(NewsNation) — Two additional cases of measles have been reported inside a Chicago migrant shelter, bringing the total number of cases among residents to four since Friday.

The two new cases were found to be in adults after the first two cases involved children, including one who remains hospitalized in good condition, the city health department announced.

On Monday, the Chicago Department of Public Health said that two additional confirmed cases have been detected at the shelter in the city’s Pilsen neighborhood, where more than 1,800 migrants — including 95 children 2 years of age or younger — are being housed.

A team from the Centers For Disease Control and Prevention will travel to Chicago on Tuesday to help address rising concerns that more measles cases could be coming to a migrant shelter.

A CDC official told NewsNation that team members will work to identify potential exposures and sources of the possible transmission to better understand who may be at risk.

City health officials said Monday that nearly all of the shelter’s residents were assessed by local medical professionals over the weekend and successfully vaccinated more than 900 residents in an operation Chicago Department of Public Health Commissioner Olusimbo ‘Simbo’ Ige called a “massive effort.”

Providing migrants with vaccines

The CDC team that is expected to arrive on Tuesday will also be assigned to provide clinical guidance for the active measles case and to determine the immunity status of those who may have been exposed, the official said.

The CDC announcement was made two days after Chicago Ald. Byron Sigcho-Lopez (25^th Ward) sent a letter to Illinois Gov. J.B. Pritzker imploring the state and federal government to provide immediate help to the city. Sigcho-Lopez said he became aware of the first confirmed case of the measles on Friday morning.

Sigcho-Lopez visited the shelter on Monday and said that city health officials are working with medical teams to vaccinate the remaining 13% of shelter residents who have not yet provided proof of vaccination.

The CDC official said that the agency has provided vaccines to the Chicago Department of Public Health and neighboring communities so they will have enough vaccines for both children and adults.

City health officials found more than 700 shelter residents were immune from measles due to previous vaccinations or infections. The newly vaccinated residents will need to remain at the shelter for 21 days, officials said.

Sigcho-Lopez told NewsNation last week that his letter to the governor would push for immediate vaccinations for children to help “prevent cases like this.” He called for migrants to undergo health screenings after they arrived at the city’s landing zone after being bused from Texas by Gov. Greg Abbott.

In his letter to Pritzker, the alderman wrote that historically, communities of color experience a lower rate of vaccinations due to generational systematic barriers, in many instances not aided or even exacerbated by government-run institutions.

“The politicization of this issue that is a public health matter is troubling and dangerous,” Sigcho-Lopez told NewsNation last week.

He added: “We have to follow the law for everyone. This is a matter of public health. I understand it’s election season, but we have a responsibility because this stigmatization and xenophobia is causing some serious issues of violence.”

A spokesman for Pritzker did not respond to a request for comment on the letter on Monday.

‘Inhumane’ migrant shelter conditions

Migrants staying at the shelter — the largest in the city, according to Sigcho-Lopez — characterized conditions at the facility as “inhumane.” In December, a juvenile died at the migrant shelter, where local officials have been working to improve conditions.

Volunteers who work and live at the facility have ongoing concerns inside the shelter as well, according to a report from NewsNation affiliate WGN,

“It’s very crowded,” a 34-year-old Venezuelan father of two who asked not to be identified told WGN. “There’s too many people in there. The conditions inside of the shelter are inhumane.”

Sigcho-Lopez told NewsNation that his office had set a goal to get the shelter’s population under 1,000 residents. But he said the biggest challenge is determining who is vaccinated and making sure that those who are not vaccinated can be isolated while they await shots.

In an update posted to the Ward 25 website on Monday, Sigcho-Lopez called for all migrants vaccinated after Friday to quarantine at the shelter for three weeks.

The recommendation comes as residents of city-run shelters face a Saturday eviction deadline issued by Chicago Mayor Brandon Johnson.

Johnson had twice delayed the deadline due to cold temperatures but has not moved the March 16 date to rehouse migrants. A spokesman for the mayor did not respond to an email seeking comment on the upcoming deadline.

How serious is measles in crowded spaces?

Dr. David Nguyen, an infectious disease specialist at Rush University Medical Center in Chicago, said that the crowded nature of the migrant shelter is not as much of a factor in the spread of measles as the level of susceptibility of those who are not vaccinated.

He said the virus is “more than a cold or a rash” and can be very severe to those who are susceptible – especially young children and pregnant women. The disease can often be accompanied by complications, Nguyen said, including patients becoming more susceptible to other viruses for weeks or even months after contracting the disease.

He said that typically, the first few days of measles mimic cold symptoms (cough, fever, reddened eyes), but that a week or ten days can pass before the rash that people often link to measles surfaces. Nguyen said that the incubation period for the disease is typically anywhere between 10-14 days – a lag time that he says makes it difficult to get ahead of the virus.

Knowing one’s vaccination status is also critical, Nguyen said. But determining the medical history of newcomers adds an extra obstacle. Sigcho-Lopez said city officials are working around the clock toward that end.

“Unfortunately for some of the migrants, I don’t always think they know that,” Nguyen told NewsNation. “So that’s a challenging thing.”

Nguyen said that up to 90% of those who are exposed to measles and who are susceptible will get the disease. He said that outside of the United States, the rates of vaccination for measles vary depending on the country.

Between 90 and 95% of those who get vaccinated have lifelong immunity from measles, but because of the level of exposure to the two cases, Nguyen said that getting people vaccinated at the shelter should take top priority.

“Hopefully, the city’s efforts…and all of our combined efforts can help interrupt the spread (of measles),” he said. “But I would not be surprised to see more cases.”