No, hundreds of Canadians have not died from COVID-19 vaccines. Where does this myth come from?

In a cycle that has now become familiar, the tweet drew a storm of criticism and then was deleted.

Alberta politician Brian Jean had claimed that data from Health Canada says that up to and including June 24, there was a total of 355 reports of death following vaccination."

In a followup tweet this month, Jean - a contender in the race to replace Jason Kenney as the province's next premier - said he'd meant to include a link to more information.

But the comments made Jean another high-profile figure to apparently buy into a persistent myth among vaccine critics - the idea that COVID-19 vaccines have led to hundreds of deaths in Canada and other countries.

That's not what the numbers say.

Billions of COVID-19 vaccine doses have now been administered around the world, saving millions of lives, and have been closely monitored by many countries for adverse health effects that experts say are extremely rare.

But many who have been critical of vaccines, including such high-profile figures as Robert F. Kennedy Jr. and Tucker Carlson, have used online reports of vaccine side-effects to argue the shots are less safe than they really are.

Canada is among the countries that publish reports on side-effects, which experts warn can be cherry-picked by anti-vax campaigners to make false claims.

I find it frustrating, honestly, when politicians start to try to interpret scientific evidence, because they really don't have the expertise or the background to be able to do it," said Julie Bettinger, a professor of pediatrics and vaccine safety scientist at the Vaccine Evaluation Centre in Vancouver.

I think it also then politicizes a situation where it's not warranted and can likely lead to more deaths."

Like many bits of misinformation, this one started with a real-life statistic that experts say is being misinterpreted.

Health Canada lists on its website all reports of adverse reactions following vaccination. According to the site, the number of deaths has actually increased since Jean's tweet. As of July 22, there had been 366 reports of someone dying after COVID-19 vaccination.

But here's the important part: a death after vaccination isn't the same thing as a death resulting from vaccination.

In other words, while 366 people have died following their vaccination, most of those deaths were determined to be unrelated to the shot, or there has not been enough information to establish a link.

A coroner in Ontario included a blood clot related to vaccination in one person's cause of death. About 50 deaths remain under investigation at the federal level.

For comparison, 88 million vaccine doses have been administered in Canada, and more than 43,000 people have died of COVID-19. Since the start of the vaccination campaign, about half of COVID deaths have been among the unvaccinated, despite this group being a small minority of the population.

While death is the most serious outcome, Health Canada also tracks other side-effects. The data shows that so far, 0.057 per cent of doses have prompted an adverse event such as headache or fever, while 0.012 per cent of doses led to a serious adverse effect, such as a blood clot or heart attack.

Before being rolled out to the public, coronavirus vaccines were tested on thousands of volunteers, whose every post-vaccination medical complaint was scrutinized. Some side-effects, including fever and muscle soreness, were found to be related to the vaccine. Some people were hospitalized, and researchers adjusted the vaccine's eventual dosages as a result.

But researchers cast a wide net: during Pfizer's pediatric vaccine trial, one child swallowed a penny after being vaccinated, which was duly recorded as an adverse event. (It was ultimately found to be unrelated to vaccination.)

As your high school science teacher may have put it, correlation does not equal causation.

The misconception that the vaccines are linked to a high risk of death has flourished, unsurprisingly, on social media.

National Public Radio in the U.S. did an analysis last year and found that articles linking vaccines with deaths were among the content that drew the most engagement online. They also calculated that an American is about three times more likely to be struck by lightning than to die after a COVID vaccine.

Tucker Carlson, the cable news personality, is among the people to spout the same misinformation south of the border, stating on his show last spring that thousands of people had died following vaccination. He was citing a U.S. database of side-effects known as the Vaccine Adverse Event Reporting System, or VAERS.

The U.S. numbers in particular have been quoted by vaccine critics so often that the Office for Science and Society at McGill University in Montreal, which is devoted to science education, wrote an article imploring people to not fall for the VAERS Scare' tactic." Although the database plays a vital role" in detecting side-effects of vaccines, it was being weaponized to terrify the public," author Jonathan Jarry wrote.

Canada has two systems designed to keep track of adverse reactions to vaccines. The Canada Vilgilance Database collects reports from manufacturers, health-care professionals and people who have been vaccinated.

Meanwhile, the Canadian Adverse Event Following Immunization Surveillance System, or CAEFISS, collects numbers from all the provinces, territories and federal departments. All of those reports are pooled and posted on a publicly available website.

There's no time limit on reporting adverse events, Health Canada says, but 95 per cent are reported within the first 42 days.

Vaccine experts want serious events to be reported so they can learn as much as possible, said Dr. Karina Top, an associate professor of pediatrics and community health and epidemiology at Dalhousie University in Halifax, who specializes in vaccine safety.

We want people to report so those reports can be analyzed," she said. That's casting a wide net to make sure that we don't miss anything that could be important."

But experts say those numbers are just a jumping-off point.

Health Canada has said that of the 366 deaths reported so far, about 112 are unlikely" to be the result of a COVID-19 vaccine, and another 204 didn't have enough information. Another 50 cases remain under investigation.

When it receives a report, Health Canada said its experts verify the diagnosis, look at past medical history and medications, and review all information submitted. They will sometimes go back to the reporting jurisdiction to ask for more information.

But sometimes, certain details needed to determine a cause of death can't be obtained, explained Dr. Christine Navarro, a public health physician at Public Health Ontario. In some cases investigators can't obtain them through either interviews or medical records, and in some cases tests were not performed at the time.

That investigation is critical in answering the question of whether a death is the result of vaccination, or just a coincidence. The scientists assigned to the task, who may include experts in blood clots, vaccines and public health, use a general set of principles, said Bettinger of the Vaccine Evaluation Centre in B.C.

First they look at whether the timeline makes sense. Did the side-effect happen only after vaccination? Did it happen again if the patient received a second dose? Scientists will also look at whether the same side-effect is being reported in other parts of the country, or elsewhere in the world.

Then, and this is a really important one, but is it biologically plausible? Could this actually have been caused by the vaccine?" Bettinger said, giving the example of a car accident: It's not really biologically plausible that a vaccine is going to cause someone to rear-end somebody else."

Health Canada says a causality assessment is usually completed within a week or two, but it may take longer if more information must be collected.

Of the 50 cases of death under investigation in Canada, the most high-profile are the six deaths related to blood clots in people who received the AstraZeneca vaccine.

According to Health Canada, 64 people were reported to have blood clots with low platelet levels. Of those diagnosed, the average age was 57, slightly more were men, and most were diagnosed after their first dose. The AstraZeneca vaccine is no longer being used in Canada.

The provinces also do their own vaccine monitoring. In Ontario, there was one case in which a coroner said that a person's cause of death included vaccine-induced immune thrombotic thrombocytopenia, or VITT, Navarro said in an email.

The vaccine safety system has successfully detected new safety signals and rare and very rare adverse events following COVID-19 immunization," she added.

Bettinger runs yet another vaccine safety monitoring program known as the Canadian National Vaccine Safety (CANVAS) Network. Normally it's hard at work monitoring the rollout of flu vaccines, but when COVID hit, it was asked to pivot.

If you think of the two federal surveillance systems as a sort of 911 line for vaccines - in that all sorts of people are encouraged to report serious effects, which then prompt an investigation - Bettinger's program does some of the ongoing detective work on how the vaccines are performing more generally.

Under CANVAS, researchers have recruited more than 1.8 million volunteers who have been vaccinated and follow them, surveying their health at periodic intervals. They also compare those people to a control group who haven't been vaccinated, to get a better sense of what may have been caused by the vaccine and what wasn't.

This allows researchers to get more detailed information on how the vaccines affect people. Their latest findings, published in the journal Lancet Infectious Diseases, found that vaccines were not only safe in pregnancy, but that pregnant people actually had lower rates of post-vaccination health events than the general population.

Top, the Dalhousie professor, notes that the last significant safety issue picked up around the world was the rare, usually mild cases of myocarditis - inflammation of the heart muscle - caused by mRNA vaccines in some patients. The early American data on vaccine rollout among children also looks good, she adds.

We know more about this vaccine than most of the other vaccines that we've been using for a lot longer just because of the sheer number of doses, the intensity of the surveillance, and the huge amount of research that has been done in many different countries," she said.

These are safe vaccines that we now have a lot of experience with."

Alex Boyd is a Calgary-based reporter for the Star. Follow her on Twitter: @alex_n_boyd