Breakthrough cases in N.B. show need for regular asymptomatic testing, says doctor

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Dr. Lisa Barrett, an infectious disease researcher and clinician at Dalhousie University, said there will be more breakthrough cases if there's more community spread.  (CBC - image credit)
Dr. Lisa Barrett, an infectious disease researcher and clinician at Dalhousie University, said there will be more breakthrough cases if there's more community spread. (CBC - image credit)

The number of fully vaccinated New Brunswickers who are contracting COVID-19 points to increasing levels of spread in that province and a need for more asymptomatic testing, says an infectious disease expert in Halifax.

Dr. Lisa Barrett, an immunologist at Dalhousie University, spoke with CBC Radio's Maritime Noon about the case of a fully vaccinated city councillor from Saint John, N.B., who had no symptoms and tested positive last Friday.

David Hickey learned he had COVID-19 after receiving a rapid test at the P.E.I. border where he was travelling for a weekend getaway. A PCR test later confirmed the positive result.

New Brunswick announced 75 new cases of the virus on Monday, 22 of them linked to people who are fully vaccinated. As of Monday there were also 49 people in hospital in that province, eight of whom are fully vaccinated.

"I don't want people to assume that this means that vaccines don't work. This is somewhat expected," Barrett said Tuesday.

New Brunswick has been dealing with record case counts — and now has more than 760 known active cases — after initially dropping public-health restrictions in July.

"The percentage of virus in the community is higher right now in that area, and that's why ... you're going to see more absolute numbers of people because of those higher percentages in the community," Barrett said.

Jacques Poitras/CBC
Jacques Poitras/CBC

In Nova Scotia, 90 per cent of the COVID-19 cases since March involved unvaccinated people, just over six per cent involved partially vaccinated people and 3.8 per cent were fully vaccinated.

Hickey is now isolating and said he's feeling fine. He wanted to speak out about his experience to urge others to get vaccinated so they can reduce their chances of getting seriously sick and ending up in the hospital.

"The number of symptoms you have if you're fully vaccinated tends to be a lot lower and your ability to transmit or infect somebody else is lower, but it's certainly not zero," Barrett said.

Why didn't initial testing catch the case?

Before Hickey left for his trip last week he took two rapid tests in New Brunswick and both were negative.

Barrett said rapid tests aren't as sensitive as PCR tests in picking up low levels of the virus, and that's why it's important to use the tests regularly.

"Does it say the test doesn't work? No. It does speak, however, to the fact that infections — after you've been exposed— take a little while to set up in your respiratory tract, and the level of virus has to be high enough for any test to pick up," she said.

She urged people and provincial governments to continue to provide asymptomatic tests to people a couple of times a week, especially as fourth waves of the pandemic hit many parts of the country.

"During a wave when virus is high is when you need this kind of testing to keep the community virus levels down without locking down," she said.

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