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WHO H1N1 Pandemic Alert - 2009 and 2011

Recombinomics Commentary 17:30
April 26, 2011

At the request of the Director-General (DG) of WHO, the IHR Emergency Committee has been summoned and is advising the DG on the event. On its first day of deliberation, 25 April, it concluded that the present event constitutes a public health emergency of international concern. To date, no temporary recommendations have been made. The Emergency Committee will continue to advise the DG on the basis of the available information.

Considering the possibility of an outbreak occurring on account of the influenza A (H1N1) 2009 virus in the countries of the Region, national authorities should be prepared to mitigate the resulting impact. It is recommended that all of the countries activate their National Preparedness Plans for the pandemic and follow the WHO and PAHO recommendations.

The two paragraphs above are from WHO H1N1 pandemic alerts almost exactly two years apart, in 2009 and 2011, respectively.  The two alerts have much in common, but there are significant differences.

In 2009 the first two confirmed cases were two children in southern California, who had no reported contact with swine or each other, but were infected with virtually identical swine derived H1N1 as determined by the United States CDC.  Similar sequences were identified in Canada from samples from patients in Mexico, which was followed by confirmation of multiple cases in multiple states in the US. 

Thus, the April 25, 2009 alert had already met the sustained transmission requirement for the declaration of a pandemic.  However, the phase definitions had been revised and sustained transmission was lowered to phase 4, with transmission in are large region, such as North and South America representing phase 5, and sustained transmission in additional unconnected continents as representing phase 6.  Thus, the official declaration of a pandemic was delayed for almost 2 months, largely because transmissions in other continents were linked to travelers from North and South America and community transmission was required for sustained transmission in another continent, and testing was largely limited to travelers, so the official pandemic declaration was delayed.

The H1N1 spread worldwide in the spring of 2009 and increase in degree and severity in the fall of 2010, when activity peaked prior to widespread vaccine distribution.

In August of 2010 the pandemic phase was declared over, in part because of a re-emergence of H3N2 and influenza B, which had been largely crowded out pandemic H1N1.  however, the H1N1 was still circulating and killing previously healthy young adults as it evolved away from immunity generate by infection or the A/California/07/2009 vaccine.

The new H1N1 alert is due to a novel sub-clade that emerged in Chihuahua, Mexico.  This sub-clade caused concern because of the death or two traffic officers (26M and 36M) in Juarez, who were partners and previously healthy.  Other members of the department were hospitalized, including at least one in critical condition.  The sub-clade had two receptor binding domain changes (A189T and D225N) raising concerns of immunological escape of a more virulent sub-clade.  These concerns were increased by another Chihuahua isolate which had D225N and D225G, as well as anecdotal reports of multiple additional isolates in Chihuahua with D225N, and similar results in other countries in South America.

Thus, the current alert has the potential of being considerably more serious because of prior immunological escape and no current alternative vaccine, as well as a higher frequency of D225N, which is associated with more severe and fatal cases.

Like, 2009, an aggressive vaccination campaign has been launched to blunt the untimely emergence of a novel H1N1, however, it is not clear that the current vaccination efforts will control the spread of a rapidly evolving H1N1.

Release of the Chihuahua sequences with D225N, as well as sequences from severe and fatal cases in the current outbreaks in North and South America would be useful.

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