Oct 1, 2012 (CIDRAP News) – The World Health Organization (WHO) is recommending that influenza vaccines for the Southern Hemisphere's 2013 flu season should contain the same three strains as the vaccines now being administered to millions in the Northern Hemisphere.
The recommendation means that two of the strains will be different from those that were used in Southern Hemisphere vaccines this year. When the WHO issued a recommendation for the 2012-13 northern vaccine in February, it called for changing the influenza A/H3N2 and B strains that were used in this year's southern vaccines.
The new recommendation signals that the WHO is seeing few hints of emerging flu strains that could spread widely and evade the 2012-13 vaccine formulation.
The WHO experts make their recommendations for Southern Hemisphere flu vaccines in October to allow time to prepare the vaccine viruses and grow them in eggs, which takes several months. The recommendation for the Northern Hemisphere vaccine is usually made in February.
The agency recommended keeping the pandemic 2009 H1N1 (pH1N1) virus in the vaccine. Officially, the agency advises using strains similar to:
- A/California/7/2009 (H1N1)pdm09 (the pandemic 2009 virus)
- A/Victoria/361/2011 (H3N2)
The pH1N1 virus has been included in every WHO flu vaccine recommendation since September 2009, when it picked the strain for the 2010 Southern Hemisphere vaccine.
The recommendation is accompanied by a review of flu activity from February through September. Pandemic 2009 H1N1 activity during that period was generally low, and especially so in Africa, Europe, and Oceania, the agency said. All seasonal H1N1 viruses detected were the pH1N1 strain. The "vast majority" of pH1N1 viruses that were analyzed were found to be closely related to the 2012-13 (northern) vaccine strain.
Most countries had some level of H3N2 activity, with many parts of the Southern Hemisphere seeing widespread and regional outbreaks between May and August. Tests showed that most of the H3N2 viruses were closely related to A/Victoria/361/2011, the strain in the 2012-13 vaccine.
Many countries in both hemispheres reported influenza B activity in the past 8 months, with viruses from both lineages—Victoria and Yamagata—circulating. "Viruses of the B/Victoria/2/87 lineage were prevalent in some countries, while the B/Yamagata/16/88 lineage viruses have increased in some and predominated in others," the WHO says.
Predicting whether Victoria or Yamagata strains will be more common in any given flu season is difficult, which has prompted some manufacturers to move toward including both strains in their vaccine. In March the US Food and Drug Administration approved a quadrivalent vaccine from MedImmune Inc., which makes live attenuated vaccines delivered via nasal spray. The company said then it expects to have the vaccine ready for the 2013-14 season.
The B/Wisconsin/1/2010 strain that is in the 2012-13 vaccine and was picked for the 2013 southern version is of the Yamagata lineage. But for companies looking to make a quadrivalent (four-strain) vaccine with two B strains, the WHO recommends including a B/Brisbane/60/2008-like virus, which is of the Victoria lineage and was used in 2012 Southern Hemisphere vaccines.
The WHO recommendation suggests that the agency's experts are not concerned that the swine-origin variant H3N2 (H3N2v) viruses seen lately in the United States will spread. More than 300 H3N2v cases have been reported in recent months, nearly all of them in people who had contact with pigs at county and state fairs. H3N2v viruses carry the matrix gene from the pH1N1 virus.
Officials with the Centers for Disease Control and Prevention have said they've seen a few instances of limited human-to-human transmission of H3N2v but no sustained human transmission. The WHO review of flu activity notes the H3N2v cases but does not comment on them.
The WHO report also notes that 17 confirmed human H5N1 cases, with 10 deaths, occurred from February through September. Countries and territories reporting cases were Bangladesh, Cambodia, Hong Kong, Egypt, Indonesia, and Vietnam.
In other data, 1.4% (16 of 1,124) of pH1N1 viruses that were tested were resistant to oseltamivir, and most of the resistant isolates were not associated with use of the antiviral, according to the WHO. Only one H3N2 isolate and one type B isolate were found to show reduced susceptibility to neuraminidase inhibitors.
September 2012 WHO report and recommendation
Feb 23 CIDRAP News story on selection of strains for 2012-13 Northern Hemisphere vaccine
Oct 3, 2011, CIDRAP News story on strains picked for 2012 Southern Hemisphere vaccine
Mar 1 CIDRAP News story about FDA approval of MedImmune's quadrivalent flu vaccine