Twenty students who have not been vaccinated against the measles are not be allowed on the campus of Huntington Beach High School for three weeks after a possible exposure to the virus, officials confirmed Monday.

A student with measles was on the Orange County campus in early January, and could have potentially spread the highly contagious disease according to a letter sent to parents.

Students who have been exposed and do not have the necessary vaccination to guard against the disease were sent home for three weeks, according to county health officials. They will not be allowed to attend school until Jan. 29, according to the Orange County Department of Education.

Some parents said the district was going overboard.

"I'm not a doctor so I can't say, but that seems extreme to me," one parent said. "I mean, I had the measles and I think I was out for three days."

However Orange County Department of Education Health and Wellness Coordinator Pamela Kahn told NBC4 Tuesday that keeping the students away from school is the only thing they could do to prevent the disease from spreading further.

As carriers are contagious both four days before and four days after developing a rash, and as students could be at school for as long as 21 days before a rash develops, it is essential to keep unvaccinated pupils away from school for that period to minimize the exposure of other students from the disease.

The county has confirmed 16 cases of the disease, among 46 confirmed cases in California.

In late December an outbreak was reported among people who had visited Disneyland, but health officials in San Diego and Orange county have now confirmed the outbreak has spread beyond the initial cases.

Measles is spread through the air or contact with an infected person and is highly contagious.

It is characterized by fever, rash, cough and red, watery eyes.

Doctors advise that anyone who thinks they may be infected call their doctor immediately.

Michael Larkin and Annette Arreola contributed to this report