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Eurosurveillance, Volume 21, Issue 4, 28 January 2016
Rapid communication
Barr, Vijaykrishna, and Sullivan: Differential age susceptibility to influenza B/Victoria lineage viruses in the 2015 Australian influenza season

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Citation style for this article: Barr IG, Vijaykrishna D, Sullivan SG. Differential age susceptibility to influenza B/Victoria lineage viruses in the 2015 Australian influenza season. Euro Surveill. 2016;21(4):pii=30118. DOI: http://dx.doi.org/10.2807/1560-7917.ES.2016.21.4.30118

Received:13 January 2016; Accepted:26 January 2016


The 2015 season was notable for the predominance of influenza B in Australia. According to the Australian Influenza Surveillance Report [1] for the period 1 January to 9 October, 61% of cases were typed as influenza B and 38% influenza A (29% A (not subtyped), 7% A(H3N2) and 2% A(H1N1)pdm09). That season was also interesting due to the waxing and waning of the two B lineages over the season. Here, we summarise the lineage distribution using viruses submitted to the WHO Collaborating Centre for Reference and Research on Influenza in Melbourne for 2015 and compared these data with data from 2008, the last year when influenza B viruses predominated in Australia.

The 2015 influenza season in Australia

Lineage data was available for 816 influenza B viruses from 2008 and 1,648 from 2015 that were received by the Centre from all over Australia. The formal representativeness of these samples is unknown. Generally there is a bias towards sampling from children and this is seen in most years in most general and sentinel surveillance systems and was also seen in the 2008 [2] and 2015 [1] Australian influenza seasons. It is unlikely that any bias would exist in selecting patients with a particular B lineage, and given the size and the geographical diversity of the samples tested, it is likely these data will provide an accurate estimate of the overall situation with influenza B in Australia during these two years. During the 2015 pre-season period (January–April) and the early part of the influenza season (May–June), B/Yamagata/16/88 lineage (B/Yam) viruses predominated. However, from July to November, B/Victoria/2/87 lineage (B/Vic) viruses increased rapidly and were dominant from August (Figure 1). Notably, this same switch was seen during the 2008 season with similar timing although almost no B/Vic lineage viruses were detected in Australia before June (Figure 1). The distributions of lineages during 2015 were similar when individual Australian states were examined, with the exception of the Northern Territory, which has a small population largely situated in the tropics, that had an almost total B/Vic year (36/39 B viruses). Australia’s most populous state, New South Wales, experienced an increase in the proportion of B/Vic viruses from low levels early in 2015 to 28% during the period from 15 June to 12 July 2015 [3] which according to our study continued to increase over the rest of the influenza season, and B/Vic viruses predominated from July onwards. Children and young adults carry a higher burden of influenza B disease than older adults and the elderly. According to the Australian Paediatric Surveillance Unit 2015 saw 88 children 15 years and younger (median: 3.3 years) hospitalised with severe complications of influenza between 1 July 2015 and 30 September 2015. Roughly two thirds (n = 59) were influenza B cases (lineage unknown) [1]. Overall, the average duration of hospitalisation was four days, 20 required an ICU admission, and there were three influenza-associated deaths, all associated with influenza B infections [1].

Figure 1

Relative frequency of influenza B subtypes received by month of specimen collection, Australia, 2008 (n = 816) and 2015 (n = 1,648)

/images/dynamic/articles/21362/16-00035-f1

B/Vic: B/Victoria/2/87 lineage; B/Yam: B/Yamagata/16/88 lineage.

Numbers at the bottom of the figure are the total number of B viruses tested for each month. Top panel: influenza B subtypes in 2008 (n = 415 B/Vic, n = 401 B/Yam); bottom panel: influenza B subtypes in 2015 (n = 852 B/Vic, n = 796 B/Yam).

Antigenic and genetic drift

The move in dominance by the B/Vic viruses in 2015 was not accompanied by any major antigenic changes from the B/Vic viruses that circulated in smaller numbers in 2014. All Australian B/Vic viruses analysed by the Centre were antigenically B/Brisbane/60/2008-like as they were in 2014 (data not shown). Equally, the 2015 B/Yam viruses that were analysed remained antigenically B/Phuket3073/2013-like, similar to B/Yam viruses that circulated in Australia from mid-2014 (data not shown). However, subtle phylogenetic differences in the haemagglutinin (HA) genes of the two B lineages were apparent (Figure 2). The HA gene phylogeny revealed a greater diversity for B/Yam viruses isolated in Australia during 2015 (n = 56) than during 2014 (n = 42) (Figure 2, top panel). The mean time to most recent common ancestor (mTMRCA) extended beyond 2012 and the isolates belonged to three antigenic types (B/Wisconsin/1/2010, B/Massachusetts/2/2012 and B/Phuket/3073/2013), although the majority from 2015 (52 of the 56 viruses from 2015) belonged to the B/Phuket/3073/2013 clade (also known as group 3) with a mTMRCA in mid-2014. Reconstruction of non-synonymous changes along this phylogeny revealed an amino acid substitution (M267V) in the subclade of B/Phuket/3073/2013-like viruses that were dominant during the 2015 season, suggesting that this mutation may have contributed to increased viral fitness. All Australian B/Vic viruses from 2015 (n = 54) were phylogenetically B/Brisbane/60/2008-like (also referred to as clade 1A) with an mTMRCA in 2013. This clade was made up of three distinct subclades (Figure 2, bottom panel) the largest of which had the non-synonymous amino acid substitutions V161I and I132V that may have also enhanced the fitness of these viruses.

Figure 2

Maximum clade credibility trees showing the evolution of haemagglutinin genes of sequenced Australian influenza B viruses from 2014 and 2015 (n = 168)

/images/dynamic/articles/21362/16-00035-f2

Phylogenies were inferred using a relaxed molecular clock model in a Bayesian Markov Chain Monte Carlo framework with the programme BEASTv1.8 [15].

Panel A: B/Yamagata/16/88 lineage viruses isolated in Australia in 2014 (n = 42) and 2015 (n = 56); Panel B: B/Victoria/2/87 lineage viruses isolated in Australia in 2014 (n = 16) and 2015 (n = 54). Red bars: Australian influenza B viruses from 2015; black bars: Australian influenza B viruses from 2014. Non-synonymous amino acid changes that occurred during the evolution of the lineages are shown adjacent to the nodes. All available haemagglutinin (HA) sequences were obtained from The Global Initiative on Sharing All Influenza Data (GISAID; http://platform.gisaid.org/epi3/frontend). See the Table at the end of the article for details of the source and details of the virus and the sequencing laboratory.

Age distribution of influenza B infections

The age distribution of patients with confirmed B/Vic infections in 2015 was positively skewed, with a greater number of infections among the younger age groups (mean:  26.4 years, median: 19.9 years). For B/Yam infections, the age distribution was more even (mean: 42.4 years, median: 43.8 years; p < 0.001 for Wilcoxon rank sum test). This age differential was less evident in 2008 where, despite the high proportion of viruses obtained from children younger than five years, the interquartile range indicated that B/Yam viruses affected a broader age range than the B/Vic viruses (Figure 3). This age difference between lineages has previously been reported from a household study in Hong Kong [4]. There, children younger than 15 years had a 13-fold increased risk of secondary influenza infection with a B/Vic virus than with a B/Yam virus, during a period when both lineages were co-circulating. Similar findings were reported in population studies in southern China during the 2009 and 2010 seasons [5], over three seasons in Slovenia (2010–13 [6]) and in our earlier studies from eastern Australia and New Zealand, where major differences in lineage distribution were observed in subjects older than five years [5,7].

Figure 3

Age distribution of confirmed influenza B cases by lineage, Australia, 2008 (n = 780) and 2015 (n = 1,638)

/images/dynamic/articles/21362/16-00035-f3

IQR: interquartile range; SD: standard deviation.

Data shown are samples for which age data was available. Bars show the histogram in one-year age increments by lineage. The shaded areas indicate the smoothed density estimate of the age distribution. Values provided on the graphs for each lineage are mean (SD) or median (IQR). P values are for the t-test comparing mean age between the two lineages and the Wilcoxon rank-sum test for comparing medians.

Discussion

A predominance of influenza B viruses in an influenza season occurs infrequently, usually in the order of once every 10 years. Prior to 2015, it last occurred in Australia in the 2008 season, where 54% of typed viruses were influenza B, 43% were influenza A and 3% untyped [2]. Similarly in Europe for the seasons from 2001/02 to 2010/11, influenza B was the majority influenza type (59.1%) in only one season (2005/06). In the United States (US) over the same period, 2002/03 was the season with the highest proportion of influenza B (42.6%) among of all typed viruses [8]. The two antigenic and genetically distinct lineages of influenza B viruses (B/Yam and B/Vic) have co-circulated in various proportions since 2002 in most countries. Trivalent influenza vaccines (containing only one B virus lineage) used over this time have tried to match these changing lineage circulation patterns. Because of a number of poor matches during the 2000s, quadrivalent vaccines (containing viruses from both B lineages) were developed and have recently been introduced in order to improve vaccine effectiveness. The 2015 influenza vaccines licensed in Australia were all traditional inactivated virus vaccines (live attenuated influenza vaccines and recombinant vaccines were not available) with mostly trivalent vaccine containing only the B/Yam component being used along with low levels of quadrivalent vaccine.

The reasons for the apparent differential age susceptibility between the two B lineages described in this study are unknown. It is, however, well known that the different influenza types/subtypes do affect different age profiles; both seasonal and 2009 pandemic A(H1N1) as well as influenza B viruses infect a younger population than A(H3N2) viruses [9], although in recent years, the median age of influenza A(H1N1)pdm09 cases has been increasing [6,10], again for unknown reasons. Studies to date have not shown differences in clinical presentation for the different B lineages [4,5], but long-term data on hospitalisations and deaths are lacking. In a study by Paddock et al. on deaths attributed to confirmed influenza B in the US from 2000 to 2010, the majority of subjects were  18 years and younger (34/45 cases), and a slightly higher proportion of infections were B/Vic compared with B/Yam (25 vs 17 deaths, respectively, in those cases that could be characterised) [11]. More studies are required to determine if there is indeed any difference in outcomes following severe infections with either of the B lineages in different age groups.

It is probable that the prior exposure history of the different age groups has influenced our observations. However, this is difficult to deduce from the present data. For example, five-year-old Australian children in 2015 were likely to have been exposed to a mixture of B/Yam viruses, which circulated in 2013 and 2014, and B/Vic viruses, which circulated from 2009 to 2012, as was the case in for five-year-olds in 2008. Possible exposure therefore fails to explain the elevated proportion of five year-old children infected with B/Yam viruses in 2008 or with B/Vic in 2015. In addition, it is unlikely given the low levels of childhood vaccination in Australia that this this would have significantly altered the circulation patterns of the influenza B lineages. Vaccination uptake is generally below 10% among Australian children [12]. Childhood influenza vaccination is only recommended for children of aboriginal descent five years and younger and for children six months and older with comorbidities [13].

We have suggested previously that there may be some fundamental differences in the receptor specificity of the different influenza B lineages and that the distribution or density of receptors for influenza B viruses in the respiratory tract of humans may differ with age [7]. Others have shown differential responses of children to B/Yam and B/Vic antigens contained in influenza vaccines that might also contribute to differential susceptibility to these two lineages 14]. Further work is needed to fully understand the basis of these observations and to determine if the differences are due to receptor variation or density during ageing or prior exposure history or a mixture of both. If indeed young children are at an elevated risk of infection with B/Vic viruses, then it may be prudent to prioritise distribution of quadrivalent vaccines (containing viruses from both B lineages) to this age group. This is relevant to the current northern hemisphere influenza season where the trivalent vaccine contains a B/Yam lineage virus, but B/Vic lineage viruses are in our view likely to increase substantially during the current season. Use of the quadrivalent vaccine for this subgroup (or preferably for the whole population) would be potentially advantageous in improving influenza vaccine effectiveness.

Table

Australian influenza B viruses and haemagglutinin gene sequences used to construct Figure 2, obtained from The Global Initiative on Sharing All Influenza Data (GISAID)a


Segment ID Collection date Isolate name Influenza B lineage Originating laboratory Authorsb
EPI551283 2014-Aug-11 B/Newcastle/21/2014 Victoria John Hunter Hospital A
EPI561891 2014-Dec-05 B/Darwin/43/2014 Victoria Royal Darwin Hospital A
EPI541294 2014-Feb-18 B/Tasmania/1/2014 Victoria Royal Hobart Hospital A
EPI541365 2014-Feb-21 B/Perth/503/2014 Victoria Pathwest A
EPI529392 2014-Jan-20 B/Brisbane/3/2014 Victoria QHSS A
EPI540771 2014-Jan-20 B/Perth/501/2014 Victoria Pathwest A
EPI551321 2014-Jul-02 B/South Australia/20/2014 Victoria IMVS A
EPI540747 2014-Mar-29 B/Brisbane/12/2014 Victoria QHSS A
EPI551327 2014-May-03 B/Sydney/19/2014 Victoria Clinical Virology Unit, CDIM A
EPI541291 2014-May-06 B/Brisbane/13/2014 Victoria QHSS A
EPI562018 2014-Nov-14 B/Brisbane/71/2014 Victoria QHSS A
EPI561888 2014-Nov-20 B/Brisbane/74/2014 Victoria QHSS A
EPI561873 2014-Oct-09 B/Brisbane/62/2014 Victoria QHSS A
EPI561876 2014-Oct-10 B/Brisbane/63/2014 Victoria QHSS A
EPI561924 2014-Oct-15 B/Victoria/7/2014 Victoria VIDRL A
EPI551336 2014-Sep-09 B/Victoria/204/2014 Victoria Royal Chidrens Hospital A
EPI636426 2015-Apr-23 B/Darwin/9/2015 Victoria Royal Darwin Hospital B
EPI636340 2015-Apr-28 B/Brisbane/46/2015 Victoria QHSS B
EPI636409 2015-Apr-30 B/Darwin/11/2015 Victoria Royal Darwin Hospital B
EPI675691 2015-Aug-02 B/Victoria/849/2015 Victoria Austin Health B
EPI675652 2015-Aug-03 B/South Australia/1036/2015 Victoria IMVS B
EPI648854 2015-Aug-03 B/Victoria/847/2015 Victoria Austin Health B
EPI675636 2015-Aug-04 B/Newcastle/1012/2015 Victoria IMVS B
EPI675677 2015-Aug-05 B/Victoria/1009/2015 Victoria IMVS B
EPI675663 2015-Aug-09 B/Sydney/137/2015 Victoria Westmead Hospital B
EPI648856 2015-Aug-11 B/Victoria/861/2015 Victoria Austin Health B
EPI675694 2015-Aug-18 B/Victoria/898/2015 Victoria Austin Health B
EPI675672 2015-Aug-20 B/Tasmania/30/2015 Victoria Royal Hobart Hospital B
EPI675646 2015-Aug-30 B/Perth/201/2015 Victoria Pathwest B
EPI630025 2015-Feb-05 B/Brisbane/4/2015 Victoria QHSS A
EPI630050 2015-Feb-12 B/South Australia/3/2015 Victoria IMVS A
EPI636504 2015-Jul-02 B/South Australia/1015/2015 Victoria IMVS B
EPI648850 2015-Jul-06 B/Townsville/7/2015 Victoria QHSS B
EPI636421 2015-Jul-07 B/Darwin/17/2015 Victoria Royal Darwin Hospital B
EPI648882 2015-Jul-12 B/Victoria/524/2015 Victoria Monash Medical Centre B
EPI636621 2015-Jul-12 B/Victoria/525/2015 Victoria Monash Medical Centre B
EPI675604 2015-Jul-13 B/Brisbane/186/2015 Victoria QHSS B
EPI648868 2015-Jul-13 B/Canberra/27/2015 Victoria Canberra Hospital B
EPI648846 2015-Jul-14 B/Brisbane/185/2015 Victoria QHSS B
EPI675639 2015-Jul-15 B/Newcastle/28/2015 Victoria John Hunter Hospital B
EPI648870 2015-Jul-19 B/Canberra/29/2015 Victoria Canberra Hospital B
EPI636388 2015-Jul-19 B/Canberra/30/2015 Victoria Canberra Hospital B
EPI648848 2015-Jul-30 B/Darwin/22/2015 Victoria Royal Darwin Hospital B
EPI675688 2015-Jul-31 B/Victoria/843/2015 Victoria Austin Health B
EPI636549 2015-Jun-01 B/Sydney/11/2015 Victoria Clinical Virology Unit, CDIM B
EPI636525 2015-Jun-04 B/South Australia/49/2015 Victoria IMVS B
EPI636567 2015-Jun-15 B/Tasmania/2/2015 Victoria Royal Hobart Hospital B
EPI636329 2015-Jun-27 B/Brisbane/136/2015 Victoria QHSS B
EPI636415 2015-Jun-28 B/Darwin/14/2015 Victoria Royal Darwin Hospital B
EPI636635 2015-Jun-28 B/Victoria/557/2015 Victoria Monash Medical Centre B
EPI636577 2015-Jun-29 B/Tasmania/5/2015 Victoria Royal Hobart Hospital B
EPI636465 2015-Jun-30 B/Newcastle/1005/2015 Victoria IMVS B
EPI636560 2015-Mar-02 B/Sydney/503/2015 Victoria Prince of Wales Hospital B
EPI636334 2015-Mar-16 B/Brisbane/15/2015 Victoria QHSS B
EPI636584 2015-Mar-31 B/Townsville/3/2015 Victoria QHSS B
EPI636605 2015-Mar-31 B/Victoria/502/2015 Victoria Monash Medical Centre B
EPI636354 2015-May-08 B/Brisbane/55/2015 Victoria QHSS B
EPI636361 2015-May-21 B/Brisbane/69/2015 Victoria QHSS B
EPI636363 2015-May-24 B/Brisbane/70/2015 Victoria QHSS B
EPI636369 2015-May-25 B/Brisbane/73/2015 Victoria QHSS B
EPI636485 2015-May-28 B/Perth/24/2015 Victoria Pathwest B
EPI636488 2015-May-28 B/Perth/25/2015 Victoria Pathwest B
EPI636658 2015-May-30 B/South Australia/48/2015 Victoria IMVS B
EPI636472 2015-May-31 B/Newcastle/7/2015 Victoria John Hunter Hospital B
EPI675619 2015-Oct-03 B/Darwin/65/2015 Victoria Royal Darwin Hospital B
EPI675622 2015-Oct-09 B/Darwin/70/2015 Victoria Royal Darwin Hospital B
EPI675660 2015-Sep-07 B/Sydney/1071/2015 Victoria IMVS B
EPI675655 2015-Sep-11 B/South Australia/118/2015 Victoria IMVS B
EPI675602 2015-Sep-16 B/Brisbane/1036/2015 Victoria IMVS B
EPI675686 2015-Sep-25 B/Victoria/700/2015 Victoria Monash Medical Centre B
EPI540782 2014-Apr-04 B/Newcastle/3/2014 Yamagata John Hunter Hospital A
EPI540744 2014-Apr-08 B/Darwin/35/2014 Yamagata Royal Darwin Hospital A
EPI540765 2014-Apr-15 B/Sydney/8/2014 Yamagata Prince of Wales Hospital A
EPI540762 2014-Apr-29 B/Sydney/7/2014 Yamagata Prince of Wales Hospital A
EPI551286 2014-Aug-11 B/Newcastle/22/2014 Yamagata John Hunter Hospital A
EPI551289 2014-Aug-12 B/Newcastle/25/2014 Yamagata John Hunter Hospital A
EPI561915 2014-Dec-02 B/Sydney/39/2014 Yamagata Westmead Hospital A
EPI562030 2014-Dec-03 B/Perth/579/2014 Yamagata Pathwest A
EPI529622 2014-Feb-17 B/Townsville/3/2014 Yamagata QHSS A
EPI540779 2014-Feb-25 B/Perth/505/2014 Yamagata Pathwest A
EPI529377 2014-Jan-12 B/Darwin/4/2014 Yamagata Royal Darwin Hospital A
EPI529619 2014-Jan-28 B/Brisbane/4/2014 Yamagata QHSS A
EPI551274 2014-Jul-03 B/Newcastle/12/2014 Yamagata John Hunter Hospital A
EPI540912 2014-Jul-03 B/South Australia/21/2014 Yamagata IMVS A
EPI551280 2014-Jul-24 B/Newcastle/19/2014 Yamagata John Hunter Hospital A
EPI551324 2014-Jul-31 B/Sydney/1002/2014 Yamagata IMVS A
EPI541331 2014-Jun-02 B/Brisbane/22/2014 Yamagata QHSS A
EPI541279 2014-Jun-12 B/South Australia/16/2014 Yamagata IMVS A
EPI541338 2014-Jun-13 B/Newcastle/8/2014 Yamagata John Hunter Hospital A
EPI551277 2014-Jun-17 B/Newcastle/17/2014 Yamagata John Hunter Hospital A
EPI540909 2014-Jun-30 B/South Australia/1002/2014 Yamagata IMVS A
EPI541241 2014-Mar-07 B/Brisbane/8/2014 Yamagata QHSS A
EPI551249 2014-Mar-24 B/Brisbane/9/2014 Yamagata QHSS A
EPI540759 2014-Mar-26 B/Sydney/5/2014 Yamagata Prince of Wales Hospital A
EPI540785 2014-Mar-28 B/Newcastle/5/2014 Yamagata John Hunter Hospital A
EPI540906 2014-May-05 B/Sydney/13/2014 Yamagata Westmead Hospital A
EPI540768 2014-May-06 B/Sydney/9/2014 Yamagata Prince of Wales Hospital A
EPI540753 2014-May-14 B/South Australia/5/2014 Yamagata IMVS A
EPI540756 2014-May-17 B/South Australia/7/2014 Yamagata IMVS A
EPI541288 2014-May-27 B/South Australia/1000/2014 Yamagata IMVS A
EPI561918 2014-Nov-06 B/Victoria/512/2014 Yamagata Monash Medical Centre A
EPI561885 2014-Nov-11 B/Brisbane/70/2014 Yamagata QHSS A
EPI630034 2014-Nov-14 B/Canberra/20/2014 Yamagata Canberra Hospital A
EPI561870 2014-Oct-08 B/Brisbane/61/2014 Yamagata QHSS A
EPI561912 2014-Oct-08 B/Perth/569/2014 Yamagata Pathwest A
EPI561879 2014-Oct-20 B/Brisbane/65/2014 Yamagata QHSS A
EPI561882 2014-Oct-27 B/Brisbane/66/2014 Yamagata QHSS A
EPI561921 2014-Oct-30 B/Victoria/6/2014 Yamagata VIDRL A
EPI551820 2014-Sep-02 B/Victoria/804/2014 Yamagata Austin Health A
EPI551330 2014-Sep-08 B/Townsville/1000/2014 Yamagata IMVS A
EPI551264 2014-Sep-09 B/Darwin/38/2014 Yamagata Royal Darwin Hospital A
EPI551333 2014-Sep-09 B/Victoria/202/2014 Yamagata Royal Chidrens Hospital A
EPI636392 2015-Apr-02 B/Canberra/4/2015 Yamagata Canberra Hospital B
EPI636341 2015-Apr-03 B/Brisbane/33/2015 Yamagata QHSS B
EPI630067 2015-Apr-05 B/Victoria/500/2015 Yamagata Monash Medical Centre A
EPI636553 2015-Apr-09 B/Sydney/5/2015 Yamagata Clinical Virology Unit, CDIM B
EPI642630 2015-Apr-14 B/Brisbane/47/2015 Yamagata WHO CC NA
EPI636506 2015-Apr-23 B/South Australia/12/2015 Yamagata IMVS B
EPI636606 2015-Apr-25 B/Victoria/503/2015 Yamagata Monash Medical Centre B
EPI648860 2015-Apr-25 B/Victoria/530/2015 Yamagata Monash Medical Centre B
EPI636345 2015-Apr-28 B/Brisbane/50/2015 Yamagata QHSS B
EPI648852 2015-Aug-01 B/Victoria/845/2015 Yamagata Austin Health B
EPI675669 2015-Aug-02 B/Sydney/70/2015 Yamagata Westmead Hospital B
EPI675644 2015-Aug-03 B/Perth/166/2015 Yamagata Pathwest B
EPI675657 2015-Aug-04 B/Sydney/1031/2015 Yamagata IMVS B
EPI675666 2015-Aug-13 B/Sydney/153/2015 Yamagata Westmead Hospital B
EPI675675 2015-Aug-21 B/Tasmania/32/2015 Yamagata Royal Hobart Hospital B
EPI630031 2015-Feb-03 B/Canberra/1/2015 Yamagata Canberra Hospital A
EPI630047 2015-Feb-10 B/South Australia/2/2015 Yamagata IMVS C
EPI630053 2015-Feb-21 B/South Australia/4/2015 Yamagata IMVS A
EPI630055 2015-Feb-23 B/South Australia/5/2015 Yamagata IMVS C
EPI630064 2015-Feb-26 B/Townsville/1/2015 Yamagata QHSS A
EPI630016 2015-Jan-04 B/Brisbane/1/2015 Yamagata QHSS A
EPI630061 2015-Jan-28 B/Sydney/2/2015 Yamagata Clinical Virology Unit, CDIM A
EPI630058 2015-Jan-30 B/Sydney/1000/2015 Yamagata IMVS A
EPI636636 2015-Jul-07 B/Victoria/543/2015 Yamagata Monash Medical Centre B
EPI636618 2015-Jul-09 B/Victoria/519/2015 Yamagata Monash Medical Centre B
EPI636601 2015-Jul-13 B/Victoria/32/2015 Yamagata VIDRL B
EPI636387 2015-Jul-14 B/Canberra/28/2015 Yamagata Canberra Hospital B
EPI636627 2015-Jul-14 B/Victoria/532/2015 Yamagata Monash Medical Centre B
EPI636641 2015-Jul-21 B/Victoria/952/2015 Yamagata Royal Chidrens Hospital B
EPI675641 2015-Jul-29 B/Perth/136/2015 Yamagata Pathwest B
EPI636592 2015-Jun-01 B/Victoria/301/2015 Yamagata Melbourne Pathology B
EPI636531 2015-Jun-06 B/South Australia/50/2015 Yamagata IMVS B
EPI636566 2015-Jun-06 B/Tasmania/1/2015 Yamagata Royal Hobart Hospital B
EPI636313 2015-Jun-14 B/Brisbane/100/2015 Yamagata QHSS B
EPI636322 2015-Jun-18 B/Brisbane/118/2015 Yamagata QHSS B
EPI636460 2015-Jun-22 B/Newcastle/1003/2015 Yamagata IMVS B
EPI636468 2015-Jun-22 B/Newcastle/20/2015 Yamagata John Hunter Hospital B
EPI636326 2015-Jun-25 B/Brisbane/132/2015 Yamagata QHSS B
EPI636379 2015-Jun-25 B/Canberra/13/2015 Yamagata Canberra Hospital B
EPI636535 2015-Jun-25 B/South Australia/71/2015 Yamagata IMVS B
EPI636574 2015-Jun-27 B/Tasmania/4/2015 Yamagata Royal Hobart Hospital B
EPI636383 2015-Jun-28 B/Canberra/15/2015 Yamagata Canberra Hospital B
EPI636541 2015-Jun-29 B/Sydney/1013/2015 Yamagata IMVS B
EPI630019 2015-Mar-02 B/Brisbane/11/2015 Yamagata QHSS A
EPI630022 2015-Mar-20 B/Brisbane/19/2015 Yamagata QHSS A
EPI636455 2015-May-03 B/Newcastle/1/2015 Yamagata John Hunter Hospital B
EPI636349 2015-May-04 B/Brisbane/54/2015 Yamagata QHSS B
EPI636515 2015-May-04 B/South Australia/22/2015 Yamagata IMVS B
EPI636514 2015-May-05 B/South Australia/18/2015 Yamagata IMVS B
EPI636500 2015-May-17 B/South Australia/1000/2015 Yamagata IMVS B
EPI636611 2015-May-17 B/Victoria/507/2015 Yamagata Monash Medical Centre B
EPI636482 2015-May-22 B/Perth/21/2015 Yamagata Pathwest B
EPI636521 2015-May-22 B/South Australia/28/2015 Yamagata IMVS B
EPI636593 2015-May-25 B/Townsville/6/2015 Yamagata QHSS B
EPI675616 2015-Sep-17 B/Darwin/61/2015 Yamagata Royal Darwin Hospital B
EPI675683 2015-Sep-24 B/Victoria/698/2015 Yamagata Monash Medical Centre B

IMVS: Institute of Medical and Veterinary Science; Pathwest: Pathwest QE II Medical Centre; QHSS: Queensland Health Scientific Services; VIDRL: Victoria Infectious Diseases Laboratory.

a All samples were sequenced and submitted by WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia, with the exception of B/Brisbane/47/2015 that was submitted by US Centers for Disease Control and Prevention.

bAuthors: A: Deng Y-M, Iannello P, Spirason N, Jelley L, Lau H, Komadina N; B: Deng Y-M, Iannello P, Spirason N, Lau H, Komadina N; C: Tilmanis D, Hurt A, Komadina N.


Acknowledgements

The Melbourne WHO Collaborating Centre for Reference and Research on Influenza is supported by the Australian Government Department of Health. The authors would like to thank all laboratories that supplied samples used in these studies, including the Australian WHO National Influenza Centres at VIDRL in Victoria, ICPMR in Sydney, Pathwest in Perth and other laboratories and hospitals in Australia. DV is supported by the Duke-NUS Signature Research Program funded by the Agency of Science, Technology and Research, Singapore and the Ministry of Health Singapore, and by contract HHSN272201400006C from the National Institute of Allergy and Infectious Disease, National Institutes of Health, Department of Health and Human Services, United States.

We acknowledge the authors, originating and submitting laboratories of the sequences from GISAID’s EpiFlu Database on which this research is based (see Table). All submitters of data may be contacted directly via the GISAID website www.gisaid.org

Conflict of interest

None declared.

Authors’ contributions

IB and SS wrote the manuscript, SS performed the epidemiological analysis, DV performed phylogenetic analyses, all authors revised the manuscript.


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