Study of first wave of swine flu requiresrevised public health strategies29 June 2009

There is no way to know how the newest strain ofthe H1N1 influenza virus will behave in the future.But scientists, notably those working at theintersections of epidemiology, mathematics,modeling and statistics, are monitoring it closely toidentify anomalies on its pattern of spread whileevaluating ways of mitigating its impact.

"Public health officials have the ability to trackconfirmed cases and hospitalizations in real-timewith modern data collection approaches and theaid of modeling as well as the ability to quicklyidentify new strains and track their evolution," saysmathematical epidemiologist Gerardo Chowell-Puente, an assistant professor at Arizona StateUniversity's School of Human Evolution and SocialChange in the College of Liberal Arts andSciences.

Chowell-Puente is co-author of a new study of theA(H1N1) influenza pandemic strain circulatingaround the world. The study's findings reveal anage shift in the proportion of cases toward ayounger population when compared with historicalpatterns of seasonal influenza in Mexico. Thefindings are published June 29 online in the NewEngland Journal of Medicine. Other authors of"Reported severe respiratory disease and deathsconcurrent with atypical A(H1N1) influenzacirculation of swine origin in Mexico, 2009" includeStefano Bertozzi and Arantxa Colchero, Mexico'sNational Institute of Public Health; Hugo Lopez-Gatell, Celia Alpuche and Mauricio Hernandez,Mexico Ministry of Health; and Mark A. Miller,National Institutes of Health Fogarty InternationalCenter,

"The data show that the vast majority of cases ofsevere pneumonia and deaths occurred amongthose ages between 5 and 59, which is atypicalwhen compared with the age pattern supported byseasonal flu," says Chowell-Puente. "If resourcesor vaccine supplies are limited, focusing preventionefforts on these age classes must be considered."

Specifically, according to the findings, 87 percent ofthe deaths and 71 percent of the cases of severepneumonia occurred in persons aged 5-59,compared to an average 17 percent and 32percent, respectively, for influenza seasons from2006 through 2008. "These findings suggestrelative protection for those persons exposed toH1N1 influenza viruses during childhood prior tothe 1957 pandemic," Chowell-Puente says.

Chowell-Puente and other mathematicians andbiostaticians attending a swine flu workshop atArizona State University June 25-28, note thatvaccines and anti-viral medications are in limitedsupply.

"Because achieving high vaccination rates beforethe fall is not feasible with current technologies,effective distribution of a limited vaccine andantiviral stockpiles will be crucial to mitigate apotential second pandemic wave. The seasonalinfluenza vaccination strategy focuses on the veryyoung and the very old - the most vulnerablepopulations. This is not necessarily the case forpandemics as we showed in our study."

According to Chowell-Puente, the key to containingpandemic flu is closely tied in to the ability toquickly produce a good stockpile of vaccines andfollowing a reactive distribution plan that targets theappropriate age cohorts of the population. The firstwave of the current strain has not been particularlydeadly, but subsequent waves may be morevirulent, though it is too early to tell, he notes.

"For the 1918 ("Spanish flu") influenza pandemic,this was the pattern - first a mild wave, and then asevere one with higher case fatality rates," notesChowell-Puente.

The features of the A(H1N1) epidemic, according tothe findings, are "somewhat similar to pastinfluenza pandemics in that circulation of a new influenza virus is associated with an unseasonal

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wave of disease affecting a younger population."

It is the hope of Chowell-Puente that making thisdata available will help politicians make science-based decisions on how to optimize the use oflimited resources to manage this and futureepidemics.

In addition to this latest research, Chowell-Puentealso was a co-author on a recent study of the flu inJapan. "Here we looked at the public healthstrategies they used that essentially stopped thespread of the disease in its tracks," he says.

The researchers found that in Japan, more than 90percent of the cases were in school-aged childrenand teens. Quick action was taken to contain thedisease through school closures and other socialdistancing measures, such as avoiding use ofpublic transportation and the use of face masks. Inaddition, Japan employed active surveillance atairports, using recently developed sensors to detectpassengers with fevers for additional screening.The disease was contained within two-to-threeweeks, with only about 500 cases and no fatalities.Findings from this study appeared in the June 4issue of Eurosurveillance in an article titled"Transmission potential of the new influenzaA(H1N1) virus and its age-specificity in Japan."

Other authors on the Japanese study include:Hiroshi Nishiura, University of Utrecht, theNetherlands; Carlos Castillo-Chavez, Arizona StateUniversity; and Muntaser Safan, MansouraUniversity, Egypt.

Reducing the spread of the disease is key topreventing deaths, according to Chowell-Puente."As transmissibility grows, timely implementation ofcontrol measures is key to reduce epidemic impacton the population."

Source: Arizona State University (news : web)

APA citation: Study of first wave of swine flu requires revised public health strategies (2009, June 29)retrieved 22 April 2018 fromhttps://medicalxpress.com/news/2009-06-swine-flu-requires-health-strategies.html

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