Levels of exposure 10 times higher than previously expected.

indigo girl · Jan 22, 2010

New data on how much infection in the first wave of the pandemic

It was some time after the pandemics of 1957 and 1968 that we were able to judge their severity and it will likely be some time after this one has finally burned itself out, most likely to become "just another" seasonal flu, that we will be able to gauge the 2009 swine flu pandemic. A lot of data is being generated but it will take time to harvest it and send it to the scientific market for consumption. A report in today's Lancet reminds us that we aren't seeing all there is to see, even with unprecedentedly rapid means of communication and better surveillance than ever in the history of our long battle with the influenza virus...
This study used blood samples drawn in 2008 (before the pandemic struck) to measure the prevalence of antibody in various age groups thought to sufficient to protect against the swine flu virus that emerged in 2009. We don't know the source of the low level of reacting antibody seen in a percent or two of children at that time (it is likely from cross reaction with another flu virus) but it is pretty clear that the circulating pandemic virus caused the ten fold increase seen in children after the first wave struck around London the spring and summer of the following year. Not all areas of England were equally affected nor were all ages. Increases in antibody prevalence in young adults and older age groups were much less and negligible in the oldest group...
These data confirm what models predicted and everyone suspected: there was much more infection with this virus than suggested by only counting clinical cases. Seasonal flu infections are clinically often very mild or even asymptomatic. That's good news for most people but the bad news is that when millions of people are infected it doesn't take a very high rate of more severe outcomes to fill up hospitals or empty schools and workplaces. Exactly why some people fare worse (or better) than others is not understood. We know there are some risk factors that increase your chances of a bad outcome, just as with severe auto accidents speed and alcohol are risk factors. Unfortunately they are not the sole predictors and thousands of people are killed or crippled on the road every year even though they weren't driving too fast or under the influence. Similarly, influenza, especially pandemic strains, can kill otherwise healthy people of any age, and this year has seen many such tragic cases.

Full commentary at:

http://scienceblogs.com/effectmeasure/2010/01/new_data_on_how_much_infection.php

The Editors of Effect Measure are senior public health scientists and practitioners. Paul Revere was a member of the first local Board of Health in the United States (Boston, 1799). The Editors sign their posts "Revere" to recognize the public service of a professional forerunner better known for other things.