It is two years since the World Health Organization (WHO) declared Covid-19 a global pandemic. Society has reopened, life has resumed. Attention has turned, understandably, to the harrowing crisis in Ukraine. No one would blame you for hoping you’d heard the last of Covid. Yet on Thursday, the director general of the WHO tweeted that the pandemic is “far from over”.
Given the removal of mitigations by the Westminster government you would be forgiven for thinking differently. Speaking to friends and relatives, they seem surprised that Covid cases and hospitalisations are rising again, and have been for the past two weeks. In south-west England, hospital admissions are already higher than at the peak of the Omicron wave. The south-east will soon follow. In order to understand the implications of these recent upticks for the future of the pandemic, we need to put our finger on what caused them. Is this just a bump in the road towards high-level endemicity, or do these figures herald the start of yet another NHS-threatening wave?
There are a number of competing hypotheses that might explain why we are seeing rises. It could be waning immunity, changes in testing, the relaxation of mitigations, behavioural change, a new variant or any combination of these. Looking more closely at the data, we can start to eliminate some possibilities. These rises are probably not the result of waning immunity from boosters. The booster rollout was staggered by age, so if immunity was waning, we’d expect to see cases and hospitalisations increase in the older age groups, who are now further from their booster. We aren’t, though. Cases in different age groups all started to increase at roughly the same time. On top of this, the latest edition of the Office for National Statistics’ antibody survey shows high percentages of adults (95% or above) in the UK continue to have Covid antibodies.
So if not waning immunity, could it be the BA2 subvariant of Omicron, which has recently become dominant across the UK? It’s possible that the rise of this more transmissible strain could be contributing to the increases in cases and hospital admissions that we’re seeing. There’s also Deltacron, the nickname for a variant first detected in France in January, with similar-looking variants found in the Netherlands and Denmark. It won’t yet be contributing significantly to the numbers in the UK, but may play a role in coming months: its presence in multiple locations suggests it’s not a flash in the pan.
But the most obvious explanation for the rise in rates is the impact of Downing Street’s removal of all remaining Covid mitigations, including self-isolation. This will undoubtedly have led to more infections and hospitalisations, and may well have been enough to reverse the trend of falling cases we had been enjoying for almost two months previously. Hospitalisations and cases began to increase around the same time in all regions and in all age groups, supporting the idea that this national-level edict, and the behavioural change it has engendered, are the root cause of the recent losses of the precious ground we gained in the battle against Covid.
What is perhaps harder to explain is why hospitalisations started rising at the same time, or even slightly before, cases did. There is usually a lag of seven to 10 days between people testing positive and hospitalisation, if required. Usually we’d expect to see cases rise ahead of hospital admissions.
We know there have been recent alterations to testing requirements and test accessibility, so perhaps we are seeing the impact of those changes in the data. Hospital settings, in which testing availability and behaviour shouldn’t significantly affect numbers, might have picked up the increases earlier, while drops in community testing gave the artificial appearance that cases were falling. The latest data from NHS England suggests that most Covid patients in hospital do not have Covid as their primary diagnosis, which might indicate some degree of in-hospital infection. That said, even when Covid is not the primary diagnosis, it may still be the trigger for the underlying cause of hospitalisation and so may also need to be treated.
Whatever the cause of the recent increases, even if cases plateaued around current levels, this would still constitute bad news. Endemicity has been one of the most misappropriated and misunderstood concepts during the pandemic. It means roughly constant levels of infection, but says nothing about how high those levels are and how severe their impact: the common cold is endemic, but so too is malaria. Smallpox was endemic, until eradicated. Endemic does not mean benign. While we fail to take measures to mitigate the pandemic, we will continue to suffer a high disease burden. Despite what politicians say, the pandemic is not over. And while Covid may have been forgotten by some, it is far from gone.
Kit Yates is director of the Centre for Mathematical Biology at the University of Bath and author of The Maths of Life and Death
