Is the Covid pandemic finally nearing its end? | Aris Katzourakis

Two years have passed since we first realized that we are dealing with a novel epidemic. In the UK, the number of deaths caused by Covid has fallen to their lowest level since the summer of 2021. What will the end of the Pandemic look like?

We won't know we have passed the end of the epidemic until some time has elapsed. The expectation is that eventually the disease will reach endemic levels, meaning immunity in the population will balance out the reproduction of the virus, resulting in a stable level of infection year on year. We won't know if stability has been achieved if the same pattern of seasonality is observed for more than one year.

There are two big unknowns in trying to figure out when the end of the Pandemic will arrive and what it will look like. How durable will our immunity be, particularly against severe disease, but also against infections? The second question is: how fast will the Sars-CoV-2 virus evolve, in particular with respect to overcoming our immune defences? The lessons the Pandemic has taught us so far are what we need to answer these questions.

The year of the Sars-CoV-2 virus was 2020, when it caused high levels of mortality and disease, and changed lives around the world. We saw a virus transmit into humans and began to observe some evolution, but thanks to the relatively slow rate of evolution, we did not observe much change beyond the immediate public health impact until the very end of the year.

The year of the variant appears to have been 2021. The Alpha variant was more transmissible and more likely to cause death and severe disease than the initial strain, which led to the reimposition of restrictions in the UK and elsewhere. The Alpha variant was more transmissible in humans than the original virus, a leap of adaptation that has never before been observed in real time. There was a glimpse into the possibility that the viruses might be able to evade the defences we had built against previous forms of the virus, by displaying a degree of immune escape. The Alpha variant was succeeded by the Delta variant, which was 50% more transmissible than the Alpha variant and brought another wave of disease and devastation.

The Omicron variant brought its own unique challenges and lessons to the table. Omicron can break our immune defences because it is evasive of the antibodies that vaccine confers. Protection against hospitalisation is not eroded to the same extent as protection against severe disease. Omicron is capable of reinfecting people who have previously been exposed to other forms of the virus. Omicron has dispelled the idea that you can get over a viral infection by being bitten. If the year of the vaccine and variant was 2021, it would be the year of reinfection.

We don't yet know how bad the re infections will be, but there will be some decline on average. Will the gap in severity between primary and secondary infections be eroded as immunity fades and the virus keeps evolving? We don't know how much secondary infections bring reduced risks of morbidity. We don't know how important reinfections are in risk groups. We cannot take the earlier success of vaccines for granted as the virus continues to evolve and the need to redouble vaccination campaigns as well as research and development is as pressing as it ever has been.

We may know how the end of the epidemic might occur in theory, and how to look for patterns to determine if we are approaching endemicity. We don't know what our future will look like when Covid is no longer at epidemic levels. Each year we are experiencing waves with a large burden of disease and death. Will endemicity continue to involve multiple waves of infections? How frequently will Omicron, which is capable of partial breaching our immune defences, arise, and will this eventually include variant that can escape the protection that vaccines induce, at least in part, against hospitalisation and death?

The behavior of this virus in countries with high vaccine rates may offer a glimpse of what the end result may look like: low risk of severe disease from any given infection, a better understanding of the cumulative disease toll of reinfections, an idea.

• Aris is a professor at the University of Oxford.