A Nevada County school was closed Tuesday after an unvaccinated student was diagnosed with measles, public health officials said.

The child had recently traveled overseas and became sick after returning to the United States, according to the California Department of Public Health. Local public health investigators are now tracking anyone who came in contact with the child, including schoolmates who also are unvaccinated.

Nevada County, northeast of Sacramento, has among the lowest vaccination rates in California, with only 77 percent of incoming kindergarten students fully vaccinated for the start of the 2015-16 school year, according to state reports.

The child attends Yuba River Charter School near Nevada City, where only 43 percent of kindergarten students are fully vaccinated.

The school was expected to reopen Wednesday. But the Nevada County Public Health Department sent a message to parents that children who were not vaccinated will not be able to attend classes for at least two weeks to be sure they do not get not infected. These children should remain quarantined at home in the interim, officials said.

The child who was diagnosed with measles was last at the school on March 17 and was symptomatic that day.

Last year, California experienced its largest measles outbreak in 15 years, since the disease was declared eliminated from regular circulation in the United States. That outbreak, which infected about 130 people, started at two Disney theme parks in Southern California and quickly spread up and down the state, fueled in large part by pockets of undervaccinated children in many communities.

The outbreak — along with several other, smaller clumps of cases later in the year — prompted legislation making it more difficult for parents to refuse vaccination for their children. The stricter requirements will go into effect for the 2016-17 school year.

Symptoms of measles usually start one to three weeks after exposure and may include high fever, runny nose, coughing, and watery, red eyes. A characteristic rash develops two to four days after the fever. Patients are contagious for several days before and after the rash appears.

Most people with measles will experience mild symptoms for a week or two, but about 20 percent of people develop pneumonia, and 1 or 2 in 1,000 develop encephalitis or die. The measles vaccine is considered 95 to 99 percent effective in preventing illness.

Erin Allday is a San Francisco Chronicle staff writer. Email: eallday@sfchronicle.com Twitter: @ErinAllday