MONTREAL -- A circuit-breaker lockdown is in store for Quebec—Premier François Legault made it official in an announcement Tuesday afternoon.

Epidemiologists have been calling for this measure for weeks as Quebec’s COVID-19 caseload and deaths rise.

However, all circuit-breakers are not created equal, they say—there are key ingredients to making one work, and Quebec doesn’t seem to have those lined up.

Dr. Matthew Oughton, an infectious diseases specialist at McGill University, spoke to CTV News about what makes a lockdown effective and what Quebec is still missing.

WHAT’S A CIRCUIT-BREAKER?

The point of a short-term lockdown is to do “a full-court press” on COVID-19, said Oughton. “Control this disease, get it down to zero or as close to zero as we can.”

It’s when you “try to do everything you can to massively interrupt transition in every sector of society all at once,” he said—schools, businesses, workplaces, everything possible.

Many people living in the ever-lengthening red zone may understand the logic after having their onetime “28-day challenge” extended twice already.

“To the average citizen, it kind of feels like we're just dragging on and on and there's no end goal in sight,” said Oughton.

“What we've been doing in this province since Oct. 1, all we're doing is more or less maintaining the status quo.”

One urgent reason for doing a short-term lockdown is to relieve the health system, especially going into the winter, he said. Picture hospitals as “a room filling up with water… that breathing space is getting less and less,” he said. Quebec is pushing its limits right now, he said.

One thing that makes a circuit-breaker work is when people can prepare to stick it out—which Quebec is doing with its advance announcement.

People "might want to stock up ahead of that, [have] lead time to prepare themselves," Oughton said.

But that’s not the only important thing.

HOW LONG DOES A CIRCUIT-BREAKER NEED TO BE?

That depends, Oughton said, but the short answer is three weeks -- just slightly longer than Quebec is planning with its 18-day shutdown.

Why is this? On one hand, the American CDC, the Centers for Disease Control, “recently reduced its isolation period for exposures to 10 days,” Oughton told CTV, down from 14 days.

That’s because it’s clear now that there’s a very low chance someone will be infectious—only about a 1 per cent chance—between the 10th and 14th day after a potential infection, he said. (It’s often specified that if people develop symptoms, they can be infecious for longer.)

However, Oughton said, you should stack two of those incubation periods back to back so that people don’t risk infecting each other again right at the tail end of the first period. 

“So if you follow the CDC approach, you could argue for a three-week lockdown, or a four-week lockdown if you wanted to have an extra margin of safety,” he said.

Legault had originally hinted the lockdown would be two weeks long, which Oughton said would be "too short”—with one exception.

“The only way two weeks would make sense is incorporating some kind of test towards the end of that period,” Oughton said. 

If Quebec were planning to do a huge testing effort across society, testing many asymptomatic people, containing the measures to under three weeks could make sense.

WHY IS TESTING SO KEY IF PEOPLE ARE ALREADY SELF-ISOLATING?

“Essentially, we're flying blind or close to it” in the second wave, said Oughton.

“In something like two thirds of new community cases, they have no established epidemiological links,” not just in Quebec but in most of Canada—in other words, most people never learn where they caught COVID-19. 

An important part of a circuit-breaker is getting a handle on where and how the disease is circulating so that you catch asymptomatic cases and leave the circuit-breaker armed with new data.

However, while Quebec has been talking about getting rapid tests, it’s not prepared to launch a widespread testing campaign in January, Oughton said.

“We don’t have the resources,” he said, whether enough rapid tests or very widespread regular swabbing. 

The Quebec health ministry hasn’t responded to a request from CTV News about its testing plans for the circuit-breaker or the status of the rapid tests it’s been trying to obtain.

While Laval announced recently it will provide at-home saliva tests to schoolchildren, a spokesperson from the Laval health authority told CTV News that while those saliva tests are just as accurate as nasal swab tests, they’re not considered the be the same as rapid tests.

THE PROVINCE RESPONDS

In their Tuesday announcement, provincial leaders said they had tried to strike a balance with their two-and-a-half week plan.

"We discussed many scenarios," Legault said. "We're coming with an average of two weeks and a half... I think that it's enough to curb the [spread]."

When asked what would happen on Jan. 11 if the caseload hadn't gone down, Health Minister Christian Dube said that was too hypothetical for him to answer.

But he said that increasing strictness in the past couple of weeks, including around shopping, seem to be making a small difference in the current caseload, so he believes the 18-day period will be effective.

Public Health Director Dr. Horacio Arruda said bluntly that "I think we cannot afford being confined for months," partly for people's mental states.

The three weren't asked about testing plans during the press conference.