When we’re infected with SARS-CoV-2 (the virus that causes COVID-19), or when we are vaccinated, the immune system is primed to protect against future infections.
The relative levels and duration of immunity against SARS-CoV-2, either attained through infection (“natural”), vaccination (“artificial”), or both (“hybrid”), are not completely clear. But 66% of the world’s population is estimated to have some form of immunity against SARS-CoV-2. This immunity is more likely to provide protection against severe illness and death, but offers some protection against infection.
In countries such as the UK and the US, more than 95% of people currently have immunity (measured via antibodies), up from 5% in December 2020. There’s no doubt that the virus now has a lower chance of inflicting serious damage compared with two years ago.
At the same time, the experience of the winter 2021-2022 wave shows that vaccination alone is unlikely to eliminate the virus. In contrast to smallpox, rinderpest, and even measles, we might need to learn to live with it.
A steady influx of children born without exposure to COVID and waning immunity among adults is likely to fuel future waves.
A changing virus
In 2020 there was speculation that in contrast to other coronaviruses, SARS-CoV-2 would not mutate fast enough to cause problems after vaccination. This has proved wrong, and the rise of variants such as alpha, delta and, most recently, the subvariants of omicron, have shown their potential to escape immunity from vaccination and prior infection.
Since mid-2022, the virus has been spreading not as a single dominant variant but more as a mixture of descendants. When transmission is high in winter, a new dangerous variant might emerge and cause a large wave like a year ago. But at the moment there’s no clear sign that this might be happening.
To spread, SARS-CoV-2 must pass from an infected person to a susceptible one, travelling in tiny particles through the air. Like other respiratory diseases, COVID spreads more when people mix indoors, like in schools, offices, or at Christmas parties. Lockdowns, self-isolation and masks have been remarkably successful in slowing down the epidemic.
But the economic and social effects of lockdowns have been controversial. As the vaccines currently protect the majority of people from severe illness and death, there is little will for reintroducing the restrictions. But, the return to pre-pandemic contact levels is likely to keep COVID circulating for longer.
Ventilation, masks, and strengthening our immune systems are currently the best ways to counterbalance the effect of the increase in social contacts on COVID transmission.