One of the persistent riddles of the deadly 1918 Spanish influenza pandemic is why it struck different cities with varying severity. What made the difference, according to two independent studies funded by the National Institutes of Health (NIH), was not only how but also how rapidly different cities responded.

Cities where public health officials imposed multiple social containment measures within a few days after the first local cases were recorded cut peak weekly death rates by up to half compared with cities that waited just a few weeks to respond.

Overall mortality was also lower in cities that implemented early interventions, but the effect was smaller. These conclusions -- the results of systematic analyses of historical data to determine the effectiveness of public health measures in 1918 -- are described in two articles published Monday online in the journal Proceedings of the National Academy of Sciences.

The papers suggest that a primary lesson of the 1918 influenza pandemic is that it is critical to intervene early, says Anthony S. Fauci, M.D., director of NIH"e;s National Institute of Allergy and Infectious Diseases (NIAID), which funded one of the studies.

While researchers are working very hard to develop pandemic influenza vaccines and increase the speed with which they can be made, non-pharmaceutical interventions may buy valuable time at the beginning of a pandemic while a targeted vaccine is being produced.

Non-pharmaceutical interventions may limit the spread of the virus by imposing restrictions on social gatherings where person-to-person transmission can occur.

The first of the two historical studies, conducted by a team of researchers from NIAID, the Department of Veterans Affairs, and the Harvard School of Public Health, looked at 19 different public health measures that were implemented in 17 U.S. cities in the autumn of 1918.

The second study, undertaken at Imperial College London, looked at 16 U.S. cities for which both the start and stop dates of interventions were available.

Schools, theaters, churches and dance halls in cities across the country were closed. Kansas City banned weddings and funerals if more than 20 people were to be in attendance. New York mandated staggered shifts at factories to reduce rush hour commuter traffic. Seattle"e;s mayor ordered his constituents to wear face masks.

The first study found a clear correlation between the number of interventions applied and the resulting peak death rate seen.

The second study also shows that the timing of when control measures were lifted played a major part. Cities that relaxed their restrictions after the peak of the pandemic passed often saw the re-emergence of infection and had to reintroduce restrictions, says Neil Ferguson, D.Phil., of Imperial College, London, the senior author on the second study.

The fact that the early, non-pharmaceutical interventions were effective at the height of the pandemic can inform pandemic planners today, the authors of both studies say.

Source: Xinhua