What we know about measles during pregnancy

The death of an Ontario infant born prematurely and infected with measles through the mother is raising questions about how the virus is transmitted during pregnancy.

On Thursday, Ontario health officials announced the death of a baby who was infected with the virus while in the womb. It was the first fatality in the provincial outbreak that began on Oct. 28 last year and includes 2,009 probable and confirmed cases.

"While measles may have been a contributing factor in both the premature birth and death, the infant also faced other serious medical complications unrelated to the virus," Dr. Kieran Moore, Ontario's chief medical officer of health, said in a statement released Thursday. 

Measles is a respiratory infection with symptoms that include fever, a blotchy rash, a cough and red, watery eyes. In May 2024, a child under five died of measles in Hamilton, but before that, there were no measles deaths in the province in more than a decade.

Moore has previously said the current outbreak was traced to a Mennonite wedding in New Brunswick, and is spreading primarily in Mennonite and Amish communities where vaccination rates lag. The majority of those cases are in southwestern Ontario.

WATCH | Death of a measles-infected baby in Ontario: 

Measles-infected baby dies in southwestern Ontario

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An infant born prematurely and infected with measles in the womb through their mother has died, Ontario's Chief Medical Officer Dr. Kieran Moore announced Thursday. It is the province's first recorded death from the current outbreak that started in October of last year.

Health officials stress that anyone who isn't vaccinated is vulnerable to measles and they encourage everyone to ensure they are up to date on their Measles, Mumps and Rubella (MMR) vaccines. 

"I urge everyone, but especially those who may become pregnant, to ensure they have received two doses of the MMR vaccine, which will protect both a parent and baby," said Moore.

What is known about measles transmission during pregnancy?

Dr. Jacqueline Wong, a pediatric infectious diseases specialist at McMaster Children's Hospital, says transmission of measles during pregnancy is rare.

If the baby does contract measles from the mother in utero, Wong says the impact varies depending on how far along the pregnancy is. 

"Your risk of transmitting the infection to the baby varies during the different trimesters because of the development of the fetus, the development of the placenta and the blood flow."

What are the risks during pregnancy?

Dr. Sheryl Choo, a maternal-fetal medicine specialist at Royal Alexandra Hospital in Edmonton, says there are serious complications that can result if people who are pregnant become infected with measles. 

For instance, she says pregnant people infected with measles can develop lung infections like pneumonia at almost double the rate of those who are not pregnant. 

If people become infected with measles during pregnancy, Choo notes it can also increase the risk of serious complications including miscarriage and premature birth.

According to Moore, the MMR vaccine has been safely used for over 50 years and is highly effective. "Two doses provide nearly 100 per cent protection," he said in a statement Thursday.

What about risks to the baby?

Babies born to those infected with measles can face complications related to premature birth, such as low birth weight and breathing issues, which can result in stays in the neonatal intensive care unit, Choo said. 

This is all on top of the symptoms of a measles infection itself, she said. 

Much rarer complications of measles can include subacute sclerosing panencephalitis, or SSPE. It is almost always fatal and generally develops seven to 10 years after an initial measles infection, even if the person appears to have fully recovered. 

It can be dormant in the brain for years and may eventually flare up, causing brain inflammation and resulting in children or young adults losing the ability to move and speak.

According to the Public Health Agency of Canada, SSPE occurs in between four and 11 out of every 100,000 measles cases.

Health officials say it strikes between seven and 11 years after an initial infection and the highest rates are among children who contract measles before the age of two.

If I'm pregnant can I get the measles vaccine?

No, the measles vaccine is not recommended to be administered to people who are already pregnant. 

"If you want to take the measles vaccine, it has to be before you're pregnant," Choo said.

That's because the measles vaccine contains a live strain that is a weakened form of the virus, which is not recommended during pregnancy. 

Choo says that's because there is a theoretical risk that the measles virus contained in the vaccine can be passed to the baby.  

In contrast, vaccines that contain inactivated viruses can be given during pregnancy. The flu vaccine is one example.

Is there treatment for pregnant people exposed to measles?

If you're pregnant and you think you may have been exposed to measles, health officials advise you to contact your local health authority. They can determine if exposure occurred and direct patients to seek appropriate care without contributing to further spread.

If measles exposure is confirmed, Choo says there is an injectable medication option called IVIg. Depending on when the exposure occurred, the medication may be used to help protect against infection or reduce severity of the illness. 

However, health officials and doctors agree that the best way to protect against measles is immunization. 

"The most important recommendation or advice I can give … is to make sure you're up to date with all the immunization if you're starting that journey of becoming pregnant," Wong said.