(NewsNation) — At least eight people have been diagnosed with measles in an outbreak that started last month in the Philadelphia area — the two most recent cases were confirmed on Monday.

The Philadelphia Department of Public Health (PDPH) reports seven cases were discovered in Philadelphia and another incident from outside the city.

The outbreak started after a child, who’d spent time in another country, was admitted to the Children’s Hospital of Philadelphia (CHOP) with an infection, later identified as measles. The PDPH considers the case to be “imported” but did not say from where.

The disease spread to three other people at CHOP, two of whom were already hospitalized for other reasons.

Two of those infected at the hospital were a parent and a child. The child wasn’t vaccinated and the parent was offered medication usually given to unvaccinated people that can prevent infection after exposure to measles, but refused, The Philadelphia Inquirer reported.

Despite instruction to quarantine, the child was sent to daycare on Dec. 20 and 21, the health department said. Four more people got infected at the Multicultural Education Station.

The health department said none of the people who’ve been diagnosed were immune to measles. Officials did not release specifics about the patients’ ages or vaccination status.

In addition to the two who were already hospitalized, four people were admitted to the hospital, the health department said.

Health officials warn the virus is extremely contagious for people who aren’t vaccinated. An infected person can infect up to 90% of people they’re exposed to if they those contacts aren’t immune.

People can remain contagious for about eight days — four days before the disease’s signature rash appears and four days after, according to the Centers for Disease Control and Prevention. The virus can also survive up to two hours in the air after an infected person leaves the area.