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Paradigm Shift Intervention Monitoring
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Absenteeism Linked To H1N1
Wave 3 Start
The above comments on H1N1 antibody frequencies in Allegheny County indicate that H1N1 rapidly spread through the Pittsburgh, Pennsylvania metropolitan area last fall, especially among school aged children, aged 10-19. Although there were few school closures or deaths a few schools were highlighted in media reports and in one middle school daily absenteeism rates were between 19-29% for at least 9 days, suggesting attack rates approached 100% since many who were affected did not develop a high fever and were not absent.
Other areas reported closures of entire school districts suggesting these high levels were present nationwide during the fall peak in activity. That peak began with school opening in August for many areas of region 4, and recent reports suggest a new wave may have begun there which has now started to spread nationwide. Although media reports had announced the end of the pandemic and some politicians questioned whether there was a pandemic, prior pandemics had a fall and winter wave and eliminated the seasonal flu that had been circulating.
Pandemic H1N1 has eliminated seasonal influenza A, which sets the stage for a new wave, which may be beginning. The fall wave was generated because most of the target population had no existing immunity to the new H1N1 and the development of immunity led to the end of the fall wave. However, low reactors have been identified pointing toward the emergence of a new wave with H1N1 that avoids the immunity generated against the H1N1 circulating in the fall.
One of the low reactors, D225G, was tightly linked to fatal cases in the fall, and recent sequences from Italy and Russia pairs that change up with another low reactor change, G158E, raising concerns that such recombinants can evade the existing immunity and generate cases which are more severe and fatal.
Recent reports in Tennessee and North Carolina have described patients with a higher frequency of ICU admissions and deaths and recent increases in other states in Region 4 raise concerns that these trends could spread. A 52% rise in weekly cases in colleges has been reported and the highest number was in North Carolina. Moreover, junior high schools are now reporting double digit absenteeism in Washington state. These increases in populations that were targeted in the fall raise additional concerns regarding the emergence of variants that have escaped the immunity generated last fall.
Sequence data on the emerging H1N1 would be useful.