Eurosurveillance: B/Victoria Prevalence In Early New South Wales Flu Season

Photo Credit - CDC PHIL

 

#10,393

 

Because of the six months lead time required to produce and distribute a flu vaccine, twice each year the World Health Organization gathers together global influenza experts to decide on what stains to include in the next vaccine. Decisions on the vaccine being used right now in the Southern Hemisphere were made at the end of September 2014, while the Northern Hemisphere’s fall vaccine were decided upon last February.

 

It is always a little dicey trying to predict what flu strains will be dominate 6 to 12 months in the future, and last year we saw a big `mismatch’ with the H3N2 component  (see MMWR: Reduced Protection From This Year’s Flu Vaccine).

 

The formulation for both of those vaccines this year is identical, with (for the 6th year running) the 2009 H1H1 strain, a revamped H3N2 component, and a Yamagata lineage B/Phuket/3073/2013-like virus

 

Recommended composition of influenza virus vaccines for use in the 2015 southern hemisphere influenza season

25 September 2014

It is recommended that trivalent vaccines for use in the 2015 influenza season (southern hemisphere winter) contain the following:

• an A/California/7/2009 (H1N1)pdm09-like virus;
• an A/Switzerland/9715293/2013 (H3N2)-like virus^a;
• a B/Phuket/3073/2013-like virus.

It is recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Brisbane/60/2008-like virus.

 

In addition to picking which H1 and and H3 strain to include, experts must decide which of the two lineages of influenza B (Yamagata or Victoria) will dominate the next flu season. Influenza B often becomes the predominant strain late in the flu season, after influenza A has peaked, which puts even more time between the decision of what lineage to use, and its arrival. 

 

Over the first decade of the 21st century, the trivalent vaccine matched the dominant B strain only about 50% of the time. In 2012, the FDA approved the first Quadrivalent Flu vaccine, containing both Victoria and Yamagata lineage B strains (see Two B's Or Not Two B's? That Is the Question).

 

Being relatively stable, influenza B viruses don’t get as much respect as the highly mutable influenza A’s, even though they are quite capable of producing large epidemics with significant morbidity and mortality.  

This graphic from  CDC’s  2014-15 FluView shows Influenza B (green) dominating last spring.

 

With influenza activity in full swing in the Southern Hemisphere, we usually look at Australia and New Zealand around this time of year for clues as to what we might expect in the Northern Hemisphere this fall and winter.  

 

Yesterday Eurosurveillance published a Rapid Communications indicating that New South Wales (NSW) is reporting unusually heavy influenza B activity, and that a substantial portion of their cases are due to the Victoria lineage, which is not included in this year’s standard trivalent flu vaccine.

 

A bit of a surprise as the most recent WHO Influenza Surveillance Report (July 27th) found globally that detections of the B-Yamagata lineage continue to outnumber B-Victoria by nearly 20 to 1. ( `Of the characterized B viruses, 89 (94.7%) belonged to the B-Yamagata lineage and 5 (5.3%) to the B-Victoria lineage.’).

 

 

Eurosurveillance, Volume 20, Issue 31, 06 August 2015

Rapid communications

Increased prevalence of influenza B/Victoria lineage viruses during early stages of the 2015 influenza season in New South Wales, Australia: implications for vaccination and planning

Z Jennings¹, I Carter¹, K McPhie¹, J Kok ()^1,2,3, D E Dwyer^1,2,3

During the early weeks of the 2015 Australian influenza season, influenza B accounted for 67% (821/1,234) of all positive influenza tests in New South Wales. Of 81 successive influenza B viruses characterised, 33 (41%) were from children aged < 16 years; 23/81 (28%) belonged to the B/Victoria lineage. This lineage is not contained in the southern hemisphere's 2015 trivalent influenza vaccine. The significant B/Victoria lineage activity in the southern hemisphere suggests that the quadrivalent vaccine should be considered for the northern hemisphere.

 

The first four weeks of the 2015 influenza season in New South Wales, Australia (15 June to 12 July) have shown substantial early influenza B activity, with frequent detection of influenza B/Victoria lineage viruses, including in children (aged under 16 years). This lineage is not contained in the southern hemisphere’s 2015 [1] or the northern hemisphere’s 2015/16 trivalent influenza vaccine [2].

(Continue . . . )

 

Whether this activity in NSW is an outlier or a harbinger is far too soon to say.  The authors do, however, suggest this uncertainty may make the quadrivalent vaccine a better choice for the Northern Hemisphere this fall.

They conclude by writing:

 

Although the sample size of the present study is small, our preliminary data suggest early and significant B/Victoria lineage virus activity in children and adults in New South Wales. The recommended influenza B component of the 2015/16 northern hemisphere’s trivalent influenza vaccine is the B/Phuket/3073/2013-like virus (B/Yamagata lineage). As there may be incomplete protection against B/Victoria lineage infection for those receiving the trivalent vaccine, our early data would suggest that a quadrivalent vaccine should be considered for the upcoming northern hemisphere influenza season (and for travellers to the southern hemisphere). This will be especially relevant if the northern hemisphere experiences early and widespread influenza B/Victoria activity similar to that being observed in the current southern hemisphere winter.