Two new studies appear to have confirmed experts' worst fears about Omicron - protection against infection is likely weaker for both the vaccinated and those who've had a previous strain of COVID-19.
The fast-spreading variant, first detected in November in southern Africa, is rapidly taking over from Delta in places where it's got a foothold.
The evidence - based on who it's infecting - suggests its multiple mutations have given it the ability to evade protection offered by immune systems primed by both vaccines and/or infection.
Scientists at Oxford University overnight said blood samples from people who'd had two AstraZeneca or Pfier-BioNTech doses don't have enough neutralising antibodies to fight off Omicron.
Their results, published online ahead of peer review, back up findings by the UK Health Security Agency. Its analysis of the UK's first 260 Omicron cases found previously infected people had a three- to eight-fold greater chance of reinfection, and vaccines appeared to offer "significantly lower" protection against symptomatic infection.
But that didn't mean the vaccines were useless, Matthew Snape, Oxford professor and co-author of the paper told Reuters.
"[The findings] only look at neutralising antibodies after the second dose, but do not tell us about cellular immunity, and this will also be tested."
There's also no evidence yet the vaccines have lost their ability to prevent infections turning severe.
In a separate study, researchers in China looked into how well a manufactured Omicron virus was able to infect samples of blood serum taken from 28 recovered COVID-19 patients.
"We found the large number of mutations of the Omicron variant did cause significant changes of neutralisation sensitivity against people who had already had COVID," said lead author Youchun Wang of the National Institutes for Food and Drug Control.
"However, the average [protection level] against Omicron is still higher than the baseline, which indicated there is still some protection effect can be observed."
Compared to other strains they tested - including Delta - Omicron had an "enhanced immune escape".
Like the Oxford researchers, Dr Wang and his team said it remained to be seen whether protection offered by vaccines and prior infection could still prevent serious illness and death.
"More population studies including the level of immune protection and symptoms among people infected with Omicron are needed to fully establish the global impact of Omicron to the control of COVID-19 pandemic," they said in their study, published in journal Emerging Microbes & Infection.
