The fluctuation in the number of births throughout the year, coupled with the rising rate of unvaccinated children, could magnify the impact of a recent measles outbreak in the U.S., according to new research. 

Researchers used birth seasonality—times in the year when there is an influx of newborns—to show how more-aggressive vaccination campaigns can help prevent outbreaks of childhood infectious diseases.

Using 78 years worth of monthly U.S. birth records, wife-and-husband research team Micaela Martinez-Bakker and Kevin Bakker of the University of Michigan's Department of Ecology and Evolutionary Biology found that the regular seasonal rise in births could help trigger an epidemic.

The higher number of births, coupled with the fact that newborns are too young to be vaccinated, is like stacking twigs on top of one another and waiting for a spark, said the researchers, whose work is supported by the National Science Foundation.

“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,” Martinez-Bakker said in a statement. “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.”

Their research was published in the journal Proceedings of the Royal Society B.

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Seasonal Births Used to Adjust Vaccination Schedules

In the U.S., seasonal birth rates vary. In northern states, more babies are born during the spring and summer months, while southern states see an influx in autumn, the researchers found.

Knowing when births will peak in a region can help public-health officials adjust once-a-year vaccination campaigns to better serve each community.

The Bakkers also discovered that unvaccinated infants play a significant role in disease transmission, years before they get older and enter school.

“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,” Martinez-Bakker said.

While measles has been declared eradicated in the U.S., clusters of unvaccinated children and adults are bringing the once-common disease back into the national spotlight. Because it is highly contagious, a person infected with measles—often contracted during travel abroad—can spread the disease rapidly.

Read More: Student Infected with Measles Highlights the Importance of Vaccination »

How Herd Immunity Prevents Epidemics

“Herd immunity” means that at least a 95 percent vaccination rate in the population at large is enough to prevent highly contagious diseases like measles from taking hold.

One of the best examples of herd immunity appeared this year in the San Francisco Bay Area, when an unvaccinated college student contracted measles abroad. The student used the area’s largest public transportation system for three days during peak commute hours, potentially exposing thousands of people to the virus.

Public health officials found no new cases of measles after the student was identified, and they attributed the lack of a public-health emergency to high rates of vaccination in the community.

Learn How the Anti-Vaccination Movement Caused Another Deadly Year »

Anti-Vaccination Groups Continue Campaigns

With celebrity anti-vaccination advocates like Jenny McCarthy and Kristin Cavallari continuing to push the results of faulty, long-debunked research that claimed the MMR vaccine (which guards against measles, mumps, and rubella) causes autism, the U.S. is seeing a re-emergence of preventable diseases as more parents opt out of vaccinating their children.

Government vaccination rules apply only to people who want to enroll their children in public schools. Many private schools don’t require the same immunization schedule.  

Conventions such as these have created their own problems, especially in high-population areas with small sects dedicated to non-vaccination. The most common source of preventable disease outbreaks are people who don’t immunize their children for personal or religious reasons. 

British Columbia is currently experiencing its largest outbreak ever, with 320 measles cases tied to a religious group that denounces vaccines, according to The Province.

Read More: 31 Failed Attempts to Loosen School Vaccination Rules »

Outbreaks Spur Crackdown on Vaccine Exemptions

In 2013, the U.S. had the second-highest number of measles cases in 20 years, led by 58 cases stemming from a Brooklyn community of Orthodox Jews.

In 2011, a New York City private school came under heavy fire when only 23 percent of its kindergartners were fully vaccinated. A further review found that 245 New York City private schools fell below the threshold for herd immunity, while public school children were vaccinated at a rate of 98 percent, according to New York Magazine.

Ohio State University is currently experiencing an outbreak of mumps, which is covered with the MMR vaccine. As of Wednesday, 116 reported cases have emerged, with three confirmed cases in students who were not vaccinated against the virus. 

"If even one person is unvaccinated, we are all at risk," Jose Rodriguez, a Columbus, Ohio, health department spokesman told Fox News.

Because many outbreaks are linked to personal-belief exemptions, many states are cracking down on the reasons parents can give for not protecting their children from preventable diseases.

From 2009 to 2012 there were 36 attempts in 18 states to change immunization requirements, 31 of which intended to expand the scope of exemptions. None of those new exemptions passed, according to a review published in the Journal of the American Medical Association.

So far this year, Colorado and Oregon have adopted legislation to reign in personal and religious exemptions for school vaccinations.