WHO announcement of recommended strains to be included in the Southern Hemisphere 2012 influenza vaccine compositionArchived

ECDC comment

The World Health Organization (WHO) recently recommended using the same three flu strains in next year's Southern Hemisphere (SH) vaccine as are in the current Northern Hemisphere vaccine and were used last year in southern hemisphere countries.

The World Health Organization (WHO), Switzerland, Geneva –September 2011

 The recommendation, which has been published on WHO’s website as a technical report, means the experts assembled by WHO did not see enough evidence of changes in circulating flu strains that would justify changing the antigens in the coming 2012 vaccine. It was recommended to keep the pandemic 2009 strain for the influenza A/H1N1 component of the vaccine, along with a Perth 2009 strain of A/H3N2 and a Brisbane 2008 strain of influenza B.

The recommendation was that vaccines should contain the following three antigens:

  • A/California/7/2009(H1N1)pdm09
  • A/Perth/16/2009 (H3N2)
  • B/Brisbane/60/2008

This means the WHO has chosen the same three strains for the Southern Hemisphere 3 years in a row, as the agency first chose them in September 2009 for the 2010 season.

The report gives a good description of the strains that circulated in the 2011 Southern Hemisphere winter. The A(H1N1) 2009 influenza virus co-circulated in varying proportions with H3N2 and type B viruses from February to September, with widespread activity in many countries. This year activity was generally ‘low or moderate’. Yet again no isolates of the previous seasonal A(H1N1) strain were found. The report also mentions that the circulating 2009 A(H1N1) influenza viruses have remained antigenically and genetically similar to the California strain in the current vaccine, and the majority of recent A(H3N2) isolates have been similar to the Perth strain in the vaccine. Influenza B viruses come in two lineages, Victoria and Yamagata, and predicting which will predominate in any given season has been difficult. The Brisbane 2008 strain in current vaccines is a Victoria strain. The report noted that Victoria strains have predominated recently in many parts of the world and have been closely related to the vaccine strain, while Yamagata variants were more common in northern China from February to May.

ECDC Comment (October 10th):

This report also notes how the majority of 2009 A(H1N1) influenza viruses have remained sensitive to the antiviral drug oseltamivir. Of the resistant isolates, most were associated with use of the drug for prevention or treatment. However it is also noted how in the United States, the United Kingdom and Japan in 2010-2011 there were small proportions of resistant cases with no known exposure to oseltamivir. This suggest limited person to person transmission of virus. This was also noted in parts of Australia in 2011 suggesting a need for careful vigilance in the light of what happened in Europe in 2007-8 when oseltamivir resistance emerged and predominated rapidly.(1)

One issue now is what to call the A(H1N1) viruses from the 2009 pandemic. Given that they are the only human A(H1N1) viruses circulating there must be an argument for calling them just human A(H1N1) viruses rather than the cumbersome A(H1N1)pdm or A(H1N1)2009 outside of the full scientific  naming (like  A/California/7/2009(H1N1)pdm09).

(1). Meijer A, Lackenby A, Hungnes O, Lina B, van der Werf S, Schweiger B, et al. Oseltamivir-resistant influenza A (H1N1) virus, Europe, 2007–08 season. Emerg Infect Dis. 2009 April