World Health Organization wrote:
>
Preparing for the second wave: lessons from current outbreaks
> Pandemic (H1N1) 2009 briefing note 9
> 28 AUGUST 2009 | GENEVA -- Monitoring of outbreaks from different
> parts of the world provides sufficient information to make some
> tentative conclusions about how the influenza pandemic might
> evolve in the coming months.
> WHO is advising countries in the northern hemisphere to prepare
> for a second wave of pandemic spread. Countries with tropical
> climates, where the pandemic virus arrived later than elsewhere,
> also need to prepare for an increasing number of cases.
> Countries in temperate parts of the southern hemisphere should
> remain vigilant. As experience has shown, localized “hot spots” of
> increasing transmission can continue to occur even when the
> pandemic has peaked at the national level.
> H1N1 now the dominant virus strain
> Evidence from multiple outbreak sites demonstrates that the H1N1
> pandemic virus has rapidly established itself and is now the
> dominant influenza strain in most parts of the world. The pandemic
> will persist in the coming months as the virus continues to move
> through susceptible populations.
> Close monitoring of viruses by a WHO network of laboratories
> shows that viruses from all outbreaks remain virtually identical.
> Studies have detected no signs that the virus has mutated to a
> more virulent or lethal form.
> Likewise, the clinical picture of pandemic influenza is largely
> consistent across all countries. The overwhelming majority of
> patients continue to experience mild illness. Although the virus
> can cause very severe and fatal illness, also in young and healthy
> people, the number of such cases remains small.
>
http://www.who.int/entity/csr/disease/s ... index.html