Never one to use two words when six will do, the British Prime Minister Boris Johnson has reached for a range of verbal contortions to predict an end to the COVID-19 pandemic.
He’s used the 1815 battle of Waterloo—“the morale-boosting bugle-blasting excitement of Wellington’s Prussian allies coming through the woods”—to describe vaccinations, and warned against the premature lifting of restrictions by invoking Steve McQueen’s fate in the 1960s movie The Great Escape: “if we try to jump the fence now, we will simply tangle ourselves in the last barbed wire.”
Despite the verbose promises of victory as vaccine programs around the world accelerate, the pandemic is unlikely to end with the knock-out blow against the virus that Johnson and other political leaders promise. The best we can hope for, scientists predict, is an uneasy truce.
I don’t think that anyone who is reasonably well-informed about infectious diseases and how they move in populations thinks we are going to eradicate COVID.—Kate Baker, University of Liverpool
“The chances of this disease going away are very small,” says Kate Baker, an infectious disease researcher at the University of Liverpool in the UK. “I think we’re going to end up tolerating a certain level of disease.”
In simple terms, the future of COVID-19 comes down to one of two possible paths. Either we eradicate the virus, or we don’t. And if we don’t, then the disease will become endemic, Baker says. Future generations will share their world with SARS-CoV-2 with the same weary familiarity as we do already with germs that cause everything from influenza to measles to the common cold.
“I don’t think that anyone who is reasonably well-informed about infectious diseases and how they move in populations thinks we are going to eradicate COVID,” Baker says.
The world has managed to stamp out viral diseases before, including the original SARS outbreak that killed hundreds when it swept through southeast Asia in 2002–’03. That virus spread from people who already showed symptoms, which made it relatively easy to prevent onward transmission by quarantining those who were sick. In contrast, people infected with SARS-CoV-2 are unknowingly contagious for several days before they become ill, if they ever do.
Given such asymptomatic transmission, the only way to eradicate COVID-19 would be through a sustained global vaccination program, says Graham Medley, an infectious disease modeller at the London School of Hygiene and Tropical Medicine who is helping to advise the UK government. This was done with smallpox in the 1970s and has almost been achieved with polio today, with the disease remaining endemic in just Afghanistan and Pakistan.
For these viruses, vaccines are available to provide so-called sterilizing immunity. The immune response generated by the vaccines is so effective it stops people becoming ill and stops them from passing on the disease to others. Although COVID-19 vaccines reduce the severity of symptoms, there is little evidence they block transmission, and experts tell The Scientist they think it is unlikely.
“My bet is against that. Not anything against the vaccines, but it doesn’t seem like that’s how our immunity to coronaviruses typically works,” says Jennie Lavine, a biologist at Emory University in Atlanta.
Even if there were a COVID-19 vaccine that introduced sterilizing immunity, and enough people could be persuaded to take it, eradication is far from guaranteed. Such an effort would take years and would be hugely expensive, particularly as populations would need booster jabs periodically to protect them from possible flare-ups.
“We would have to keep vaccinating if it existed anywhere else in the world,” says Medley. “Eradication requires a large global coordination, which is just not there at the moment. We have a vaccine that works but we don’t have the political, social, and economic structure to distribute it equally around the world.”
For these reasons, experts expect that COVID-19 will become endemic, a term epidemiologists reserve for when disease spread settles at a relatively stable baseline level—in other words, the phase after a rapidly growing epidemic.
The endemic future of COVID-19
An epidemic slows to make a disease endemic as the number of available susceptible hosts drops over time, so that each infected individual passes the disease to just one other person on average. Without vaccines, this steady state emerges only when large numbers of people are infected and then either die or gain immunity. By safely offering immune protection, vaccinations against COVID-19 will speed this transition to endemicity, and massively reduce the death toll along the way.
Exactly how the disease will show itself once it becomes endemic is unclear, Lavine says. A modelling study she published earlier this month in Science suggests it will pose a similar threat to existing common-cold viruses. Catching the SARS-CoV-2 virus once or twice in childhood, the study concluded, should then prevent people from getting severe disease from it later in life. “We don’t know the answer to that yet because we haven’t had enough time. But from data on other coronaviruses that seems extremely likely,” she says.
Key to this prediction is that COVID-19 continues to trigger mild or no symptoms in children when they are exposed to the virus for the first time. Such childhood exposure can then be tolerated by society because it grants lasting immune protection, topped up by regular re-exposure to the circulating virus.
The world has probably been here before. The four coronaviruses identified as responsible for many common colds are thought to have been far more dangerous when they first emerged as human diseases. “Some of these we think were the basis for what people at the time called flu epidemics or pandemics,” says Marc Veldhoen, an immunologist at Lisbon University in Portugal.
Studies suggest that the so-called Russian flu that killed 1 million people in 1890 may have been caused by the human coronavirus OC43, Veldhoen says. “And now it’s endemic.” The end of the SARS-CoV-2 pandemic, he says, may only be the start of our relationship with this virus.