What you need to know about measles after Ohio outbreak sickens 19 children

Already facing a challenging respiratory season, pediatricians in Ohio are now dealing with another foe: measles.

According to statistics provided to ABC News by the Columbus Public Health Department (CPHD), as of Tuesday afternoon, 19 children have contracted the virus.

Nearly half of these children were hospitalized due to severe symptoms of the infection. Almost half were under five years old.

The rate of children requiring hospitalization during this outbreak was nearly double what's typically seen during measles outbreaks, Dr. Matthew Washam, pediatrician and chief of epidemiology at Nationwide Children's Hospital in Columbus, told ABC News.

The Centers for Disease Control and Prevention told ABC News that it is deploying a team to Ohio to assist with mitigating the outbreak.

Here's what to know about the outbreak, why these rare cases occur and how Americans can protect themselves against the virus.

Is measles serious?

Measles is a very contagious disease with the CDC saying every individual infected by the virus can spread it to up to 10 close contacts, if they are unprotected including not wearing a mask or not being vaccinated.

Complications from measles can be relatively benign, like rashes, or they can be much more severe, like viral sepsis, pneumonia, or brain swelling.

"The impression that measles is a trivial infection akin to the common cold with a rash, that is incorrect," Dr. William Schaffner, a professor of preventive medicine and infectious diseases specialist at Vanderbilt University Medical Center, told ABC News. "Measles is a very nasty virus."

"Before we had the measles vaccine in the United States, 400 to 500 children died of measles and its complications each and every year. So, measles can make you very, very sick," he continued.

Am I protected from measles?

The CDC says anybody who either had measles at some point in their life or who has received two doses of the MMR (measles, mumps, rubella) vaccine is protected against measles.

One dose of the measles vaccine is 93% effective at preventing infection if exposed to the virus. Two doses are 97% effective.

Schaffner said there is no reason for anyone who has been vaccinated to receive a booster dose when isolated outbreaks occur.

"If you've had those two doses of the measles vaccine, you're protected essentially for life," he said.

In 2000, measles was declared eradicated from the U.S. thanks to the highly effective vaccination campaign.

Why did this outbreak occur?

The CDC team deploying to Ohio will also assist with investigating the outbreak's origins, given that children across 12 schools/daycares have contracted the virus so far.

The fact that these infections occurred over a two-week timespan is throwing another wrench in efforts to track down the outbreak's origins.

Recent research from the World Health Organization described the "largest continued backslide in vaccinations in three decades" due to missed routine care during the pandemic.

In the U.S., a May study found one-third of American parents reported a child with a missed vaccination due to barriers imposed by the COVID-19 pandemic.

However, according to Kelli Newman, director in the CPHD Office of Public Affairs and Communications, "our investigation so far points to vaccine hesitancy and choosing not to be vaccinated" as the driver for the outbreak.

What is vaccine hesitancy?

Vaccine hesitancy is defined as delaying or refusing vaccination despite their widespread availability.

Accordingly, CPHD's conclusion so far fits with a troublesome trend sweeping the United States -- and beyond.

Even before the pandemic, reluctance around getting vaccines was hitting a fever pitch. Vaccine hesitancy was named one of the top 10 threats to global health by the WHO in 2019.

In the U.S., vaccine hesitancy has been further stoked by politics.

A study by the Colorado Health Institute, a non-partisan research organization, found that COVID vaccination rates across the state were strongly correlated with counties' political beliefs.

The MMR vaccine has been especially targeted by the vaccine hesitant community. Much of the controversy around the vaccine derives from a now retracted and discredited 1998 study from The Lancet that falsely drew a connection between the shot and rates of autism.

How can we encourage vaccination?

Despite research debunking the Lancet paper, many communities continue to grapple with misinformation around the MMR vaccine.

"Misinformation and disinformation related to vaccines continues and persists," Washam told ABC News. "These are not conversations that can be had in five or 10 minutes or in a single visit."

In Ohio, the health department has tried to combat this misinformation by offering walk-in MMR vaccine appointments that include one-to-one counseling with health providers.

Fortunately, despite the increasing frequency of measles outbreaks, vaccine hesitancy still remains the exception rather than the rule. CDC data shows that more than 90% of children were vaccinated against MMR by the age of two. By 17 years old, that share rises to 92%.

However, epidemiologists worry a 10% unvaccinated rate in children is the bare minimum required to stem future outbreaks. They are even more concerned about communities, like that in Ohio, where the vaccination rate is even lower.

"That 90% is not evenly distributed across the country -- there are pockets of under vaccinated areas, and those are the areas that are susceptible," Washam told ABC News. "Measles anywhere in the world is a risk for measles everywhere in the world."

Schaffner said it is important for local public health authorities to bring trusted leaders, be they political or religious, to speak about the importance of vaccination.

"They can provide them not only information, but a sense of reassurance, a sense of comfort, letting them know that it is the appropriate thing to do for their own children's benefit, but also for the benefit of the entire community."

Additionally, this winter amid a so-called "tripledemic" of flu, RSV and COVID-19, experts are urging families to ensure their children are vaccinated against the flu to reduce the burden on health systems and prevent any undue harm. Vaccination rates for the flu historically hover around 60%.

"Some families say, I'm going to wait until X or Y or Z date to get the vaccine," Washam told ABC News. "Well, this might be the year to get it a little sooner."

ABC News' Youri Benadjoud and Faith Crittenden contributed to this report.