April 3, 2014
Rise In Births Adds Fuel To The Fire When It Comes To Disease Epidemics
Rebekah Eliason for redOrbit.com – Your Universe Online
Vaccines save millions of lives each year, but there are still almost four million children under the age of five who die each year from vaccine-preventable diseases. Two doctoral ecology students from the University of Michigan are working hard to lower that number.
According to Micaela Martinez-Bakker and Kevin Bakker, large vaccination campaigns in the developing world that take seasonal birth rate fluctuations into account could have a major impact on reducing deaths from printable diseases such as measles by inoculating more unprotected infants.
"If you have lots of kindling, you can have a bigger fire, and that's essentially the role that these susceptible infants play during measles outbreaks. If lots of new births flood into the population before a measles epidemic peaks, they can add fuel to the flames and make that year's epidemic bigger," said Martinez-Bakker, an NSF Doctoral Fellow whose work is supported by the US National Science Foundation.
"There are predictable times of year when we know there are going to be more infants being born, and we hope that in the future this information will be used to help control epidemics," she said.
Outbreaks of childhood diseases are often affected by birth seasonality, which is the variation throughout the year of timing and strength of birth pulses.
For years, wildlife disease ecologists have recognized that birth pulses are huge factors in shaping epidemics of various animal diseases. The husband-and-wife team from U-M wanted to answer if the same is true among humans.
In order to study birth pulses, the team digitized monthly birth records for 78 years from each US state along with over 200 data sets from other countries across the Northern Hemisphere. Once the data was obtained, the researchers analyzed the information using a disease transmission model for measles. This enabled them to examine the implications of childhood infections from birth seasonality.
They discovered that the timing and magnitude of seasonal birth pulses could cause a significant alteration in the magnitude of a measles epidemic.
Often measles is spread at schools where children are gathered in groups and swap germs. According to this new study by Martinez-Bakker and Bakker, unvaccinated infants have a huge impact on disease transmission years before they are in school and potentially worsen a measles epidemic.
The World Health Organization conducts one-a-year campaigns in Africa, the eastern Mediterranean and Southeast Asia. Public health officials could use this new information regarding birth seasonality to provide insight that would optimize these massive vaccination efforts. According to the researchers, it would be extremely beneficial to adjust the campaigns to include babies recently added to the population.
Since the early 1800s demographers have recognized that the number of human births will vary from season to season. Early studies of vital statistics in the United States developed a national-level seasonal pattern of births. It was found that the fewest number of births occur in the spring and the most births occur in the autumn. Studies over the following decades elaborated on this theory and identified other factors to explain these patterns such as income, culture, race, holidays, rainfall, cold winters and the seasonally variable quality of sperm. Despite these factors, no single cause of birth seasonality has been discovered.
Recently Bakker procured access to long-term birth records from over 70 African and Southeast Asian countries. Bakker explained that patterns in birth peaks and their effect on childhood infections should be easy to identify in the African data since there is a high level of seasonal birth pulses and many common endemic childhood diseases. This study is published online in the April 1, 2014 journal Proceedings of the Royal Society B.