Health officials in Philadelphia are urging members of the public to ensure they’re vaccinated against measles ― and to follow quarantine orders if they’re exposed ― amid an outbreak of the extremely contagious virus in the city and surrounding area.

At least eight people had been diagnosed with measles as of Friday, a spokesperson for the city’s Department of Public Health told HuffPost. The number of confirmed cases has held steady since Monday.

“Unfortunately, we are seeing cases of measles that have spread to vulnerable individuals including young children due to people declining vaccination and also failing to adhere to quarantine recommendations,” Philadelphia Health Commissioner Cheryl Bettigole said in a release last week.

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“We are asking all city residents who may have been exposed to measles to do their part to ensure that no additional infants are harmed by this infection,” she said.

The outbreak began in December, when an infected baby was admitted to the Children’s Hospital of Philadelphia, according to The Philadelphia Inquirer. The infant had recently been in a country where measles infections still regularly occur, per the paper, and was admitted to the hospital with a fever but didn’t develop the telltale measles rash until days later.

During the child’s hospital stay, the city said, three other patients who were also not immune to measles ― that is, they hadn’t been vaccinated and hadn’t previously tested positive for the virus — were exposed and later tested positive.

The virus then spread at a day care after a child with a confirmed case of the virus was dropped off on Dec. 20 and 21, disregarding quarantine orders, the city said. At least two children at the day care later tested positive but only after visiting various health care centers in the area, resulting in further community exposure. Shortly after, three more children at the day care also tested positive for measles. Of the five children, two were hospitalized.

All of the hospitalized measles patients have since been released, the city spokesperson told HuffPost.

City officials have released a list of locations where people may have been exposed to the virus on specific days and times.

About 90% of people who have close contact with an infected person will get measles if they are not immune. About 93% of children in Philadelphia are vaccinated against the virus, though it still remains dangerous for immunocompromised people and for infants too young for the shot, the city said.

Of those infected, 1 out of every 20 children will get pneumonia, which is the most common cause of death from measles in young children.

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“Sharing the same airspace with a person infected with measles (same classroom, home, waiting room, airplane, etc.), or being in these areas up to 2 hours after the infectious person has left the area is a measles exposure. Exposure criteria apply even if the infectious person was masked,” the city said.

The city has instructed exposed individuals to quarantine themselves at home for 21 days following exposure. Early symptoms of measles are fever, runny nose, cough and puffy eyes, followed by a rash. Anyone who suspects they may be infected should contact their health care provider before physically going to a public office so that others aren’t potentially exposed.

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