Seroprevalence Following the Second Wave of Pandemic 2009 H1N1 Influenza. Ross, Zimmer, Burke, Crevar, Carter and Stark.

http://knol.google.com/k/seroprevalence-following-the-second-wave-of-pandemic-2009-h1n1-influenza?

I saw a recent Lancet paper that suggested an infection rate of 1 in 3 for children.

http://press.thelancet.com/h1n1inengland.pdf.

Didn’t the CDC report ~20% vaccination rate in the US population?

If we sum an estimated 60 million vaccinated and another 65 million who contracted the virus, with another 15-20% having some cross-protection from either pandemic or seasonal H1N1, the potentially protected CDC guesstimate of approximately half the US population sounds reasonable.

A possible explanation for the lack of a severe second wave in the US and Canada?

Blame the diminished global economy, at least in part. Slowdown in air travel, more people staying at home.

There has been a minor uptick in activity across North America and Europe in the past month: that’s the weather.

The lack of a expected heavy wave in the Southern Hemisphere was due to different factors at play.

Protracted wave propagation in Asia can also be blamed on the economy (flipside reasoning) and far-from-normal weather.

You do realize that had contributing factors not diminished this past Fall, the 2010 Winter Olympics in Vancourver might have been a disaster, coming in midst of what should have been a strong second wave of infection?

We are not out of the woods yet. The fickle and foolish general population may have thought the pandemic response by CDC and WHO to be overblown, but they haven’t a clue just how close we came to a real hummer infectious event: a minor gap between thumb and forefinger.

That close.

Very interesting: very low seasonal influenza rate. Higher in Asia. Hmmmm.

It makes sense, but it doesn’t fit into the observations worldwide that older people in general have immunity to the new SOIV. Since the swine flu vaccine wasn’t given outside North America (as far as I know, and I’m not positive about Canada even), it can’t account for the widespread immunity in older people in the UK and other places.

I think there’s just too many unknowns and not enough large studies to make strong a cases about the present impact of the 1976 vaccination, although it’s likely that there is at least some remaining impact.

As you say, we should not overstate the impact of the 1976 vaccine.

Just one last back of envelope calculaton… or… one last speculation really.

If around half of the remaining persons who were vaccinated in 1976 (persons age 27 and higher) survived to older age, (say another 13 million ?) could that possibly account for much of present-day pre-existing immunity among present day seniors, who number around 39 million ?

Thanks again,

Ed

Although it’s worth noting that even children in that study had around a 4% rate of pre-existing immunity. Who knows where that came from, but if it also affected the somewhat older cohort then there’s only an extra 2% that could be the 1976 vaccine effect.

The larger point (without getting bogged down in numbers that are not very precise to start with), I think, is that the 40 million vaccinees wouldn’t have as large an impact on pre-existing immunity as you’d think at first glance, even without taking into account the gradual loss of immunity over 33 years.