Saturday, September 5, 2009

H1N1 - second wave?

I found the recent report in the Straits Times that the hospitals were gearing up for a second wave, somewhat intriguing

The report had cited an estimate that about 700,000 had already been exposed to H1N1 and was likely to have immunity. This estimate was based on a back calculation from WHO's estimate of case-fatalities, which was in all likelihood an overestimate, which means the 700,000 is probably an underestimate. But let's say that that represents a decent estimate.... the extrapolation would mean that based on a total population of 4.8 million, there remains another 4.1 million residents and non-residents without immunity.

So a second wave is not an unlikely event.

But as I pondered this with my mathematically challenged mind,.... I couldn't help wondering if the second wave may be reasonably expected to be greater or lesser than the first wave. It just seemed to me that all things being equal (i.e. that the virus hasn't changed) that a wave resulting form exposure to 4.1 million individuals with no immunity might be expected to be lesser than that arising from exposure to 4.8 million naive individuals. And if we had underestimated the numbers who have been exposed to the first wave, the numbers who remained vulnerable would be less ..... and the size of the expected second wave would be correspondingly muted.

So is a panic warranted? I hardly think so, especially since the first wave wasn't even quite the tsunami predicted.

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