Study shows equatorial regions in Brazil less affected by 2009 influenza pandemic

The death toll of the 2009 influenza pandemic in equatorial climates may have been much lower than originally thought, according to a study supported by the National Institutes of Health's Fogarty International Center. The paper, published in PLoS ONE, challenges the idea that the pandemic was deadlier in the tropics, which harbor nearly half of the world's population and which have the highest burden of infectious disease.

The study may have a direct bearing on global estimates of pandemic burden and on the assessment of immunological, socioeconomic and environmental drivers of the outbreak, according to Fogarty researcher Dr. Wladimir J. Alonso, who led the study. The authors stressed that comparing disease burden as reliably as possible is critical in areas with competing health priorities and limited resources, as is the case for Brazil and other countries in the equatorial region.

Alonso's group of epidemiologists found evidence of far milder and delayed towards areas of Brazil closer to the . "We found that respiratory mortality was substantially higher during the pandemic in the southern and richer half of Brazil, where its circulation coincided with the colder winter months," said Alonso. "But even more puzzling, little or no difference from pre-pandemic mortality levels was identified in equatorial regions."

To arrive at these estimates, the researchers investigated laboratory-confirmed pandemic deaths in each Brazilian state and estimated the mortality burden caused by the pandemic that was above what would be expected in an average year. The analytical approach they employed determined baseline mortality in pre-pandemic years by considering the usual variability—including that of seasonal epidemics—in each location, and let them compare the impact of the pandemic across areas with different climatic and epidemiological profiles.

The observed difference in pandemic mortality spanned more than 2,700 miles and was independent of social and demographic factors, with lower-income states being less affected by the pandemic. The findings also suggested that, similar to seasonal , climate played a key role in the dynamics of the outbreak.

The researchers included data going back to 1996, using mortality statistics from two independent sources maintained by the Brazilian government. "Brazil represents a unique opportunity, as it has a large population dispersed across climate zones and yet also exposed to uniform immunization and mitigation efforts," said Dr. Cynthia Schuck-Paim, director of Origem Scientifica Ltd. Data Analysis in Sao Paulo, Brazil, and the lead author of the article.

According to Alonso, the study is the first to generate such results. "The finding that the severity and timing of circulation of this strongly depended on latitude does not imply that future pandemics will behave similarly," Alonso said. "Research on other past pandemics, such as the flu that swept the globe in 1918 and killed an estimated 50 million people, is also crucial for the elaboration of better preparedness plans."

add to favorites email to friend print save as pdf

Related Stories

Earliest known evidence of 1918 influenza pandemic found

Sep 19, 2011

Examination of lung tissue and other autopsy material from 68 American soldiers who died of respiratory infections in 1918 has revealed that the influenza virus that eventually killed 50 million people worldwide was circulating ...

Study challenges notion of 'pandemic' flu

Apr 14, 2008

The widespread assumption that pandemic influenza is an exceptionally deadly form of seasonal, or nonpandemic, flu is hard to support, according to a new study in the May issue of the American Journal of Pu ...

Measuring the uncertainties of pandemic influenza

Jul 02, 2012

A major collaboration between US research centers has highlighted three factors that could ultimately determine whether an outbreak of influenza becomes a serious epidemic that threatens national health. The research suggests ...

Recommended for you

Ebola mistakes should serve a lesson says WHO

14 hours ago

The World Health Organization's chief admitted on Sunday that the UN agency had been caught napping on Ebola, saying it should serve as a lesson to avoid similar mistakes in future.

British Ebola nurse discharged from hospital

20 hours ago

A British nurse who contracted Ebola while working as a volunteer in Sierra Leone said she was "happy to be alive" as she was discharged from hospital on Saturday having made a full recovery.

Tide turning in Ebola fight after hard lessons

Jan 24, 2015

A top U.N. official in the fight against Ebola greeted just three patients at one treatment center he visited this week in Sierra Leone. Families in Liberia are no longer required to cremate the remains of ...

Just five Ebola cases left in Liberia: UN

Jan 24, 2015

The United Nations said on Saturday Liberia was dealing with just five remaining cases of Ebola, in the clearest sign yet that the country is nearing the end of the outbreak.

User comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.