chart, page-33

http://www.newscientist.com/article/mg20227073.500-swine-flu-can-science-save-us-from-the-second-wave.html?DCMP=OTC-rss&nsref=online-news


The 1918 flu started with a mild wave in March, followed by a deadly second wave later in the year. For the 2009 virus to follow the same path, two things need to happen: the virus has to spread readily enough in humans that it does not fizzle out, and it needs to mutate to a nastier form capable of killing more people.

It seems unlikely that this virus will simply fizzle out, as it has already managed to persist for months. Mike Worobey of the University of Arizona at Tucson has analysed the genetic divergence of virus samples from different cases to estimate their most recent common ancestor, a minimum estimate of when the virus jumped to people. He says that it probably appeared sometime between June and November last year, and at the end of November at the latest.

Assuming it stays, will it get nastier? There are no signs the virus is undergoing unusually rapid evolution in humans, Worobey says, which is good news, although that may yet change.

...

One difference between 1918 and now is the possibility of a vaccine. In theory, if this mild outbreak of H1N1 is followed by a lethal wave later in the year, we could make vaccines against what is circulating now and hope they still work against whatever the virus turns into.

Can we make enough vaccine in time? Production of ordinary flu vaccine for the next northern winter is well under way, and the plan, says the World Health Organization, is to finish this run and then turn the factories over to H1N1 vaccine, which could happen as early as June.

However, an unpublished study of global vaccine manufacturing capacity commissioned by the International Federation of Pharmaceutical Manufacturers and Associations suggests this isn't enough time. If production begins in June under the best possible conditions, we could have 190 million doses by September, jumping to a billion by October, not nearly enough for the world's people.

Another option is antiviral drugs, but supplies are limited and the virus is expected to develop resistance to Tamiflu.


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The incubation period appears to be between 5 and 7 days. The infectious period is not known.

There also appears to be a H3N2 flu in circulation and may be the source of the severe illness in Mexico

http://www.npr.org/blogs/health/2009/05/second_strain_might_have_cause.html

A posting on effect measure indicates that the flu is following an "exponential curve pretty well, with an increase by a factor of 1.35 per day".

Given that not all cases are being tested, it is probably more than this.

Most of the increase is in the US. Warm temperatures may break this trend.


M