The vaccine roll out gives hope of a return to some form of normality, but current high COVID-19 infection numbers put the success of vaccination programmes at risk. Professor Martin Michaelis and Dr Mark Wass of University of Kent’s School of Biosciences explain why
The current roll-out of COVID-19 vaccines raises hopes and expectations that restrictions can soon be eased and that there will be a swift return to some degree of normality this year. However, COVID-19 infection rates remain very high in the UK and many other countries. This is not only of concern due to the many hospitalisations and deaths but also because a high number of infections promotes virus mutations that can bypass immunity provided by vaccines or previous infections.
Viruses like SARS-CoV-2, the coronavirus that causes COVID-19, have high mutation rates. Every time a person becomes infected, viruses enter their cells and reprogramme them to produce new viruses. This virus replication process is very error-prone and every replication cycle results in mistakes, which are called mutations. Many of these mutations are damaging and disappear or are neutral and do not change virus behaviour.
However, new variants emerge occasionally, which display significantly altered properties. One example of such a new variant is B.1.1.7, which was first detected in Kent in the UK and is anticipated to be more transmissible and deadlier than other SARS-CoV-2 variants that have previously circulated. Further new variants of concern have also been described in South Africa, California, and Brazil. Since mutations happen by chance, increased transmission and virus replication automatically increases the risk of the formation of new dangerous virus variants.
Despite high COVID-19 transmission and SARS-CoV-2 replication rates, only a limited number of novel variants have been identified so far. This is likely due to a lack of selective pressure, since there is no pre-existing immunity that would favour novel variants that can escape such an immune response.
This is now changing as more people have contracted COVID-19 and the number of vaccinated individuals is quickly rising. As a consequence, there is greater immunity and an increased selection pressure that favours new variants that can bypass immune defences.
First data already suggest that the immune protection provided by vaccinations or previous infections may be less effective against some of these new variants. Initial results from the Novavax vaccine trial indicate that the vaccine protected 89% of the trial participants in the UK, but only 60% of trial participants in South Africa, where the novel variant B.1.351 is circulating. These findings are in agreement with experimental studies showing that the treatment of SARS-CoV-2-infected cell cultures with antibodies, which form a major part of the immune response, or with convalescent plasma containing antibodies from COVID-19 survivors, results in the formation of virus variants that are no longer neutralised by these antibodies. Such results provide convincing evidence that SARS-CoV-2 has the ability to adapt to the selective pressure caused by an antibody-mediated immune response.
In the current situation, we cannot completely avoid such a selection pressure and the associated risk of novel virus variants forming, but we can reduce it. The risk increases as more people are infected. Higher levels of COVID-19 spread result in more mutations that pose a risk to us, because they may be able to escape immune recognition, may be easier transmissible, and may cause more severe disease and deaths. Low levels of virus transmission result in fewer mutations and are associated with a significantly reduced risk of new mutations and dangerous virus variants emerging.
To minimise the probability of novel dangerous virus variants prolonging the pandemic, we must suppress COVID-19 transmission as much as we can. This is particularly important now, when an increased proportion of the population develops immunity by vaccination and previous infections, as this immunity results in a selective pressure that promotes the formation of novel virus variants, which can escape this immunity. If this happens, the current vaccines will be ineffective.
Whilst vaccines can be quickly adapted to new variants, the early emergence of new virus variants will significantly increase the number of COVID-19 deaths, prolong restrictions such as lockdown, and may mean that vaccination campaigns need to be started from scratch.
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