FREDERICTON -- Taxi users are being warned they may have been exposed to the measles virus in Saint John, N.B., through a previous passenger.

Dr. Jennifer Russell, New Brunswick's chief medical officer of health, says someone with a confirmed case of the measles travelled repeatedly by taxi on May 22, 24, 25 and 26.

The person used Vet's Taxi Ltd., and other people using the same cab afterward could have been exposed to the virus for up to two hours, she said.

"Because measles is transmitted by respiratory droplets, those droplets can remain in the air for up to two hours after the person was in that vicinity," she said Friday.

She said anyone who may have been in those cabs won't be offered the vaccine because too much time has passed.

"We are outside the 72-hour window when a dose of the vaccine would be effective to protect those people exposed during those times. We are asking that if you did take the cab, that you are asked to be watching for symptoms of measles," Russell said.

There have been 11 confirmed cases of the measles in New Brunswick -- all in the Saint John area.

Early symptoms of the virus may include fever, cough or tiny white spots in the mouth. Within three to seven days, a red rash will appear, first on the face and then spreading to the body, arms and legs.

Russell said anyone showing symptoms should self-isolate and call the 811 Telecare line to learn what to do.

New Brunswick's first confirmed case involved someone who had travelled outside the province, while the rest were exposed at the emergency department at the Saint John Regional Hospital or at Kennebecasis Valley High School.

Russell said 9,000 doses of the vaccine have been issued to deal specifically with the outbreak.

She said there is no issue securing enough doses of the vaccine if the outbreak continues, and young children aged 12 to 18 months old who are scheduled to be immunized are getting their shots.

However, people not exposed to the virus are having trouble getting a preventative shot.

Paul Blanchard, executive director of the New Brunswick Pharmacists' Association, said local pharmacists have run out of the vaccine and likely won't get more until July.

He said they are fielding lots of inquiries.

"In the Saint John area, on average our members are getting five to six calls an hour with respect to questions about measles," he said Friday.

Blanchard said his biggest concern is misinformation he's seeing online about vaccines that may be convincing some people not to get them.

"I want to encourage people to get their vaccines. It's important for people to get the facts and get vaccinated. It's not just for their own interests. It's also for protecting young children or seniors who are more vulnerable," he said.

On Thursday, U.S. health officials reported 971 measles cases so far this year, the highest tally in 27 years.

They say overall vaccination rates have remained fairly high, but there are outbreaks in communities where parents have refused recommended shots.

Health officials in New Brunswick say they need to count 40 consecutive days without new cases in order to consider the current outbreak over.