The Denton County Health Department says five measles diagnoses there are linked to the 15 that spread through a Tarrant County church earlier this month.
Spokeswoman Sarah McKinney says the five patients are between nine and 17 years old, and all live "in the Justin area."
Justin is about 17 miles from the Eagle Mountain International Church, where health experts said a man spread the viral infection to 10 others. The man, who was visiting the church as part of a mission trip, contracted measles overseas and spread it to congregants, the church said.
The five cases near Justin all involve home-schooled children.
But Mayor Greg Scott said he is still concerned about what could happen when public school classes resume next week.
"We don't know where they had contact, who is in incubation and who isn't," Scott said.
Three school districts in the area, including Northwest ISD, all said they weren't aware of any students contracting the disease ahead of school starting next week.
Students are required to have proper vaccinations, but parents can opt out.
None of the Denton County patients were immunized, according to officials.
In Tarrant County, eight of 11 patients had not been vaccinated. Al Roy, spokesman for the health department there, said Tuesday that the other three claimed to have been, but had no records to prove it.
Nevertheless, the outbreak has health experts reiterating the need for parents to immunize their children. Measles is a viral infection that typically affects the young, however adults are still susceptible to it.
College students, international travelers and health care personnel are especially reminded to be vaccinated if they haven't already been.
“Those who are not currently immunized should re-evaluate the benefits and risks of vaccination, based on the presence of an outbreak," Denton County Health Department Director Bing Burton said in a prepared statement.
There have been 20 cases of measles statewide –– 19 of those are in North Texas. Symptoms include cough, runny nose, inflamed eyes, sore throat, fever and a red, blotchy skin rash. It can be fatal.
The majority of victims who succumb to measles are under five years old.