A team of researchers affiliated with a host of institutions in South Africa has found evidence that suggests people who have been infected with the COVID-19 Omicron variant may be less susceptible to infection from the Delta variant. The team has written a paper describing their work.
As the global pandemic has progressed, variants have emerged – some more resilient than others. Thus far, the Delta variant has proven to be the hardiest and because of that has overtaken the original virus as the most widespread of the variants infecting people around the world. More recently, the Omicron variant has emerged, first in South Africa, then all around the world.
Initial reports indicate that the new variant is much more easily spread than Delta but is less harmful to those infected—also, there has been some evidence that the booster shots given for the original and Delta variants may last for as little as ten weeks against Omicron. In this new effort, the researchers in South Africa have found some evidence of Omicron infections giving people some degree of immunity from Delta infections.
The work by the team in South Africa involved testing 15 people who had been infected with the Omicron variant—some of whom had been vaccinated and some of whom had not—to see how well their immune systems would respond to a Delta infection. They found they had all developed some degree of enhanced immunity to the Delta variant.
The researchers then tested the blood samples from the same 15 people two weeks later to see how well they put up a fight against both Omicron and Delta. In so doing, they saw a 14-fold increase in ability to overcome Omicron and a 4.4-fold increase in an ability to overcome Delta.
The researchers note that 11 of the patients had been vaccinated (and two were excluded) and that there was a good chance that most or all of them had been infected with either the original version of the virus or the Delta variant – thus it is not clear what was behind the increased resistance to Delta.
Will the Omicron variant cause more severe cases than previous SARS-CoV-2 variants?
In the first epidemiological study available, a retrospective analysis of routine epidemiological surveillance data suggest that the Omicron variant may be associated with an increase in the risk of reinfection after a primary infection . This result, obtained with the data of 35,670 suspected reinfections among 2,796,982 individuals with laboratory-confirmed SARS-CoV-2 infection, suggests that the Omicron variant has an ability to evade immunity from prior infection.
The results are not applicable to vaccination as vaccination coverage in South Africa was very low during the study. The question of an increase or decrease in the severity of COVID-19 arises with each new variant. It is common to hear some say, before any published data, that the new variant will lead to less severe cases while others say that it will lead to more severe cases, especially in children. At present, there are too many confounding factors to compare patients with the Omicron variant in South Africa with patients infected by other variants.
In fact, COVID-19 severity and mortality vary enormously depending on the country, the prevalence of vaccination, the population’s characteristics including age, socio-economic level or comorbidities, medical management guidelines or the number of simultaneous cases leading to the saturation of the health system . Large-scale case-control studies, controlled for as many of these factors as possible, are essential to seriously investigate clinical severity.
The medical management of COVID-19 cases is not expected to change with this variant. Oxygen therapy associated with corticosteroids will likely remain the mainstay of therapy. Targeted anti-inflammatory drugs, such as IL-6 inhibitors (tocilizumab) or JAK inhibitors (baricitinib) may be useful in the most severe cases.
Will monoclonal antibodies and direct antiviral drugs be affected by the Omicron variant?
Monoclonal antibodies (MAbs) are the antiviral drugs with the most evidence for efficacy in COVID-19 patients. They are now available and recommended in some countries for patients at high-risk of severe COVID-19, whether as a prophylactic treatment before infection or as a treatment after proven infection. Most of the MAbs used in these therapies are targeting the RBD of the SARS-CoV-2 spike protein, which is highly mutated in Omicron variant.
The impact of each single mutation has been studied on monoclonal antibodies efficacy  and the combination of several mutations proved to render a pseudo-virus resistant to MAbs therapies in vitro . We can expect differential susceptibility of the Omicron to MAbs in vivo depending on the antibody .
Preliminary data with single mutations in the Omicron variant suggest that VIR-7831 (sotrovimab) and VIR-7832 may retain their activity. On the other hand, no data have been published regarding Casirivimab/Imdevimab , while Bamlanivimab/Etesevimab are not expected to be effective against the Omicron variant as they already proved ineffective against Delta. However, neutralisation assays with the combined mutations are needed to conclude.
Regarding oral direct anti-viral therapies, the two current drugs that could provide a limited efficacy on SARS-CoV-2 are a ribonucleoside analog that inhibits the replication of SARS-CoV-2 and a protease inhibitor. Their mechanism of action targeting two non-structural proteins (protease and RNA-dependent RNA polymerase) should not be impacted as this variant shows few mutations on these genes, but their efficacy is not yet proved even in cases with the Delta variant.
reference link : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8660660/
More information: Omicron infection enhances neutralizing immunity against the Delta variant, medRxiv 2021.12.27.21268439; DOI: 10.1101/2021.12.27.21268439