine component for their 2018 season (78%) [6]. Both estimates are higher than reported in prior meta-analysis for influenza A(H1N1)pdm09 viruses (61%; 95% CI: 57 to 65) [12]. The Canadian SPSN estimate for 2018/19 is similar to mid-season estimates from our network during the last two A(H1N1)pdm09-dominant epidemics in 2013/14 and 2015/16 [3,4]. Of note, the 2013/14 epidemic peaked in January 2014, with comparable VE estimates at mid- and end-of-season analysis (74%; 95% CI: 58 to 83 and 71%; 95% CI: 58 to 80, respectively) [10]. Conversely, the mid-season VE estimate for 2015/16 was substantially higher than the end-of-season estimate (64%; 95% CI: 44 to 77 vs 43%; 95% CI: 25 to 57), a finding that may in part be explained by waning of immunity and the unusually delayed epidemic peak in March 2016 (after which half the cases were accrued) [13]. Similar to 2013/14, the current season’s epidemic may have already peaked nationally in Canada; however, there is regional variation in the timing and intensity of activity [1]. Differences in VE estimates at end-of-season analysis cannot be ruled out.
(SNIP)
While the season in Canada commenced earlier than in recent years [1], notable influenza activity in the US and most of Europe was not observed until mid-December [14,15]. Further, while influenza A(H3N2) has accounted for less than 10% of subtyped A viruses in this study and nationally in Canada [1], influenza A(H3N2) has predominated in south-eastern regions in the US, and co-circulation has been observed in Europe, with influenza A(H3N2) accounting for about one third of subtyped influenza A detections [14,15]. It remains to be seen how varying virological and participant profiles will impact VE estimates elsewhere across the northern hemisphere.
Interim estimates from Canada for the 2018/19 northern hemisphere indicate substantial VE of ca 70% against influenza A(H1N1)pdm09. Thus far, this epidemic has taken a greater toll on children younger than 9 years even when compared with previous A(H1N1)pdm09-dominant seasons. Given ongoing epidemic activity in some regions, vaccination should be advocated to minimise the A(H1N1)pdm09-associated disease burden. In the context of observed genetic diversity, monitoring for further evolution in circulating 6B.1 variants, and potential impact on vaccine protection, is warranted.
