Thirty new cases of mumps this week in Nova Scotia have added to a total of more than 300.

There have been 302 reported cases of the highly contagious disease since the outbreak began in February.

Most of the patients are young adults in their early 20s, and health officials have said the outbreak stems from waning immunity within that age group.

Since the 1990s, the mumps vaccine has come in two doses. But some young people did not return for a second booster or missed vaccination altogether.

Mumps has spread to New Brunswick, Prince Edward Island and Ontario, as out-of-province university students head home.

Mumps causes swollen and tender glands and other flu-like symptoms, but in rare cases can also lead to sterility, deafness and viral meningitis.

The virus is spread by coughing, sneezing, sharing drinks and food, and kissing. It can be contagious for about seven days before symptoms appear, and up to nine days after.

In the Halifax area, as many as 136 hospital workers were on paid leave and in isolation after they tested positive for exposure to mumps.

Health officials in Nova Scotia are making 40,000 doses of a mumps booster available to workers across the province.