Unvaccinated infants fueling disease epidemics, researchers say

A patient receiving the measles vaccine. (REUTERS/Valentin Flauraud)

Measles: A highly contagious respiratory virus thought to be eradicated in America.

Epidemics of the measles virus still pose a threat to children worldwide – but due to the recent anti-vaccine movement, the virus is making a comeback in the United States as well.

As a result, a husband-and-wife research team from the University of Michigan is strategizing ways to improve vaccination campaign strategies – and they believe one interesting set of data could help: seasonal birth rates.

Micaela Martinez-Bakker and Kevin Bakker, both of the University of Michigan’s department of ecology and evolutionary biology, set out to analyze seasonal birth rates throughout the Northern hemisphere in an attempt to identify ‘birth pulses’ – times when more infants are born in certain populations.

“In developing countries, to get children vaccinated, many have to rely on national vaccination campaigns, and those happen once a year, and they have to vaccinate as many infants as they can,” Martinez-Bakker said.  “…If you know the time of the birth pulse, vaccination campaigns can use that information to determine when there are large numbers of infants in the population, and when they should vaccinate. It’s getting the most bang for your buck in terms of vaccinating if you can only go out once year.”

Utilizing 78 years of monthly birth records in the U.S., as well as 200 data sets from countries throughout the Northern hemisphere, the researchers were able to pinpoint seasonal birth pulses in various regions across the globe.

“Further away from equator, in Europe, that birth pulse is earlier in the year, between May and August,” Bakker said. “Closer to the equator, in the Caribbean, for example, the birth pulse is much later between September and December. And there are clear patterns across the U.S.: If you live in New York, July or August, or if you live in the South, you’re more likely to have a birth in October and November.”

For their study, published in Proceedings of the Royal Society B, the researchers also analyzed how seasonal birth patterns affected rates of disease outbreaks, focusing specifically on the measles epidemic.

“Measles is a virus primarily affecting children, and we were able to show that birth seasonality influences the size and frequency of measles outbreaks as well,” Martinez-Bakker said.

As a result, the researchers theorized that timing vaccination campaigns according to seasonal birth pulses could potentially decrease measles epidemics – as well as outbreaks of other contagious diseases like polio.

Although parents in the U.S. have access to vaccines for children year-round, vaccine campaigns are becoming increasingly important as more parents are choosing not to vaccinate children – a trend that Martinez-Bakker called “deeply disturbing.”  According to the CDC, 189 people in the U.S. contracted the measles in 2013, representing the second largest surge in cases since the disease was “eliminated” in 2000.

“According to the CDC, there were 11 measles outbreaks in the U.S. last year, and all cases were in unvaccinated or unknown vaccine status [individuals],” Martinez-Bakker said. “Essentially, our work has shown that having susceptible infants in the population, or susceptible young children, that’s what allows these large explosive outbreaks to happen. This study is one of many studies that highlights the importance of vaccination and reducing the number of susceptible infants and children in the population.”

Every year, nearly 4 million children under the age of 5 die from vaccine-preventable diseases worldwide – but the researchers hope that better vaccine campaigns could help chip away at this number.

“We hope that the more information that’s out there, the more parents are informed about how these diseases play out in populations,” Martinez-Bakker said. “That that will hopefully be convincing to them that it’s important to vaccinate.”