The Board of Health said on Wednesday that a public health emergency mandating that nearly every person in a heavily Orthodox Jewish neighborhood get vaccinated for measles will remain in place for the time being.

It is unclear how long the mandate will remain in effect.

Mayor Bill de Blasio declared the emergency last week over a measles outbreak that has sickened more than 300 people since it began last October, with nearly 50 percent of those infected being children between 1 and 4 years old. The city says no one has died from the outbreak, but more than 20 people have been hospitalized.

In an effort to contain its spread, the mayor's office has required every person older than six months in the zip codes 11205, 11206, 11211, and 11249 — all in Williamsburg — to receive the measles vaccine. The order applies to anyone living, working, or going to school in the area.

The city's Department of Health and Mental Hygiene will review vaccination records of every person who may have been in contact with measles patients, and de Blasio says anyone who is not vaccinated could be fined $1,000. The health commissioner said on Wednesday that no one has been fined to this point because the point of the order is to encourage vaccinations, not to collect money.

The city has said it would help everyone covered by the order get the vaccine if they can't get it quickly through their regular medical provider.

A lawsuit challenging the city's emergency order was filed by a group of parents. A hearing will be held Thursday.

Health officials say 16,000 measles vaccines have been administered since their active order, but cases are still spreading. More than 3,300 kids in Williamsburg have not been vaccinated.

The city has already ordered religious schools and day care programs serving Williamsburg to exclude unvaccinated students or risk being closed down. 

One child care program in Williamsburg was shut down Monday after the Health Department said the program failed to provide vaccination records.

Medical experts almost unilaterally concur that the vaccines are safe and do not cause autism. The city notes that nine CDC-funded or conducted studies since 2003 have found no link between the vaccines and autism spectrum disorder.