The Omicron variant of SARS-CoV-2, which represents a step-change in the Covid-19 pandemic with record numbers of new daily infections being reported around the globe, has undergone fundamental changes that may explain its spread and disease. Researchers at the MRC-University of Glasgow Centre for Virus Research have used laboratory experiments and real world infection data to investigate Omicron. The results, published as a pre-print study and not yet peer-reviewed, from laboratory tests showed that Omicron is largely unaffected by the antibodies provided by two doses of Covid-19 vaccine, but responses are improved by a third-dose booster.
This has been confirmed by analysis of real-world infection data; Omicron escapes immunity from two vaccine doses, but three doses restore good levels of protection. The escape from vaccine-induced immune responses means that over time, Omicron-specific vaccines would be required if disease severity was high, either directed at the general population or vulnerable groups.
Further, the study also provided evidence that Omicron has switched its route of entry into human cells, from cell surface fusion to cathepsin-dependent fusion within the endosome.
This fundamental biological shift is likely to influence Omicron spread and the types of cells it can hijack. These changes may also affect the pathogenesis and severity of disease, and researchers say they require further evaluation in population-based studies.
First detected from South Africa and Botswana in late November last year, the virus has spread rapidly to more than 100 countries. It has also outpaced the previous Delta strain in many countries to become the dominant variant. The countries include the US, the UK, Italy and Portugal among others.
