The risk of reinfection with the Omicron coronavirus variant is more than five times higher and it has shown no sign of being milder than Delta, a study showed, as cases soar across Europe and threaten year-end festivities.

Canadian drug developer Medicago’s plant-based Covid-19 vaccine candidate – enhanced by GlaxoSmithKline’s booster – was 75.3 percent effective against the Delta variant of the virus in a late stage study, the two companies said on December 7.

The Omicron variant of the coronavirus has spread to about one-third of U.S. states, but the Delta version remains the majority of COVID-19 infections as cases rise nationwide, U.S. health officials said on December 5.

Six more U.S. states confirmed infections of the Omicron variant of COVID-19 on December 3, but the Delta strain likely remains a greater threat as winter sets in and Americans gather for the holidays, experts said.

Soumya Swaminathan

The World Health Organization’s chief scientist told the Reuters Next conference on December 3 the Omicron variant could become dominant because it is highly transmissible, but that a different vaccine may not be needed.

The Omicron coronavirus variant detected in southern Africa could be the most likely candidate to displace the highly contagious Delta variant, the director of South Africa’s communicable disease institute said on November 30.

The UK Health Security Agency designated a Delta coronavirus subvariant called AY.4.2 as a “Variant Under Investigation,” saying there was some evidence that it could be more transmissible than Delta.

British health authorities, as well as global experts, are closely watching a subtype of the Delta variant that appears to be rising in the UK.

A booster dose of the Covid-19 vaccine developed by Pfizer Inc. and German partner BioNTech SE restored efficacy to 95.6 percent against the virus, including the Delta variant, data released by the companies from a large study showed on Oct. 21.

The U.S. Food and Drug Administration on Oct. 20 authorized booster doses of the Covid-19 vaccines from Moderna Inc. and Johnson & Johnson, and the regulatory agency said Americans can choose a different shot from their original inoculation as a booster.