Rising Omicron cases indicate that we have to remain cautious.

Although COVID-19 is currently not dominating the headlines, it has not gone away and it would be prudent to remain vigilant to avoid unpleasant surprises. By Martin Michaelis and Mark Wass.

COVID-19 numbers and hospitalisations have started rising again. This is not a surprise after control measures have been lifted. COVID-19 spreads wherever people meet. Hence, if we increase the number of our contacts and reduce mitigating measures such as wearing face masks, avoiding crowded indoor venues, and isolating ourselves when we have symptoms and/ or test positive, there will be an increase in COVID-19 transmission. This is what we saw in the past when restrictions were eased, and this is what we are seeing again now.

When it comes to ‘living with COVID’, a central question is what level of COVID-19 spread we are going to accept as a society. There are still more than hundred deaths daily with COVID-19 on the death certificate. However, this does not seem to cause major concerns among the wider public. Looking at our behaviour and the public discourse, it seems to be accepted that COVID-19 causes disease and death, as long as hospitals are not so overloaded that they have to turn patients away. Basically, the general consensus appears to be that everything is fine as long as there are hospital beds and intensive care unit beds for everyone, who is seriously ill.

It is difficult to estimate how the situation will develop. Nobody knows how big this spike is going to be or how long it will last. Since the number of tests performed every day has drastically declined, it is likely that the daily case numbers miss many more cases than in the past. Notably, the random samples taken by the Office of National Statistics Coronavirus (COVID-19) Infection Survey have always shown that the actual number of COVID-19 infections is substantially higher than the number of reported cases. Therefore, COVID-19 surveillance will depend the more on the data from the Office for National Statistics Coronavirus (COVID-19) Infection Survey, the fewer COVID-19 tests are performed and reported to the NHS.

It is also not yet clear the extent to which an increase in cases and hospitalisations will translate into increased COVID-19 deaths. Four main factors influence this:

1) Vaccinations and previous infections have established a substantial level of immune protection in the UK population. So, a much smaller proportion of infected individuals will progress to severe disease and death than at the beginning of the pandemic.

2) The currently dominant Omicron variant appears to be inherently less severe than the previously dominant Delta variant.

3) Omicron is a so-called ‘immune escape’ variant that is much better at infecting vaccinated individuals and people who previously had COVID-19 than previous variants.

4) Immune protection provided by vaccines and previous infections wanes over time. So, while there is currently a high level of immunity in the UK, our vulnerability to COVID-19 has already begun to increase again.

Since we do not know how the combination of these factors will shape the current Omicron wave, we will have to wait whether, and if yes to which extent, the number of COVID-19 deaths will follow the rise in COVID-19 cases. Notably, it takes two to four weeks from diagnosis to COVID-19 death in the majority of cases and it is not clear how quickly waning immunity will make an impact. Therefore, it may take months before we can draw conclusions on the death toll of the current peak.

Notably, these considerations only apply to the current Omicron wave. Once a new variant emerges, everything may be completely different. For example, a new subvariant of Omicron, called BA.2, has emerged and it may behave differently from the original Omicron BA.1 variant. Scientifically, it seems most likely that we will continue to see further COVID-19 waves caused by novel variants for the foreseeable future. These variants may be milder or more aggressive than previous variants. The more we reduce our surveillance, for example by reducing testing and cutting down the Office for National Statistics Coronavirus (COVID-19) Infection Survey, the less likely are we to detect novel variants early. This means that we may only learn of new variants when hospitals fill up again.

Booster vaccines have been shown to restore waning immunity at least in part. Hence, they are in the absence of other measures the only strategy to keep COVID-19 under some level of control. However, it is not entirely clear how effective future boosters will be. Data are available suggesting that a fourth vaccination improves protection, but the additional impact may not be as pronounced as that provided by the third one. Moving forward, COVID-19 vaccines will probably need to be adapted to novel variants, instead of continued boosting with the original vaccines.