|Researchers Find Surprising Pattern of Influenza
Spread in South America and Tropics
Researchers studying influenza transmission patterns in the Southern
Hemisphere and in tropical areas, specifically Brazil, uncovered
the unexpected finding that each season influenza travels from
low populated regions near the equator to the more populated centers.
Their work, funded by the Fogarty International Center (NIH), part
of the National Institutes of Health (NIH), can improve planning
for influenza control in tropical areas.
In their paper, "Seasonality of Influenza in Brazil: A Traveling
Wave from the Amazon to the Subtropics," to be published in the
American Journal of Epidemiology, the researchers document the
seasonal spread of influenza viruses and seasonal mortality patterns
associated with influenza across Brazil. The interest in Brazil
arises because the country covers a range of latitudes and crosses
several regions, including tropical and sub-tropical climates.
"This study contributes to the understanding of the role of tropical
regions in the global circulation of influenza. It has direct implications
for public health by offering guidance for the timing of delivery
and composition of influenza vaccines," said Dr. Mark Miller, a
co-author and Associate Director for Research at FIC.
As epidemic months of influenza in Brazil are triggered earlier
in the year in the equatorial regions, vaccine recommendations
using formulations from the Northern Hemisphere could be more appropriate
for some countries in the Southern Hemisphere near the equator.
This point is becoming increasingly important as more tropical
countries introduce and use substantial quantities of vaccine.
Brazilian investigators worked with colleagues at FIC and the
National Institute of Allergy and Infectious Diseases (NIAID) in
revealing the unexpected spatial transmission patterns in the annual
seasonality of influenza across a large area of the South American
Brazil is nearly the same size as the United States. However,
most of Brazil's territory lies in the tropical belt. This aspect
makes the study valuable since less is known about the circulation
of influenza viruses at these latitudes and how epidemics bridge
and annually alternate between both hemispheres following the winter
Given the range of latitude encompassed by Brazil which crosses
the equatorial and the southern tropic lines and using sophisticated
mathematical analytical tools, the researchers studied the mortality
data of influenza and pneumonia from two decades, together with
laboratory confirmed data from recent years.
Both sets of independent data sources converged to show that,
surprisingly, in Brazil influenza epidemics do not spread from
where the highest human population densities are found, but rather
from the equator towards more populous regions of the Southeast
and South of Brazil.
The study, supported by FIC, results from a collaboration among
researchers in different parts of the world. Study authors are
Wladimir J. Alonso (FIC), Cécile Viboud (FIC), Lone Simonsen (NIAID),
Eduardo W. Hirano (Mechanical Engineering Department, Universidade
Federal de Santa Catarina, Florianópolis, Brazil), Luciane Z. Daufenbach
(Secretariat of Health Surveillance, Ministry of Health, Brasília,
Brazil), and Mark A. Miller (FIC).
the international component of the NIH, addresses global health
challenges through innovative and collaborative research and training
programs and supports and advances the NIH mission through international
is a component of the National Institutes of Health. NIAID supports
basic and applied research to prevent, diagnose and treat infectious
diseases such as HIV/AIDS and other sexually transmitted infections,
influenza, tuberculosis, malaria and illness from potential agents
of bioterrorism. NIAID also supports research on basic immunology,
transplantation and immune-related disorders, including autoimmune
diseases, asthma and allergies.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.