In search of the ‘new normal’: What will it take for COVID-19 to become endemic?
More than two years after the COVID-19 pandemic first swept the globe, we’re still learning to live with this novel disease. How close are we to the ‘new normal’, where COVID-19 is endemic, relegated into the background of daily life, and what will it take to get us there?
At the end of 2019, most people — with the exception of epidemiologists and public health experts — wouldn’t have had much call to use the word ‘pandemic’ in daily life. A few years later, and we’re probably all sick of hearing it.
Widespread vaccination in some parts of the world and the lifting of restrictions in many countries make it easy to feel that we’re moving into a new phase of living with the virus. Yet plenty of people are still catching COVID-19, being hospitalised and even dying every week, in the UK and elsewhere.
So, are we still in the throes of a pandemic, or are we moving to a stage where COVID-19 has become endemic and accepted as part of daily life? And what can we do to get there faster?
What does it mean to go from pandemic to endemic?
The dictionary defines a pandemic as an outbreak of a disease that occurs over a wide geographic area, such as multiple countries or continents, and typically affecting a significant proportion of the population.
By contrast, an endemic disease is one that is consistently present in certain populations or regions, usually with a relatively constant rate of infection (such as malaria or measles as we know them now) or predictable seasonal waves like ‘flu. This doesn’t necessarily mean mild or harmless — endemic diseases still kill many hundreds of thousands of people every year worldwide — but something we’ve learned to live with and mitigate against.
“You could say that an endemic disease is just part of the human condition, part of our lives,” says Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh. “It’s one that persists at a fairly constant level, unless something drastically changes like a vaccination programme or a problematic new variant.”
As Woolhouse explains, this constant infection rate is achieved by reaching a high level immunity across the population, often referred to as herd or community immunity, either through natural infection or vaccination (or both).
“The endemic state is a balance between the natural transmissibility of the pathogen and our immunity, and that’s what keeps it in check,” he says. “Even if we did nothing to control SARS-CoV-2 or any other new virus, it would still shift from a pandemic to endemic status in the end, because almost everyone would eventually catch it and have some level of immunity, assuming they survive.”
What is normal, anyway?
Perhaps the biggest challenge with figuring out whether COVID-19 has settled into an endemic phase is knowing what a ‘normal’ rate of infection looks like once we get there.
“The difficulty we have with SARS-CoV-2, the virus that causes COVID-19, is that because it is a new virus our baseline was zero, so we don’t know what the norm is,” explains Mike Tildesley, professor of infectious disease modelling at the University of Warwick. “It’s very hard to determine when we’ll see a shift to endemicity as there are multiple different things at play.”
Even if rates do stabilise again, there is always the risk of novel variants emerging that could set off a new wave of infections. Alternatively, the virus may evolve into a less harmful form and take up a place in our regular repertoire of grotty colds, although this is by no means guaranteed.
Looking back over previous examples, such as the 1918 Spanish flu pandemic, the HIV epidemic of the 1980s or the more recent Zika outbreak, provides few clues as to what lies ahead for COVID-19.
“Certainly in our living history we don’t have anything like SARS-CoV-2, so it is a little difficult to work out exactly how things will play out in the long run,” Tildesley argues. “The Spanish flu did mutate into a milder form that became part of a seasonal cycle, but this was over a hundred years ago and human life was very different then.”
For a start, the novel SARS-CoV-2 coronavirus is a different beast from the flu, HIV and Zika viruses, and we aren’t yet able to predict how it is likely to evolve. What’s more, a century ago we weren’t living in the globalised, interconnected societies that typify modern life and enable the virus to spread so far and so fast.
We also didn’t have an effective flu vaccine until 1942, more than 20 years after that pandemic had killed tens of millions of people around the world. By contrast, the incredibly rapid development and rollout of vaccines against SARS-CoV-2 could speed the transition to making COVID-19 an endemic disease.
“We haven’t ever had the opportunity to control a pandemic with mass vaccination before — we’re in new territory here and it’s complicated,” says Woolhouse. “We do know that vaccine immunity doesn’t last forever and wanes over time, not just for elderly and vulnerable individuals but for everyone, so we’ll need to think about what we need in terms of booster vaccination campaigns, perhaps annually.”
Immunity for the community
As Woolhouse sees it, the most likely route to reaching the high levels of protective immunity required to turn COVID-19 into a low-level endemic disease is to get to a place where most people catch the virus early in life when the risk of serious illness is very low, with vaccines and boosters providing additional protection along the way.
“It’s probably true that with SARS-CoV-2, a combination of having the vaccine and natural infection gives a higher level of immunity, which is another piece of evidence that protection builds up over multiple exposures,” he says.
One significant issue with ongoing natural infections is the risk of Long COVID — a poorly-understood constellation of lingering after effects that lasts for 12 weeks or more. Long COVID is still severely impacting the quality of life for many thousands of people who caught the disease early on in the pandemic, and its longer term effects are yet to unfold.
We do know that vaccination reduces the chances of developing Long COVID, although there is debate about the extent of this protection. We also don’t yet have enough data about the impact of more recent variants such as Omicron on Long COVID risk or how this is influenced by vaccines.
Adding to the uncertainty, most of the information we have about Long COVID so far comes from adults. There is much we still need to uncover about the long term impacts on infection on children, who would be the main population to become infected in a future endemic scenario.
While there is broad agreement that the risk of Long COVID and the risks from COVID-19 in general are lower in children than adults, there is controversy around the extent of the condition in children, and insufficient data on the impact of vaccines. As of April 2022, the NHS began rolling out vaccination to children aged 5–11, so it remains to be seen how this affects infections, immunity and Long COVID in younger age groups.
Are we nearly there yet?
There have been many uncertainties over the course of the pandemic. However, there is one thing we know for sure: COVID-19 is here to stay.
“We will always get new mutations and variants emerging and, being a respiratory virus SARS-CoV-2 transmits very easily, so zero COVID really isn’t an option,” says Tildesley. “Even with very good vaccines it would require intensive worldwide interventions that just aren’t practical, such as very strict restrictions, and as soon as you lift them then it will come back.”
So, when will we reach a point where COVID-19 fades into the background as an endemic disease, relegated to the same league as colds and flu? Unfortunately, it’s not likely to be any time soon.
“We knew from February 2020 that this was with us for decades — it was never going to be a temporary problem,” Woolhouse says. “In the UK, we’re in the early stages of the transition between having a completely unexposed population to one where almost everyone has either had COVID-19 one or more times, been vaccinated or both, but it will be many years before we know how effective the continuing build-up of immunity will be at suppressing infection and disease at a population level.”
Even when we do get there, it’s something we’ll only be able to see in retrospect when we look back over months or years of data, tracking the pattern of infections and immunity across the population. And that makes it all the more vital that this kind of data is being gathered, assessed and acted on.
“Surveillance and evaluation are absolutely critical, and we still have a challenge with rapidly evaluating how different each new variant is and how potentially problematic it might be,” Woolhouse argues. “Importantly, we need to act quickly if we think we’ve got a problem emerging, perhaps through bringing back interventions like masks or testing — my maxim for this would be early action now means less drastic action later on.”
Finally, there are the social and psychological challenges of living in the lifelong shadow of a disease that has caused so much fear and death over the past few years. As individuals and society we will have to figure out how to strike the balance between protecting the most vulnerable while not unnecessarily restricting or inadvertently harming other groups.
“We’ve done a lot of work during the pandemic on quantifying the health and non-health harms of COVID-19, and it’s really challenging to do,” Tildesley says. “What does living with COVID actually mean? And what risks are we prepared to take to live a normal life? This very much does need to be discussed, particularly as we move away from the pandemic phase into a phase of living with COVID.”
Want to know more?
If you’re a UK taxpayer, your contributions help fund the projects in this article via UK Research and Innovation — the UK’s largest public funder of research — and the nine research councils. You can read more about what we do here.
Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh is funded by the Biotechnology and Biological Sciences Research Council. (BBSRC).
Mike Tildesley, professor of infectious disease modelling at the University of Warwick receives funding from the Medical Research Council, the Natural Environment Research Council and the BBSRC.
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