Public health interventions could cut deaths in event of flu pandemic

New analyis of spanish flu in the early 1900s could help plan for a future influenza pandemic<em> - News Release</em>

Imperial College London News Release
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17.00 EDT / 22.00 BST Monday 2 April 2007

Implementing public health interventions in the event of an emerging flu pandemic could have a major impact on mortality, according to new research in the journal PNAS analysing how US cities dealt with the 1918-19 Spanish influenza pandemic.

The new study shows that there were fewer deaths in 1918 in those US cities which implemented non-pharmacological interventions (NPIs) early on during the 1918 pandemic. The pandemic killed 600,000 people in the US and up to 50 million people worldwide.

NPIs limited contact between people in order to reduce the spread of the flu virus, which spreads from person to person in small droplets created by coughing and sneezing. The research, which examined 16 US cities, demonstrates that infection rates were often reduced by more than 30% while NPIs were in force.

The study was carried out by researchers from the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial College London, and the University of Utrecht.

In 1918 - 1919 600,000 people were killed by the Spanish flu epidemic in the USA alone

In 1918, many US cities closed schools, theatres, churches and dance halls; Kansas City banned weddings and funerals involving more than 20 people; and San Francisco and Seattle ordered their citizens to wear face masks.

However, such measures were often imposed much too late, when the epidemic had run half its course, and then lifted too soon, according to the study. Exceptions to this included San Francisco and St Louis, which imposed measures early and kept them in force through to January 1919. The researchers estimate that this reduced deaths by 25% or more.

The researchers suggest that interventions in the event of a present day pandemic would save the most lives if kept in place until a vaccine becomes available to protect the population.

In 1918, mortality peaked twice in some cities which had introduced NPIs, whereas it peaked only once in areas where the NPIs were not particularly stringent. The researchers suggest that in those areas with two peaks, the first wave of transmission was stopped so effectively that once controls were lifted, there were substantial numbers of individuals who had not developed any immunity. Transmission restarted in these people, leading to a second epidemic wave.

Professor Neil Ferguson, Director of the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial College London and corresponding author on the paper, said: "Our results show that non-pharmaceutical interventions may substantially slow the spread of a pandemic in countries like the UK so long they are aggressively implemented and introduced as soon as the virus is circulating in the country. However if we want these measures to save substantial numbers of lives they really need to be kept in place until we have enough vaccine to immunise the population.

"There would be huge social and economic consequences of imposing such measures for the 3 or more months that might be required for optimal effect. This may be warranted if we are faced with a highly lethal virus but it will be important to tailor our response to meet the threat we encounter at the time - and to make best possible use of antiviral stockpiles to both reduce deaths and infections and so reduce our reliance on disruptive non-pharmaceutical interventions," he added.

The researchers collected historical records from 16 US cities on the timing of control measures and the weekly death rates. They then developed a mathematical model of the 1918 pandemic in those cities and showed that the complex epidemic patterns seen in different cities could be explained by the differences in the timing and effectiveness of interventions. They went on to estimate how effective the combinations of interventions used were in reducing transmission and therefore deaths.

Whilst the researchers believe that much can be learned from the 1918 epidemic, they do advise a degree of caution in extrapolating from 1918 to the current day. Household sizes were much larger and many workers lived in large, crowded boarding houses within which transmission was probably intense. Far more people interacted with large extended families, children spent many fewer years in full-time education, and there were different travel patterns. Overall infectious disease mortality was much higher than it is today.

The research was funded by the UK Medical Research Council, the US National Institutes of Health and the European Union. It was undertaken at Imperial College London by researchers from Imperial College and the University of Utrecht.

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Notes to editors:

1. "The effect of public health measures on the 1918 influenza pandemic in US cities" PNAS, 2 April 2007 Martin C.J. Bootsma(1); Neil M. Ferguson(2)*

(1) Mathematical Institute, Faculty of Sciences, Utrecht University, Budapestlaan 6, 3508 TA Utrecht, The Netherlands
(2) MRC Centre for Outbreak Analysis and Modeling, Faculty of Medicine, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK

*Corresponding author neil.ferguson@imperial.ac.uk

2. About Imperial College London

Rated as the world's ninth best university in the 2006 Times Higher Education Supplement University Rankings, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 11,500 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

With 62 Fellows of the Royal Society among our current academic staff and distinguished past members of the College including 14 Nobel Laureates and two Fields Medallists, Imperial's contribution to society has been immense. Inventions and innovations include the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of our research for the benefit of all continues today with current focuses including interdisciplinary collaborations to tackle climate change and mathematical modelling to predict and control the spread of infectious diseases.

The College's 100 years of living science will be celebrated throughout 2007 with a range of events to mark the Centenary of the signing of Imperial's founding charter on 8 July 1907.

Website: www.imperial.ac.uk

3. About the Medical Research Council

The Medical Research Council is dedicated to improving human health through excellent science. It invests on behalf of the UK taxpayer. Its work ranges from molecular level science to public health research, carried out in universities, hospitals and a network of its own units and institutes. The MRC liaises with the Health Departments, the National Health Service and industry to take account of the public's needs. The results have led to some of the most significant discoveries in medical science and benefited the health and wealth of millions of people in the UK and around the world.

www.mrc.ac.uk