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Commentary
H1N1 Attack Rate
Raises Pandemic Concerns
Recombinomics
Commentary 22:12
October15, 2009
High School - 7.6%
Mt. Royal Middle - 19%
Scott Ave. Elem. - 24%
Burchfield - 14%
Jeffery - 11%
Marzolf - 18%
Reserve - 12.5%
Rogers 14.5%
On Friday, the Middle School was 29% and was the school last week that started the week at 20% so it seems to be coming down which is a good sign.
The above comments from the website of a school district (Shaler) in suburban Pittsburgh, raise concerns that the H1N1 attack rate may be approaching 100% for some groups, such as middle school students. Most cases in the area (see map) are mild, and school days missed are limited because fevers generally last for only a few days. Consequently, most students only miss 1-3 days of school, so an absentee rate between 19-29% for more than 10 days suggest that more than 50% of the students were absent for 1 or more days. However, many students will not miss school because of a 3 day weekend or because they do not develop fever, so the number of infected students may be much high than 50% and may be approaching 100%.
This high attach rate is support by media reports on other schools which have peak absentee rates between 30-50%, as well as the increasing numbers of school closings. In Texas alone agency reports list 85 schools closed and high numbers have also been reported in other states such as TN and KY and additional schools are now being reported in states where the school season began more recently.
This dramatic spread has happened prior to widespread vaccinations, and signal efficient transmission, which may be blunted by an aggressive vaccination program. However, only a small percentage of ordered doses have been shipped and it is likely that significant transmission will happen prior to vaccination. Most of these cases have been mild, and data from the clinical trial in Australian suggest that mild cases can produce modest immune responses which are increased by the vaccine.
However, this high attack rate raises concerns of re-infection of mild cases as well as the evolution of virus which produces reduced titers to the current vaccine as was noted in the week 37 CDC report.
More detail on the number of student infected in a single outbreak and the level of antibody in the milder cases would be useful.
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