Getting a flu shot is always a good idea. But infectious diseases experts say it’s crucial this year as the northern hemisphere faces a “twindemic” — the perfect storm of the convergence of COVID-19 and the seasonal flu.

It’s a scenario that could endanger an already strained health care system.

“Having two circulating respiratory viruses is not a good thing. This is something we can do something about,” said Dr. Kumanan Wilson, a senior scientist in the clinical epidemiology program with The Ottawa Hospital Research Institute and a professor of medicine at the University of Ottawa.

If COVID-19 testing centres are already exhausted and people show up with respiratory symptoms, it will overwhelm testing capacity, he said.

“From a societal perspective, we have to reduce the pressure on our health-care system.”

The flu season also presents a potential drain on families and workplaces. People with any respiratory symptoms, whether they are flu or COVID-19, will have to remove themselves from school and work.

The flu presents its own dangers. According to the Public Health Agency of Canada, there are an average of about 12,200 hospitalizations and 3,500 deaths related to the flu every year. Based on laboratory testing, there were 42,541 cases of seasonal influenza in 2019-2020.

“Everyone should get the flu vaccine this year,” Wilson said. “It’s a no-brainer.”

Concern about a potential twindemic is not overblown, epidemiologist Dr. Jeff Kwong said.

“Most health care workers would say we’re barely managing in a normal flu season. We’re always on the verge of collapse. If you add COVID, we’re in big trouble,”  said Kwong, a professor at the Dalla Lana School of Public Health at the University of Toronto.

“The biggest problem with how we view influenza is that there are other respiratory viruses circulating,” he said. “The flu is a whole bunch of viruses with a whole bunch of different presentations. They’re impossible to distinguish without lab tests.”

If people let down their guard on measures to prevent the transmission of COVID-19, such as wearing masks, physical distancing and hand hygiene, there will be a twindemic, Kwong said.

“If people keep having parties, we’ll have influenza. But, if you can control COVID, you can control influenza.”

It is also possible, but rare, to be infected with flu and COVID-19 at the same time. A study published in June in the Journal of Medical Virology found that, among 1,103 patients who had been diagnosed with COVID‐19 in three hospitals in Istanbul, Turkey, six were diagnosed as also being infected with influenza. Co-infected patients have been reported in China, Germany, Iran,  Japan, Spain and the United States.

In Canada, provinces and territories have ordered nearly 13.8 million doses of flu vaccine, an increase of 2.6 million over estimated demand at this time in 2019, said Maryse Durette, a spokeswoman for the Public Health Agency of Canada. A small reserve has also been created and it will be available for provinces and territories if needed.

So far, so good. Last year at this time, there were concerns that the flu vaccine might not be available until early November for most people because of delays in recommendations and production.

This year, flu vaccine will be made available for delivery beginning in mid-September, with most deliveries completed by the end of October, Durette said. To meet the increased demand this year, a small portion of Canada’s requirement will also be supplied in November and December.

“At the present time, no supply issues are expected this year and the increased demand by provinces and territories that has occurred since orders were first placed with suppliers in February is expected to be met in full.”

But getting the flu vaccine rolled out this year may produce additional challenges.

Health Canada has flagged some concerns, including the availability of staff and access to PPE for those who will be administering flu shots.

There are also some unknowns, including the public’s fear of exposure to COVID-19 while being immunized for flu. At the same time, there is the potential of increased demand for flu shots early in the season, something that was seen in the southern hemisphere, where the flu season starts in March.

“We don’t want people congregating as they usually do in gymnasium-type programs,” Wilson said. “We need to do it differently. And well.”

Among the possibilities according to Health Canada: drive-through and parking lot clinics in locations ranging from car washes, arenas, insurance inspection centres and drive-thu tents.

Ottawa Public Health is still working out its flu shot strategy and is to present more detail Monday at a board of health meeting.

Pharmacists, who already administer between 40 and 50 per cent of flu shots in Canada, will also be enlisted to do more.

“We’re expecting increased demand. People are already making reservations,” said Shelita Dattani, director of professional affairs at the Canadian Pharmacists Association, which has already posted a fact sheet about what to expect from pharmacies this year.

Pharmacists may be delivering flu shots by appointment, through dedicated hours for walk-in clients, special hours for vulnerable patients, off-site services such as home visits and clinics at community halls or temporary structures.

“If there is one thing you can control this year, it’s the flu shot,” Dattani said. “It’s going to be a busy year.”

For those who monitor the spread of influenza, the Australian experience of the flu season, which just ended, is a sign for hope.

According to an Australian department of health report released Sept. 6, influenza and influenza-like illness activity was lower than average across all systems for this time of year.

There were 21,119 cases of laboratory-confirmed influenza and 36 laboratory-confirmed deaths related to flu in Australia. The numbers dropped and remained low as the flu season went on.

Many who monitor the situation, including Wilson and Kwong, believe COVID-prevention measures such as physical distancing helped to reduce the spread of flu in Australia.

Meanwhile, a study published last month in the Journal of Pediatrics of almost 3,000 families found that more parents planned to vaccinate their children for flu season.

The researchers asked parents who visited 17 emergency departments in Canada, Israel, Japan, Spain, Switzerland and the U.S. between mid-March and the end of June about their willingness to vaccinate their children. About 54 per cent said they did, an increase of nearly 16 per cent from last year. Among those who did not vaccinate their children last year, almost 29 per cent planned to vaccinate this year.

Dr. Ran Goldman, a researcher and professor of pediatrics at the University of British Columbia and the study’s lead researcher, is hoping that a minimum of 70 per cent of the population will get the flu vaccine.

It’s a tall order. Having 40 per cent of the population immunized for flu in an ordinary year is considered very good, Kwong said. Only among vulnerable groups such as people over 65 and those with chronic illnesses do the numbers reach 70 per cent.

As a pediatrician, Goldman says he sees parents are more open to flu shots for their children, especially after he explains to them that children may be vectors of the flu for older people, such as grandparents. If you protect children, you are protecting everyone around them, he said.

“I’m hoping for a milder flu season, but you can’t trust luck,” he said. “We need to tell parents to roll up their sleeves … and the sleeves of their children.”

The flu shot is not 100 per cent effective, as public health authorities have to make an educated guess about what strain will be in circulation. Given the low number of cases in 2020, it has been difficult to assess vaccine match and effectiveness, Australian authorities said.

For Canada, it’s still too early to say what might happen. Another strain of flu may appear in the early spring. The flu strain in circulation in November is not necessarily the same strain in circulation in March, Wilson said.

“But, if you could reduce your risk, why wouldn’t you do it? Even in a worst-case scenario, it’s still worth it.”

Meanwhile, Wilson sees the roll-out of this year’s flu vaccine as practice for rolling out a COVID-19 vaccine —  when one becomes available — under physical distancing constraints.

“It will help us figure out the logistics.”