With Covid-19 cases and deaths slowing in momentum over recent weeks, some countries are rolling back restrictions amid optimism that the spread of Omicron has brought the world closer to the end of the pandemic.
Denmark has lifted nearly all restrictions. The US Centres for Disease Control and Prevention has advised that fewer communities need to continue anti-coronavirus measures such as masks and social distancing. And Britain is no longer requiring people with Covid-19 to self-isolate or take daily tests.
Globally, the number of new cases and deaths continued their downward trend, falling by 16 per cent and 10 per cent, respectively in the week ending last Sunday, compared to the previous week.
But scientists caution that the end of the Omicron surge is not the end of the pandemic, but more like the plateau experienced between previous waves over the past two years.
As immunity wanes, and another variant emerges at some point, the population could again be susceptible to mass infections, they warn.
Epidemiologist Adam Kucharski, an associate professor at the London School of Hygiene and Tropical Medicine, said it was hard to predict how long it may take for the next troublesome variant to emerge, but he pointed to similar plateaus experienced between the Alpha and Delta variants.
“Many countries with declining cases are likely to be in a ‘honeymoon period’ of lower transmission, especially if much of the reduction in transmission has come from vaccines, which can wane quickly in terms of protection against Omicron infection.”
Several European countries may well have had a post-vaccination honeymoon period against Alpha in early summer 2021, with vaccinations and post-infection immunity driving down infection rates before Delta hit, he said.
According to Kucharski, the phenomenon has been seen in other diseases and relates to the R metric used by epidemiologists to measure the spread of infection in a population.
As immunity accumulates, R, the average number of secondary cases per infection, drops. An R number below 1 marks the point at which an epidemic peaks and starts to decline.
Kucharski said that if the rate dropped considerably below 1 during an epidemic, it would take some time for susceptibility to build up to sufficient levels to see a resurgence, leaving a “honeymoon period” where infection levels remained low at first.
The phenomenon can be observed in examples like measles, with the addition of unvaccinated newborns to the population gradually increasing overall susceptibility to the illness until a threshold is reached when a new outbreak can take hold.
Kucharsky said emerging variants of Covid-19 would shape future susceptibility of populations, but how long before the next troublesome variant arose was unknown.
“We may well see further waves, depending on when variants emerge. Of course, the severity of future waves will depend on the characteristics of as-yet-unknown variants, which could turn out to be more severe like Alpha, or milder like Omicron,” he said.
Kucharski said countries seemed to define the pandemic’s emergency stage by whether it was crushing their health care systems. In countries with high vaccination rates among vulnerable groups, the Omicron phase seems to have passed, but the risk was still very real elsewhere.
“It will be up to each country to decide what a post-emergency phase looks like in the long term, but I expect we’ll still see a lot of variation globally before everyone reaches that point,” he said.
As the present wave subsides, an Omicron sub-variant known as BA. 2 is on the rise, although its parent remains dominant. Omicron BA. 1 was first identified in November and classified as a variant of concern, before taking over from the more deadly Delta.
So far, BA. 2 is dominant in just a few countries, including Denmark and South Africa, although preliminary studies suggest it is even more transmissible than BA.1.
While real-world data from South Africa, Britain and Denmark – where immunity from vaccination or natural infection is high – found no reported difference in severity of illness, the potentially greater transmissibility of BA. 2 has raised concerns of a fresh spike, or that current outbreaks will be prolonged.
“The world got lucky with Omicron, but there is no guarantee the next variant will be milder,” said Madhukar Pai, professor of epidemiology and global health at McGill University in Montreal.
“We will see new variants, because viral transmission is happening in massive numbers and over 3 billion people, mostly in lower income nations, are completely not protected.”
Vaccination rates continue to lag in low-income countries, where only 13 per cent of the population has received at least one dose of a vaccine. According to the United Nations Development Programme, 68.63 per cent of the population in high and upper middle-income countries has received at least one dose.
Pai said action was needed to get the world vaccinated, regardless of the fall in Omicron cases, to prevent another wave in coming months. To only vaccinate rich countries would be like playing whack-a-mole with a constantly mutating virus.
“The only way to end the pandemic is to end it everywhere,” he said. “Vaccinating the world is our best hope to reduce viral transmission, save lives, and rebuild the global economy.”
Pai said it was “disappointing and shameful” that Britain, the European Union and Canada were continuing to block a waiver of the World Trade Organization’s multilateral agreement on intellectual property, aimed at increasing global vaccine production.
Pai said rich nations must also share rapid tests and new antiviral treatments, as well as how to make them, for manufacture by other countries.
“Better access to tests, drugs and vaccines is the best plan to end the crisis for everyone, everywhere,” he said.
World Health Organisation chief Tedros Adhanom Ghebreyesus made a similar appeal at meeting late last month of the Access to Covid-19 Tools Accelerator, a partnership of agencies providing low and middle-income countries with tests, treatments, vaccines and personal protective equipment.
Attention must be focused on addressing “the crucial question of how we turn vaccines into vaccinations, how we ensure all countries have enough tests, enough oxygen to treat patients, and enough PPE to help health workers safe”, he said.
“We are far off track of achieving our shared goal of vaccinating 70 per cent of every country’s population by the middle of this year, as well as our targets for testing and treatment.”
In a tweet linking to the text of his speech, Tedros warned: “The Covid-19 pandemic is not over.”
Jeremy Farrar, director of the global medical research foundation Wellcome Trust, also said it would be a mistake to think the pandemic had passed, simply because cases were falling and people were fatigued.
“Everybody’s fed up with restrictions, of the news cycle of the pandemic, and of the variance and the comings and goings. But any sense that the pandemic is going to be finishing soon is nonsense,” he told a WHO research and innovation forum last month.
Farrar said it was not a given that viruses became more transmissible and less severe as they evolved. While the scenario of a transition to endemic, with immunity building up through vaccination, was positive – and perhaps the most likely one for now – it was not by any means the only one, he warned.
“There are a range of scenarios from where we are today, and clearly some countries are transitioning into a different phase. But I’m afraid the politicians around the world are focusing on the most rosy of those scenarios.”
This article was first published in South China Morning Post.