As countries compete ferociously for resources to fend off the COVID-19 pandemic, the government of Canada may want to start planning ahead for the next viral wave set to sweep over the planet: the annual influenza season.

Virologists and infectious disease specialists say the selection of this year's flu vaccine — always something of a hit-and-miss undertaking — will be critical to reducing the impact of a second wave of COVID-19 that the U.S. Centers for Disease Control (CDC) has warned could be worse than the first because it will coincide with the the annual arrival of the flu.

"There's a possibility that the assault of the virus on our nation next winter will actually be even more difficult than the one we just went through," CDC director Robert Redfield warned this week.

The success of this year's flu vaccination campaign will be critical to Canada's ability to control the novel coronavirus for three reasons: hospital capacity, co-infection (having both diseases at once, which could compound their effects) and the limited supply of COVID test kits.

The need to plan ahead

CBC News asked Health Canada what it's doing this year to ensure it isn't caught short if there is a global scramble similar to the one we are seeing now as countries compete for scarce medical supplies during the next wave of flu.

CBC also asked if the government of Canada intends to mount a more aggressive vaccination campaign than usual.

"The Public Health Agency of Canada is planning ahead for the potential for simultaneous outbreaks of the flu and COVID-19 infections in Canada this fall," spokesperson Geoffroy Legault-Thivierge told CBC News.

"To help minimize challenges this may cause to the health care system, the 2020 flu campaign will put a special emphasis on at-risk populations such as seniors and people with compromised immune systems or with underlying medical conditions."

Ottawa Public Health administers a free flu-shot clinic at City Hall on Nov. 20, 2019. Seniors are more vulnerable to health complications from the flu. (Stu Mills/CBC)

Typically, the stated goal of the annual vaccination drive is to reach an 80 per cent vaccination rate in vulnerable populations, such as those over 65. In the past three years, that rate has fluctuated between about 65 per cent and 71 per cent.

But the vaccination rate for 18 to 64-year-olds is much lower. Usually, only about a quarter of people in that population group bother to get a flu shot. Even among those with chronic medical conditions, fewer than half get vaccinated.

'Double whammy'

Flu season is usually the time of year when Canadian hospitals are at their busiest. To some extent, Canadian hospitals are designed to deal with that seasonal surge.

But if a second wave of COVID-19 lands on top of a bad flu season, it could break the system, said virologist Jason Kindrachuk of the University of Manitoba.

"You have the issue of overwhelming health care workers," he said. "There is a high burden of severe influenza illness in the risk groups that we see hit really hard with COVID-19. That includes people aged over 65, those with chronic respiratory conditions, but that also brings into play children."

Not much is known about how the two diseases might interact, but we know that it's possible to have both COVID-19 and seasonal flu at the same time. Both illnesses attack the respiratory system and both cause fever. Some infectious disease specialists, such as Dr. Greg Poland of Minnesota's Mayo Clinic, have warned that having both diseases at once likely would produce a "double whammy" effect.

Kindrachuk said there's a less obvious side effect of flu season that could undermine efforts to get the COVID-19 pandemic under control — the fact that people who get flu may assume they have COVID-19 and waste large numbers of badly-needed COVID test kits as a result.

Nurses with the William Osler Health System perform COVID-19 testing near Etobicoke General Hospital in Toronto on April 14, 2020. Health system experts say that, because COVID-19 and the common flu share some symptoms, the coming flu season could ramp up demand for scarce COVID-19 tests. (Evan Mitsui/CBC)

"We have two diseases that look fairly similar, at least in the early stages," he said. "If you have people that present with influenza-like symptoms, one of the things we're hoping to be able to do is to potentially rule out the possibility of influenza."

But Kindrachuk said doctors' ability to rule out flu will depend on the patient being immunized for flu in the first place. It also will depend on the flu vaccine being the right one for the strain of influenza that happens to be going around at the time — something that is never guaranteed.

'Flu is a beast'

Although SARS-CoV-2, the virus that causes COVID-19, appears to be more deadly than most strains of influenza, coronaviruses mercifully lack the flu's ability to continually mutate.

Influenza "is a beast," said Kindrachuk, "and we know that it changes frequently from year to year.

"We have multiple circulating strains, so trying to get a universal influenza vaccine that gives us close to 100 per cent efficacy in coverage — that is the dream of every virologist that does any sort of infectious disease research. But we're not there yet."

The design of each year's flu vaccine is the outcome of a worldwide effort. First, the World Health Organization collects data from over 100 countries' national influenza centres. Then, five virology centres — in Atlanta, London, Tokyo, Beijing and Melbourne, Australia — analyze the data and propose a vaccine composed of three or four strains of influenza A and influenza B.

Last year's vaccine was a mix of strains first detected in Kansas, Colorado, Brisbane in Australia and Phuket in Thailand.

It pays to start early

Although Canadians normally don't see the flu vaccine until mid to late fall, preparation begins much earlier, said Kindrachuk.

"We start getting an idea from Australia during the summertime, because being in the southern hemisphere, this is their winter season," he said. "That's when we tend to see some indication of what the flu season may be like.

"The problem is that's all predictive, so the particular flu strain that may hit Australia quite hard may not be the one that we get hit with. And we saw that last year, when here in North America we had an over-representation of influenza B."

The private companies that manufacture flu vaccines need a lot of time to grow the vaccine — a process that usually involves injecting it into chicken eggs and letting it reproduce, then extracting and processing it.

"It takes at least six months to produce large quantities of influenza vaccine," says a CDC document on the issue. "For vaccine to be delivered in time for vaccination to begin in the fall, manufacturers may begin to grow one or more of the vaccine viruses in January based on their best guess as to what viruses are most likely to be included in the vaccine."

Sometimes, their best guess is very good. Sometimes it isn't. Getting it right is going to be especially important this year.

The danger of shortages

Last winter in Canada, there were shortages of Flumist, a nasal spray flu vaccine for those who react poorly to injections.

Geoffroy Legault-Thivierge of Health Canada said there is still time to order more flu shots.

"In light of the COVID-19 pandemic, provincial and territorial governments are reviewing their vaccine supply orders for next year's influenza season to determine whether they are sufficient or should be increased," he said. "There is still an opportunity to increase orders before final commitments need to be made."

But the clock is ticking and demand is likely to be stronger than usual all around the world.

As Australia heads into its flu season, its government is already warning citizens to get vaccinated. But Australia only has enough vaccine doses for about half its population.

South Africa is also reporting that it doesn't have enough doses for this year, despite having ordered a year in advance.

"I think we have to be proactive and start the messaging early," said Kindrachuk. "COVID-19 is not going to disappear by the fall ... but we can do everything we can to reduce that stress on both testing and health care networks."