COVID-19: WHO says Omicron has 'growth advantage' over Delta, overall risk 'very high'

In a new document outlining the virulence and transmissibility of the Omicron B.1.1.529 ‘highly divergent’ COVID-19 Variant of Concern, the World Health Organization (WHO) has warned that the Omicron strain appears to have a growth advantage and will spread at a much faster rate than the hypervirulent Delta strain.

“Omicron is spreading faster than the Delta variant in South Africa where Delta circulation was low, but also appears to spread more quickly than the Delta variant in other countries where the incidence of Delta is high, such as in the United Kingdom,” WHO cautioned in a report documented by the Technical Advisory Group on Virus Evolution. 

Although, the global health body said that whether the Omicron’s observed rapid growth rate in countries with high levels of population immunity is related to immune evasion, intrinsic increased transmissibility, or a combination of both, remains uncertain at this time. But the WHO warned countries that Omicron will “outpace the Delta variant” where community transmission occurs, adding there are limited data to ascertain the intensity of the ‘severity’ of the COVID-19 disease caused by Omicron. 

“The overall risk related to the new variant of concern Omicron 'remains very high’ for a number of reasons,” WHO warned.

“First, the global risk of COVID-19 remains very high overall, and second, preliminary evidence suggests potential immune escape against Omicron induced infection and high transmission rates, which could lead to further surges with severe consequences,” it explained. 

Altered antigenic profile of Omicron spike reduces vaccine protection: WHO 

Citing the preliminary findings from South Africa, WHO said that as seen in the Omicron cases there, the symptoms may be less severe but it is too early to say as the variant is in the initial phases of the spread.

“All cases reported in the EU/EEA to date have been mild or asymptomatic, it remains unclear to what extent Omicron may be inherently less virulent,” informed WHO.

The health body also stressed that the vaccine efficacy on B.1.1.529 to date is not fully known as there is limited available data and no peer-reviewed evidence.

WHO emphasised that the considerably altered antigenic profile of the Omicron spike protein suggests a “reduction in vaccine efficacy against infection and transmission associated with Omicron.” The incidence of reinfection has increased in South Africa, warned WHO. Those who had developed the antibodies from previous COVID-19 infection had a lower neutralisation activity on Omicron in case of reinfection, the global health body stressed.

The monoclonal antibodies that proved effective in the case of Delta variant “will need to be tested individually, for their antigen binding and virus neutralization,” WHO informed adding that enhanced surveillance with rapid testing and stricter contact tracing of cases suspected cases with Omicron Variant Of Concern “is strongly advised to interrupt chains of transmission.”