Study: 2009 H1N1 variant gained a foothold in three countries

Oct 21, 2010 (CIDRAP News) – Laboratory experts from Australia and Singapore have identified changes in the 2009 H1N1 flu virus that they say don't seem to make the vaccine less effective but bear watching.

Researchers first identified the genetic variants in April 2010 in Singapore, where they became more common, spreading to New Zealand and Australia during their winter flu seasons.

The group described its findings in today's issue of Eurosurveillance. Other experts contacted by CIDRAP News said the findings are not surprising.

Over the past several months, global health officials have said the circulating 2009 H1N1 strains are a good match with the ones included in the latest seasonal flu vaccines for both hemispheres.  The authors wrote that earlier genetic variants, D222G and E391K, have not predominated in a country or region like the new variations have.

They found that 2009 H1N1 viruses isolated this year from Singapore, New Zealand, and Australia showed the E391K change in the hemagglutinin protein, a further change in the HA (N142D), along with changes in the neuraminidase (NA) protein, M15I and N189S. Viruses with the changes became predominant in Singapore by the middle of 2010 and were found in New Zealand in July and August.

So far viruses with the HA changes have been detected only sporadically in other areas, such as Guam. Viruses with both the HA and NA changes have so far not been reported in any Northern Hemisphere countries.

In Australia and Singapore, the variant 2009 H1N1 viruses were associated with several vaccine breakthroughs (infections that occur in spite of vaccination) in teens and adults who received the 2009 H1N1 vaccine, as well as in a number of fatal cases.

However, the researchers said that without complete patient records they can't compare the breakthrough frequency of the variant and nonvariant strains. Also, a comprehensive review of patient record would reveal possible confounding factors, such as age and immune status.

When the investigators used hemagglutination inhibition (HI) assays to assess antigenic variation with the variant virus, they found no differences between it and reference and vaccine viruses. When they tested the variant against a small human serum panel, they found some reduction in HI titers with postvaccination sera, but, when considering both HI analyses, they said the findings suggest no major antigenic differences with the variant viruses in this stage of their evolution.

"It remains to be seen whether this variant will continue to predominate for the rest of the influenza season in Oceania and in other parts of the southern hemisphere and then spread to the northern hemisphere or merely die out," the group wrote.

Though the findings don't appear to represent a significant antigenic change, they might signal the start of a drift in the 2009 H1N1 virus that may require a vaccine update sooner than expected, they concluded.

Vincent Racaniello, PhD, a virologist at Columbia University who writes Virology Blog, told CIDRAP News that the findings aren't surprising: The virus is drifting genetically, but the amino acid changes haven't yet affected the antigenic structure of the virus.

He said the findings don't signal the start of antigenic drift, and there are no specific properties associated with the changes the researchers observed.

The data included in the study reflect a small fraction of the thousands of virus specimens World Health Organization (WHO) laboratories collect and study as they assess antigenic drift and whether a drifted strain is likely to spread in populations, Racaniello said.

Nancy Cox, MD, director of the Influenza Division at the US Centers for Disease Control and Prevention (CDC), told CIDRAP News that the data in the study are not new to the CDC. She said they came out of WHO collaborating centers and were reviewed over the summer and at the end of September when WHO experts made their recommendations for the Southern Hemisphere's 2011 flu season.

She added that the CDC constantly monitors circulating flu viruses for both genetic and antigenic changes.

See also:

Oct 21 Eurosurveillance report

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