Cases of covid-19 infection are tending to increase to worrying levels around the world, as has been reported in recent days. Fact is, this coincides not only with the lifting of restrictions, which by far may be the main reason, but also with the announcement of the discovery of the omicron variant, of covid-19.

The UK Office for National Statistics (ONS) said on Friday that the increase in the prevalence of covid-19 infections in the past week was driven by the dominant variant delta rather than omicron.

There have been 134 confirmed cases of the omicron variant in Great Britain, which has mutations consistent with reduced vaccination effectiveness.

Prime Minister Boris Johnson has introduced travel restrictions to slow the spread of the new variant until there are more determinate studies of its characteristics.

The prevalence of covid-19 infections in England increased to about one in 60 people in the week ending November 27, from one in 65 cases reported the previous week, the ONS said, adding that 99% of all sequenced cases were Delta.

"To date, we have not identified any infections compatible with the new omicron variant (B.1.1.529) among our survey participants," he said.

However, the UK's Health Safety Agency said that by the following week there had been an increase in the proportion of tests with a distinct mutation that distinguishes omicron from delta, but which can appear in other variants.

"This is still a very small number of cases, but it is being investigated carefully to understand if it is related to travel, any other variant, or if there is evidence of omicron spreading starting in the community," he said.

World Health Organization chief scientist Soumya Swaminathan said that omicron could displace delta as the dominant variant worldwide, but that it was impossible to predict.

But for now, it is the spread of the dominant and highly transmissible variant of delta, especially among children, that is keeping infection levels high.