Severity of H1N1 Reassesed

Study finds that the H1N1 virus may harm fewer Americans than earlier anticipated

The current H1N1 outbreak in the U.S. may be much less severe than originally anticipated, according to a recent study conducted by researchers at the Harvard School of Public Health and the UK Medical Research Council.

This is the most up-to-date study that attempts to quantify the impact of the H1N1 virus, the impact of which has been steadily decreasing in severity since it first hit the U.S. this April.

“The overall message of this study is that, though individuals should still take cautions, the overall impact on our society is fortunately less severe than the upper end of what we thought was possible,” said Marc Lipsitch, one of the study’s authors and a professor of epidemiology at HSPH.

Lipsitch heads the HSPH Center for Communicable Disease Dynamics, established this September to research infectious disease, track their outbreaks, and make information more available to policy makers and the public.

Using data collected from the city health departments of Milwaukee and New York City from April to July this year and from the Centers for Disease Control, the researchers obtained a ratio of deaths to H1N1 cases.

Using two different methods of calculation, the researchers determined two mortality rate estimates, with the higher measure reaching one death out of every 2000 cases, which is about four to ten times less than initial projections.

“Both estimates were in the low ranges of what the CDC originally thought was possible,” Lipsitch said.

The H1N1 virus is still quite a serious public health threat, Lipsitch said, but he added that the study’s results could be helpful for health officials in better gauging the necessary resources and precautions needed to combat the virus. For example, these results could be used to justify decisions not to close schools in large numbers.

“It is important not to make an incredibly costly, large-scale response that would have been disproportionate to the scale of the threat,” he said. “It was right to be cautious early on, but backing off slightly may be appropriate.”

Soheyla D. Gharib, the chief of medicine at Harvard University Health Services, said she has seen a slight decline in the number of students coming into the clinic with flu-like symptoms. She added, however, that the downturn could be due to the beginning of reading and exam period, when students are often too busy to visit UHS.

In light of the study, Gharib said that it is possible that the CDC could downgrade the H1N1 virus’s threat level to seasonal flu status or to relax procedural guidelines.

“But until then, Harvard will continue to follow CDC guidelines to manage the outbreaks on campus,” Gharib said.

The study was funded by the National Institutes of Health and was published online on December 7, 2009 in the journal PLoS Medicine.

—Staff writer Helen X. Yang can be reached at