Ottawa health officials say they'll be keeping unvaccinated children and those with incomplete vaccinations who have been exposed to three measles cases out of school until they're fully protected.

The three related cases are in Ottawa and Lanark County and were confirmed on Sunday by an Ottawa Public Health spokeswoman to involve at least one child and one adult.

The cases are now being investigated by OPH and the Leeds, Grenville and Lanark District Health Unit.

All three were either unvaccinated or had not received all of their measles vaccines, the City of Ottawa said in a release.

Dr. Carolyn Pim, OPH's associate medical officer of health, told CBC News on Sunday that the measures were being taken to keep local schools free of the disease.

"We certainly may identify other schoolchildren, but we will deal with those on a one-on-one basis," said Pim.

"We have no particular schools in which there are cases of measles. We don't have any particular schools that we feel are at risk. But by excluding individuals that have been exposed, we're trying to prevent the introduction of any cases into those schools."

Symptoms include fever, cough, blotchy rash

The measles virus is spread through coughing and sneezing and can lead to ear infections, pneumonia, brain swelling or even death.

Common symptoms include fever, cough, runny nose or red eyes and a red blotchy rash that appears several days after the fever starts.

One of the locations where health officials say people may have been exposed to the measles virus is the Children's Hospital of Eastern Ontario, where Ryan Knuth's two-month-old son Theo recently spent five days after developing a fever.

If you decide not to vaccinate your child, it's affecting others. - Ryan Knuth, parent

OPH called Knuth on Friday to let him know that Theo — who is too young to be fully immunized against measles — may have been exposed to the measles virus.

Knuth told CBC News he felt "concern, anger [and] confusion" after getting that call. His son has now received immunoglobulin shots in the hopes the antibodies will offer additional protection, he said.

"If you decide not to vaccinate your child, it's affecting others. And it can and will affect others," Knuth said. Right now, my son is at home, at risk of severe complications — potentially even death — because of exposure to measles."

Measles vaccine 'very effective'

Health officials have not identified the ages of the three people who fell sick, how they might have contracted the virus, or why they were not fully immunized.

Those who have been exposed to measles and have been fully vaccinated, however, have an extremely low chance of becoming ill, Pim said.

"We've identified where the cases who've had measles went, and that certainly is where people may be at risk," said Pim.

Dr. Carolyn Pim says that the risk of contracting measles is "extremely low" for people who've received all of their measles vaccines. (CBC)

"[But] if people are fully immunized, their risk is extremely low. The measles vaccine is very effective. If you've had two doses of vaccine it's virtually 100 per cent effective."

The last measles outbreak in Ottawa occurred in 2014, said Pim. Most of the cases seen in Ottawa are "related to international travel," she said.

The measles vaccination rate among local school-aged children is 98.4 per cent, said Pim, "which is really excellent."

If someone suspects they, or someone in their family, has the measles, they should contact their health care provider, health officials said. The public is reminded to call ahead before coming in.

"It is very important that you ensure your measles immunization is up-to-date. Please remember to report to public health every time your child is vaccinated," the city's press release said.

Possible exposure locations:

The Children's Hospital of Eastern Ontario (CHEO), 401 Smyth Rd, Ottawa

Emergency Room: August 22, 2016, 2 p.m. to August 23, 2016, 2:30 a.m.

Inpatient Ward 4 East: August 23, 2016, midnight to August 23, 2016, 11:59 p.m., August 25, 2016, 8 a.m. to August 28, 2016, 8 p.m.

The Ottawa Hospital (General Campus), 501 Smyth Road, Ottawa

Emergency Room: August 23, 2016, noon to August 24, 2016,1 a.m.

Module G: August 26, 2016, 9 a.m. to noon

Carleton Place Hospital, 211 Lake Ave E, Carleton Place

September 1, 2016,8:30 a.m. to noon

Carlingwood Shopping Centre, 2121 Carling Ave, Ottawa

August 31, 2016, 1 to 6 p.m.

Kanata Superstore, 760 Eagleson Road, Kanata

August 31, 2016, 6:30 to 9:30 p.m.

The Lone Star Restaurant, 4048 Carling Ave, Kanata

August 31, 2016 at 5 to 8 p.m.

Anyone who thinks they may have been exposed can contact their public health unit: