Among those who have been infected recently are a newborn and seven pregnant women, Public Health Ontario says.
Ontario is reporting 195 new cases of measles over the past two weeks in the worst outbreak since the highly infectious disease was considered eradicated in 1989.
Those cases, reported by 11 public health units across the province, bring the total number of cases since the outbreak began last fall to 372: 277 confirmed and 95 probable. That more than triples the case count in Ontario since the last report from Public Health Ontario just two weeks ago.
Between 2013 and 2023, there were a total of 101 measles cases in the province. There have been no recent cases of measles reported in Ottawa.
Among those who have been infected in the widening outbreak are a newborn and seven pregnant women, PHO said.
In the update released Thursday, PHO said the sharp increase in both cases and geographic spread in recent weeks was attributable to ongoing transmission and exposures among individuals who were unimmunized. The vast majority of cases are among those born after 1970.
Since the outbreak began last fall, 31 people in Ontario have required hospitalization, 27 of whom were children. One of those children required intensive care. Thirty of the patients who required hospitalization were unimmunized.
Of the seven pregnant women infected by measles, five were unimmunized. Two had previously received two doses of measles vaccine, PHO said. A measles infection during pregnancy can lead to miscarriage, premature birth and low birth weight.
The outbreak was originally centred in southern Ontario, but in recent weeks it has spread to Eastern Ontario, with nine cases confirmed in Hastings County, north of Kingston. Cases have also be reported in the North Bay Parry Sound District Health Unit and Niagara Region, in addition to southwestern Ontario and Grey Bruce.
Evening Update
There have been no deaths reported in the current outbreak.
The outbreak comes as concerns grow about waning immunization rates, which have dropped significantly since before the COVID-19 pandemic.
Public Health Ontario has reported 70 per cent of seven year olds in the 2023-2024 school year had up-to-date immunization records. In Ottawa, the rate was 64 per cent. Rates in the mid to high 90s are needed to prevent outbreaks.
Ninety per cent of people who are not immunized will get infected if exposed to measles, which can remain in the air for hours after an infected person has left a room.
Health officials say Ontario’s lack of a real-time, integrated vaccination registry is making it more difficult for public health officials to understand the risk and to prevent the spread of measles because available figures are out of date and are likely inaccurate.
Ontario’s outbreak comes at a time of rising measles cases globally. The United States is experiencing a large and growing outbreak.
Earlier this month, Canada’s Chief Public Health Officer, Dr. Theresa Tam, issued a statement urging people to get vaccinated and to take precautions when travelling.
Among that advice is that infants between six months and one year who travel to high-risk areas should receive an early dose of measles vaccine, which is usually given around one year. Tam also advised that children and adolescents should receive both doses of vaccine, as do adults born in 1970 or later (who may have only received one vaccine as a child). Those born before 1970 should receive one dose if they are not immune.
“Immunization is the most effective way to protect yourself and those around you against measles and, we strongly encourage everyone, especially those travelling to areas where a measles outbreak has occurred, to be up to date with their immunizations,” said Ria Yadav, spokesperson for the Ontario Ministry of Health. “One dose of a measles-containing vaccine given after 12 months of age is up to 95 per cent effective at preventing measles. Having two doses is about 99 per cent effective.”
Yadav said a second dose of vaccine may be recommended for adults who are at high risk of being exposed or of exposing others, including those planning to travel to high-risk areas.
More information is available online at the ontario.ca/page/about-measles webpage.
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