All of the cases were reported in individuals who had no immunity to the measles virus, the Philadelphia Department of Public Health spokesperson, James Garrow, confirmed.

The outbreak began when a person who contracted measles outside the United States visited the Children's Hospital of Philadelphia in early December. This individual unknowingly exposed three people at the hospital, who later tested positive for the highly contagious virus. Disturbingly, one of the people exposed at the hospital attended a Philadelphia day care, leading to two children from the facility being hospitalized with measles just days later.

The Philadelphia Department of Public Health released a statement acknowledging the measles case at the day care facility, which occurred on December 20 and 21 and potentially exposed both children and staff members. As of Monday, it has been confirmed that a total of four people in the day care and three individuals exposed at the hospital have been diagnosed with measles, bringing the overall count to eight cases in Philadelphia.

In response to the widening outbreak, the health department has expanded its list of possible exposure locations and dates, which range from December 19 to January 3. Authorities are urging anyone who may have been exposed to self-quarantine for a period of 21 days following exposure.

Health experts emphasize the importance of staying home during this time, given the highly contagious and airborne nature of measles. Dr. Christina Johns, a Maryland-based pediatric emergency physician, highlights the need for vaccination to prevent the infection and potential complications. The department is offering free measles, mumps, and rubella vaccinations for all residents of Philadelphia.

Routine vaccination is highly recommended for children, with two doses being the standard protocol to achieve maximum effectiveness. The first dose is typically administered between 12 and 15 months of age, followed by a second dose between 4 and 6 years old. Vaccination has shown approximately 97% effectiveness in preventing measles.

Measles is easily transmitted through respiratory droplets, remaining in the air for up to two hours after an infected person has left a room. In addition, the virus can be spread by touching contaminated objects or surfaces. Initial symptoms resemble those of common respiratory illnesses and are eventually followed by a distinctive rash that starts on the face and spreads downwards within three to five days.

Though measles was declared eliminated in the United States, outbreaks can occur when unvaccinated individuals travel to countries where the disease is still prevalent and bring it back with them. This underscores the importance of maintaining high vaccination rates to protect vulnerable members of the population.

Measles outbreaks serve as a "call to action" to ensure communities are up-to-date on their vaccinations, according to Dr. Johns. She warns of potential complications, including blindness and encephalitis, associated with measles, emphasizing the significance of preventing vaccine-preventable diseases.

While the majority of US children are fully immunized against measles, mumps, and rubella, with a reported vaccination rate of 92% by age 2, it remains crucial to remain vigilant in maintaining these rates to prevent the resurgence of vaccine-preventable diseases.

In 2023, there were 48 reported cases of measles in the United States. Prior to the measles vaccination program, millions of people contracted the virus each year, resulting in hundreds of deaths.

The most recent significant measles outbreak occurred in 2018-19 in Rockland County, New York, primarily affecting unvaccinated children in Orthodox Jewish communities.