An outbreak of pertussis, also known as whooping cough, has doubled in New Brunswick since last month.

So far this year, 892 people have been diagnosed with whooping cough in the province. The largest cluster – 45 per cent – is in Health Region 1, which includes the Moncton area.

The outbreak crossed the border into Cumberland County, Nova Scotia. A few cases were reported there at the beginning of June.

"The good news for us is it hasn't continued," said Dr. Frank Atherton, the assistant medical officer of health for Nova Scotia.

Whooping cough leads to a dry, rough cough in adults, and can be fatal in babies and children. Whooping cough is easily transmitted from person to person. Atherton said immunization is the key.

"We need to make sure all of our children, particularly, and adults are immunized against pertussis. It's a nasty disease."

New Brunswick began a vaccination campaign in May when the outbreak began. Thousands of students in Moncton and Saint John were given shots before the end of the school year. The province plans on vaccinating even more children when classes begin again in the fall.

In 2009, there were just 15 cases of pertussis reported in New Brunswick.