New Covid-19 cases in London have stopped accelerating. The number of people testing positive everyday is still a large number, but the exponential rate at which it was growing over the past fortnight appears to have now become a little linear.
The trend, and whether it reflects the actual outbreak dynamics, could hold some lessons for regions preparing to face an Omicron wave. Outside of South Africa, the variant of concern has spread the furthest in the UK capital, possibly accounting for as much as 80% of new cases (if a particular testing artefact is considered) and has triggered a record surge in infections.
That the growth rate has plateaued was proposed by Cambridge-based mathematician Alex Selby, who runs a Covid-19 tracker drawing from the several official data streams.
“There are still a LOT of new cases per day but if there really is zero growth in new cases then that is highly encouraging. What could have caused it?” he wrote in a Twitter thread on Monday.
“It can’t be herd immunity -- the effect is far too quick for that. The only genuine way to change growth in infections that quickly is changes in behaviour, i.e., people not meeting other people as much. The alternative would be that it’s all an artefact due to the testing system struggling to keep up, or fewer people choosing to get tested,” he added.
{{/usCountry}}“It can’t be herd immunity -- the effect is far too quick for that. The only genuine way to change growth in infections that quickly is changes in behaviour, i.e., people not meeting other people as much. The alternative would be that it’s all an artefact due to the testing system struggling to keep up, or fewer people choosing to get tested,” he added.
{{/usCountry}}The actual reasons are hard to ascertain. But looking at the two main possibilities offers some implications that other regions should pay attention to.
Possibility 1: Testing has hit a ceiling
The record surge triggered by Omicron in the South African Gauteng province, where Omicron first spread widely, and the UK, created concerns that demand for tests will outstrip availability.
Gauteng has seen a similar plateauing of new cases. Its growth rate has been in negative on some days, but that has been attributed by South Africa to holiday season travel, when tens of thousands of people leave the province that contains the country’s biggest city Johannesburg for their homes.
Testing in London, and the UK in general, is unlike in most other regions in the world: the state-run National health Service (NHS) offers citizens free rapid test kits – known locally as lateral flow device, or LFD – to take Covid-19 tests at home. These tests are in addition to the PCR tests at laboratories, and LFD positive cases need to be confirmed by PCR tests.
Of late, there have been anecdotal reports of LFD shortages and the waiting time for PCR results seem to have grown by a couple of days. “Positivity (positive results per test) is around 20% which is high, but it doesn’t sound overwhelming, and though there are certainly some delays in getting rapid tests, there doesn’t seem to be a major testing capacity issue yet,” Selby contended.
Elsewhere in Europe, there are more clear signs Omicron can push testing capacity past its breaking point. Recent positivity rates in Denmark have been above 47% and the government is now looking at hospitalisations as the key metric, said Mads Albertsen, co-founder of DNASense, a testing lab in Denmark.
Hospitalisations cannot be an early beacon for an incipient Omicron outbreak, which means countries, particularly densely populated ones like India, will need to strengthen testing capacity for a demand surge. Rapid tests, especially those that people can buy cheaply to take at home, could be key.
It is crucial to remember Omicron is more transmissible than Delta, and the older variant had triggered a testing crisis in India at the peak of the March-April wave.
Possibility 2: Behaviour change among people
A second possibility could be that people are able to get tested but are choosing not to because they do not want to have to isolate during Christmas, Selby said. “It’s not easy to discount this completely, but I think it’s unlikely because overall numbers being tested are holding up well,” he said.
But behaviour change could also genuinely be helping cut new transmission, or at least reduce it from the exponential rates that were prevailing. Google Mobility Report data showed significant drop in visits to workplaces, markets, recreation spots and other businesses, giving at least some indication that people have become more careful.
In fact, a study by Yale University researchers, published in the Proceedings of the National Academy of Sciences in April, found that people become more careful when cases begin spiking, and it is the surge of new wave that spurs on voluntary behaviour changes. The study found that government-mandated restrictions too led to behavioural change, but the substantial part, at least in the American context, was voluntary.
This serves to redouble focus on Covid-safe behaviour. In India, some states are expected to enter an election cycle, with an announcement of poll dates expected early next month.