A succession of more-transmissible SARS-CoV-2 variants has emerged over the past year, each harbouring a constellation of mutations. The most worrisome so far is the so-called delta variant.
Is delta more virulent?
Possibly as it appears patients are more likely to be hospitalised with delta than with the previously dominant alpha strain. A large UK study published in Lancet Infectious Diseases showed Covid-19 patients have a 2.3 times increased risk of being hospitalised within two weeks if they have delta compared with an alpha infection. That fit with an earlier study from Scotland that showed the risk of hospital admission was almost doubled in those with delta versus alpha. Doctors in India have linked delta to a broader array of Covid symptoms, including hearing impairment. Other evidence found delta had some propensity to evade antibody-based treatments and carries an increased risk of reinfection in those who have recovered from Covid caused by another strain.
How do variants affect the vaccines?
Scientists pay the most attention to mutations in the gene that encodes the virus’s spike protein, which plays a key role in its entry into cells and is targeted by vaccines. The four variants of concern — alpha, beta, gamma and delta — all carry multiple mutations affecting the spike protein. That raises questions about whether people who have developed antibodies to the “regular” or “wild type” strain — either from a vaccine or from having recovered from Covid — will be able to fight off the new variants. In most instances, the variants of concern do lead to a reduction in vaccine effectiveness of varying degrees, though the shots mostly retain their ability to protect against severe disease, according to the WHO.
What else is out there?
The WHO has highlighted the risk that more variants will emerge given the ongoing high rates of transmission globally. For example, scientists in South Africa reported in August a potential variant of interest dubbed C.1.2 that carries “concerning constellations of mutations”. It was first identified in May in the provinces of Mpumalanga and Gauteng, where Johannesburg and the capital, Pretoria, are situated. By August 13, it had been found in six of South Africa’s nine provinces as well as the Democratic Republic of Congo, Mauritius, Portugal, New Zealand and Switzerland. Even in South Africa, as of late August, C.1.2 comprised just 2 per cent of the known SARS-CoV-2 variants spreading there.