Quebec's early March break contributed to province's spring woes, study suggests

COVID-19 could have been carried to Quebec by as few as 247 people coming home from travelling, according to a new genome sequencing study conducted by the Institut national de santé publique du Québec (INSPQ) and the McGill Genome Center. 

The study looked at the genome sequences of 734 COVID-19 samples in Quebec between mid-February and April 1 and compared them to over 21,000 other samples elsewhere in the world.

In Quebec, the first confirmed case of COVID-19 was traced back to as early as Feb. 25, according to the study, but it and other early cases were well contained, and did not lead to sustained transmission.

"It was a trickle at first," said Jesse Shapiro, a professor in the department for human genetics and head of genome sciences at McGill, noting that it was easier to manage the few cases of COVID-19 in the province at that time.

That trickle turned into a rush of new arrivals after the province's early spring break, with hundreds of travellers returning to Quebec after travelling abroad. 

The study, which has not been peer reviewed, suggests what many already suspected: the early break, which began Feb. 29, was a key factor in the spread of the virus before the lockdown in mid-March.

With so many new infected people, containment became harder and this led to the tens of thousands of cases that made up the first wave of COVID-19 in Quebec. 

Researchers traced the origins of the virus by asking travellers which countries they had been to and then analyzing the virus samples in Quebec for links with different strains of viruses in other countries.

According to the study, nearly one-third of the infections in Quebec came through Europe, with 12 per cent coming from France. 

Just under 31 per cent of the virus samples studied came from the Caribbean and Latin America and around 24 per cent came from the United States, said the study. 

Few transmissions appeared to come from Asia, with around 1 per cent of cases coming to Quebec from the continent. None of those cases came from China, according to the study. 

Virus strains from Europe and the Americas were more prevalent in Quebec because more people traveled to and from those areas, making it more likely for transmissions to occur.

"With such few cases leading to community-based transmission, we all need to remain vigilant," said Dr. Sandrine Moriera, the head of genomics and bioinformatics at the INSPQ.