COVID-19: How past pandemics ended - CTV News

With cases skyrocketing and many scrambling to book third shots, one question feels more pressing than ever at the start of 2022: When will COVID-19 end?

The trajectory of pandemics — a term which refers to an epidemic of an infectious disease that has spread over a large region, usually globally — have varied widely depending on the type of disease, the time period, the politics and the quality of health care available. And sometimes, we consider a pandemic to have "ended" long before it ceases to be a problem worldwide.

Looking back at some of our previous pandemics or epidemics can give us an insight into how COVID-19 could come to end, both in epidemiological and social terms.

1918 FLU PANDEMIC

In the spring of 1918, the first wave of a deadly influenza started to spread. Around 500 million people —one third of the global population at the time — are thought to have contracted the virus during this flu pandemic.

One of the earliest cases was documented in March of 1918 in Kansas, U.S., but although the flu initially appeared mild, it quickly turned devastating.

People collapsed in the road. Entire towns retreated indoors, leaving the streets empty. A school in Pennsylvania started displaying the dead because funeral homes were overwhelmed.

Similar to COVID-19, the disease came in waves, making people feel as though they had defeated the virus, only be struck with another round of illness. Around four waves occurred between 1918 and 1920, with the second wave in the fall of 1918 causing the majority of deaths.

With no vaccine or treatments on the way, people attempted public health measures that are familiar to us: masking, discouraging public gatherings and trying to hold business outside.

So how did it end?

We don't have a crystal clear picture of how the 1918 flu pandemic ended epidemiologically, Alexandre White, a historian and assistant professor of Sociology and the History of Medicine at the Johns Hopkins School of Medicine, told CTVNews.ca in a phone interview.

"The hypothesis is generally that the flu either could have become more mild or ultimately kind of affected enough people such that it no longer had populations to affect at such a scale that it could remain pandemic," he said.

Essentially, the virus either evolved to be milder, or simply burned through the population.

Naomi Rogers, a professor in the history of medicine at Yale University, put it simply.

"It ran out of people," she told CTVNews.ca.

And that meant there was a massive death toll before the virus dissipated. Around 50 million people died worldwide, with 50,000 dying in Canada.

White cautioned that while the 1918 flu may have ended through the virus becoming milder or herd immunity being achieved because so many people had been exposed, this is far from a "guaranteed conclusion for COVID-19.

"Especially as we see continuing variants emerge, and the […] possibility of infection evading the immunity conferred by vaccination," he added.

But there's another aspect to how this pandemic ended, one that takes place in the collective culture.

"You could say that that pandemic ended not just when the third or fourth wave ended, but also there was a really active effort by the public and by politicians to forget it," Rogers said.

She added that while there are countless memorials to those who died in the First World War, "there are no memorials to the millions of people who died during the pandemic […] and I don't think that's a coincidence.

"By 1920, [the U.S.] elected a president who called for normalcy. And the idea was that we should put all of this behind us."

It may seem like forgetting COVID-19 would be impossible. But this does highlight how in our efforts to reach the end of a pandemic, we have sometimes failed to learn from it.

"The popular perception about history is you learn from history," Christopher Rutty, a professional medical historian and an adjunct professor at the University of Toronto, told CTVNews.ca in a phone interview. "But one of the big lessons is that we don't learn lessons from history."

SMALLPOX

Smallpox holds the unique distinction of being the only infectious disease that we have completely eradicated through vaccination — a feat that was achieved nearly 200 years after a vaccine was invented.

"I think that's the one example of fundamentally eradicating a disease that causes a pandemic," White said.

Those with smallpox developed red blisters all over their body, as well as lesions around the nose and mouth, and flu-like symptoms. Rashes found on Egyptian mummies suggest the virus had existed for around 3,000 years.

Around three out of 10 people who caught it would die, and over the years, it caused numerous distinct epidemics and pandemics.

The first vaccine for smallpox was invented in the late 18th century, and became widely accepted shortly after. By the time the World Health Organization (WHO) launched an ambitious vaccination campaign in earnest in the 1960s, smallpox had already been eliminated in North America and Europe, but was still causing outbreaks in South America, Asia and Africa.

There's a feeling that the announcement of a vaccine means the end of a pandemic — but that's not what history has shown us, Rogers pointed out. He noted that it took more than a decade after the first polio vaccine was introduced for the U.S. to become polio-free.

"Diseases don't end because you have announced that you have an effective vaccine, which is something that we have learned maybe the hard way through COVID," she said.

So can we vaccinate COVID-19 out of existence?

We were able to eradicate smallpox because it was a human only virus, meaning that it could only spread between humans and didn't have an animal vector, the way that many influenza viruses do. COVID-19 is thought to have originated in an animal before it made the jump to humans, and viruses with an animal vector always have the possibility of reemerging as a novel human pathogen, White explained.

Those with smallpox also had distinct dermatological symptoms to identify them, which is not the case with most respiratory diseases.

"I mean, we've never eradicated a respiratory disease," Rogers said.

This doesn't mean that vaccines aren't an important tool in protecting populations, as COVID-19 vaccines have been proven to be effective at preventing hospitalizations and death. But with a virus as adaptable as COVID-19, it can't be our only tool.

"There are a number of diseases that we ended that didn't include so much a vaccine, but actually included structural change, like tuberculosis and typhoid for example," Rogers said.

For COVID-19, structural changes that experts have suggested in the past include things like requiring buildings to have high-quality air filtration, overhauling the long-term care system to protect at risk populations better, or implementing more targeted testing even when cases are low to find emerging hotspots.

"I hope that in some ways, the focus on the vaccine doesn't blind us to the other ways that we have of helping to make people less vulnerable," Rogers said.

HIV/AIDS

While the virus behind it is different from COVID-19 epidemiologically, the AIDS crisis highlighted inequities in society and has had a huge impact on social behaviour and culture when it swept across the U.S. and the world in the 1980s, similar to COVID-19.

HIV is a virus which attacks the immune system and is spread through direct contact with certain bodily fluids such as blood or semen from a person with HIV who has a detectable viral load.

If untreated, HIV can lead to AIDS, an advanced stage of infection that can lead to death within three years without treatment.

Around 36.3 million people have died of HIV, according to WHO.

"I actually think AIDS is a really important and powerful analogy to COVID," Rogers said. "It's very interesting to think about the kind of lessons we did didn't take from that pandemic."

White added that a "frustrating, but reoccurring, theme in the history of pandemics and epidemics" is how governments and society as a whole often ignore the threat of infectious disease if they see the populations being affected as not "satisfactorily important as to warrant major responses."

At the beginning of the AIDS crisis, the issue was viewed as a problem affecting only gay men, a group which authorities were comfortable ignoring.

"Significant resources were denied," White said. "Research was slow to develop and ultimately, thousands of people lost their lives as a result of a lack of co-ordinated public response."

The stigma surrounding AIDS also allowed the disease to spread further than it may have if there had been an early response. It took community-driven research and organizations to develop an understanding of the disease and push governments to act.

So when and how did it end?

It hasn't. There is still no cure for AIDS, and no vaccine, although some candidates are in trials. Around 1.5 million people acquired HIV in 2020, according to WHO, and 680,000 people died of HIV-related causes.

However, in North America, widespread access to reliable treatments allow a person with HIV to live a full life without fear of dying of AIDS or spreading the virus. These antiretroviral drugs work by stopping the virus from replicating inside the body.

Pfizer's new antiviral pill for treating COVID-19 is actually a protease inhibitor, a type of antiretroviral drug that was first developed to treat HIV.

However, not everywhere has easy access to these drugs.

"Now AIDS is considered an infectious disease that reflects the resources of the country," Rogers said.

White pointed out that often we consider a pandemic to have "ended" when the threat has diminished within wealthier nations or within the Western world.

HIV is a clear example, he said.

"Once access to effective antiretroviral therapies emerge and become easily accessible, we tend to lose interest or perceive that the real pandemic threat has dissipated, when in actual fact, the ravages from the disease continue to persist in earnest and very extreme in places [which] lack the access to the healthcare and support," he said.

"We've seen that perspective raise up in relationship to COVID-19, especially in the last few months, once vaccine access had largely been primarily achieved in wealthier nations, only to, over the last several weeks, recognize that without so effective vaccination around the world, we're going to see, potentially, severe variants of concern continue to pop up around the world in places that lack effective vaccination coverage."

In the fall, as Canadians were enjoying a return to many regular activities due to high vaccine intake, experts warned that a lack of global vaccine equity could lead to new variants developing in regions with less access to vaccines.

Then along came Omicron.

"If COVID is raging in different parts of the world, it's hard to really insulate yourself effectively," Rutty said. "Just what's happening with the Omicron is a classic example."

SO WHICH WAY COULD COVID-19 GO?

Could the COVID-19 pandemic burn through the human population and then evolve to become weak enough that it's no longer a pandemic-level threat? Could it become a seasonal issue held at bay by yearly vaccination? Could wealthy nations conquer COVID-19 in their regions through vaccination or new treatments and then consider the pandemic over while it flourishes for years in lower-income countries?

Rutty explained that there's never a straightforward answer when we try to apply history's pandemic lessons to a current or future virus.

"There's rarely a peace agreement with a virus, you know, like an end of a war," he said.

"It's not just a matter of epidemiology or vaccine technology or science. It's as much about politics and human behavior, and all these other kind of non-scientific things that are really having a major impact on the course of the pandemic."

One of the most likely scenarios, Rogers predicted, would be closer to the 1918 pandemic, with COVID-19 eventually becoming seasonal and milder.

"My guess would be that it's going to become much more like the flu, that it's going to be endemic, and then there'll be particular seasons of the year where it's more likely to be a potential outbreak," she said.

In terms of the cultural idea of a pandemic "ending," she added that we could also see a scenario similar to AIDS "where we might consider it over, but it's not over globally."

But unlike in 1918, when all people could do was wait for the flu to evolve until it became weaker, we understand how this new virus works and spreads. We have vaccines and other treatments either existing or in the works to combat COVID-19, and avoid such a massive death toll.

"I would be dissatisfied, deeply dissatisfied, if our acceptance of COVID-19 forces us to accept a world in which hundreds of thousands or millions of people continue to be exposed or at risk of severe illness and death," White said.

"If we don't put these efforts into practice and impose effective practices that we know will save lives, then we should take a good hard look at ourselves in the mirror and think about the sort of societies that we're leaving to our children."