With the number of measles cases increasing rapidly in Orange County, Newport-Mesa Unified schools are sending out letters to families that are at risk of contracting the disease, officials said.

The letter encourages families of students who have not been immunized, or who are under-immunized, to get two doses of the MMR (measles, mumps, and rubella) vaccine.

So far, there have been 21 confirmed cases of measles in Orange County this year, the most of any county in the state, with five of the victims being children, according to the Orange County Department of Public Health.

Though Newport-Mesa has not reported any cases, the district is sending the letter as a precaution, said district spokeswoman Laura Boss.

Measles are highly contagious and cause fever, rash, cough and red, watery eyes. The virus spreads by air and through direct contact with an infected person.

There has been a recent downward trend in immunization rates for students in California, including Newport-Mesa Unified, statistics show.

California is one of 20 states that allow parents to justify not vaccinating their children based on personal or religious beliefs.

The district has the third-lowest percentage of immunized kindergarten students, with 83.2% receiving vaccinations, according to the Orange County Health Care Agency's 19th annual report on the Conditions of Children in the county for 2013.

However, health officials say immunization is the best defense against the disease.

— Hannah Fry

@HannahFryTCN