Mask, social distancing best bet to fight new variant

Dr. U.S. Vishal Rao

Delta was declared a Variant of Concern (VoC) by the WHO after five months since its first occurrence. However, the B.1.1.529 variant, popularly known as Omicron, was declared a VoC within a few days of the Botswana and South Africa infection reports.

Omicron has till date spread to 20 countries across the globe. Its multiple mutations hint at its fast spread and its potential to cause severe illness. It is feared that vaccine effectiveness might be lower in its case while the risk for reinfections might be higher.

The uncertainty regarding Omicron can be summarized as follows:

Transmissibility: It is not yet clear whether Omicron spreads more easily from person to person compared with other variants, including Delta. The number of people testing positive has risen in areas of South Africa, but epidemiologic studies are underway to understand if it is because of Omicron or other factors. However, with current trends in community transmission in South Africa and the imported cases in several countries, it would be safe to assume that Omicron has high transmissibility. Severity of disease: Preliminary data suggests increasing rates of hospitalization in South Africa, but this may be due to overall increase in infections, rather than specific Omicron infections. There is no information to suggest that symptoms associated with Omicron are different from those of other variants. There are initial reports in the lay press about initial cases of Omicron detected in adults below 40 years of age with atypical Covid-19 symptoms, predominantly fatigue, headaches but none of the other typical symptoms such as cough, anosmia, dysgeusia. But there is still a lot of uncertainty on the constellation of clinical symptoms of Omicron.

Risk of reinfection: Preliminary evidence suggests an increased risk of reinfections with Omicron compared to other VoCs, but more information is needed to corroborate this premise.

Vaccine effectiveness: WHO is working with technical partners to study the potential impact of this variant on our existing countermeasures, including vaccines. Vaccines continue to be a critical measure to reduce severe disease and death, including that linked to the dominant circulating variant, Delta. More data is needed to measure the vaccine effectiveness against Omicron.All Covid-19 variants, including the dominant Delta variant, can cause severe disease or death, more so in the case of most vulnerable people. Thus, prevention continues to be the principal counter measure. This is a wakeup call reminding us that the war against Covid-19 is far from over. Vaccine passport + Covid appropriate behaviour - Mask, Ventilation, social distance, hand hygiene - are still our best bets to keep the virus at bay.

Testing: S gene dropout or S gene target failure (SGTF) due to deletion at Spike position 69-70, similar to the detection of the Alpha variant, has been reported. Thermo Fisher TaqPath assay can therefore be used as a proxy test for this variant, pending sequencing confirmation. WHO guidelines state that diagnostic test kits with two confirmatory gene targets, with at least one being the ‘S’ gene, should be used for early detection of the Omicron variant. The kits should preferably contain RNaseP, Beta Actin or any human housekeeping gene as an internal control gene. As the ‘S’ gene target failure (SGTF) is indicated for Omicron, it can be used as a marker for this variant. This may lead to efficient detection of the Omicron variant of Covid. Such kits can be used as proxy tests for the Omicron variant pending sequencing confirmation. Laboratories should prioritize specimens with SGTF for genomic sequencing and confirmation of the Omicron variant. Use of the SGTF approach may lead to faster detection rates.

Analysis of the mutations in the nucleocapsid (N gene) of Omicron (B.1.1.529) viruses suggests that rapid antigen tests are currently unaffected.

In countries with sequencing capacity, WHO advises that a subset (amount will depend on local capacities – WHO is available to provide technical assistance on tailored sampling strategy) of SARS-CoV-2 confirmed cases be sequenced. Sampling selection criteria should include cases from any unusual transmission events (e.g., increased transmission despite interventions in place), unexpected disease presentation/ severity, vaccine breakthrough, severely ill patients and international travellers.

(The writer is an Associate Dean, Centre for Academics and Research, HCG Cancer Hospital.)