In this Nov. 8, 2021, file photo, a window sign at Portland's Elm Street bus station reminds customers to wear a mask. Credit: Troy R. Bennett / BDN

A newly identified coronavirus variant sparked alarm on Friday, with world health officials raising concerns that it could be more contagious than the delta iteration, which has been responsible for a massive surge in cases in Maine in recent weeks.

The World Health Organization designated the B.1.1.529 variant, now known as the omicron strain, a variant of concern on Friday after health officials in South Africa flagged it amid a rapid rise in cases there. It has also been detected in a handful of other countries, including Belgium and Hong Kong, and U.S. officials announced travel restrictions on eight African countries with the goal of preventing the spread of the variant here.

Much remains unknown about the new strain. The threat it poses will depend largely on whether it is more likely to infect vaccinated people or if it is otherwise more transmissible than the delta variant, which accounts for nearly all new cases here. Maine’s past experience with variants shows how new strains can die off quickly and how a more contagious version can arrive later here than the rest of the U.S. but still become dominant.

The omicron variant caught the attention of health officials due to quick growth in cases in South Africa and genetic analysis showing it has more mutations than previous strains. Researchers worry that means it could better evade immunity from vaccines or previous infections, though those concerns remain speculative for now.

The strain has not been identified in the U.S. yet, although there is a possibility that it has circulated here undetected. Nearly all COVID-19 infections both in Maine and across the U.S. over the past few months have been the highly contagious delta variant, according to state and federal data.

Variants, including delta, have generally shown up in Maine later than they did elsewhere. Estimates from the U.S. Centers for Disease Control and Prevention, for example, pegged delta as accounting for more than a quarter of all virus cases in the country in June, while genomic sequencing in Maine revealed it represented only 3.6 percent of cases here that month.

That experience also shows how quickly a more contagious strain accelerates. Delta went from that small share in June to nearly 90 percent in July and it has shown up in nearly all tested samples since then.

It has also driven the state’s overall rise in infections. Total cases are now more than 20 times higher now than they were in early July. Maine set a new record for weekly cases earlier this week, with the seven-day infection rate surpassing a previous peak from January, before vaccines were widely available. The state also set a new record with 327 COVID-19 hospitalizations on Thursday.

Not all new variants turn out to be a significant threat. One first detected in South America made headlines this fall when the World Health Organization declared it a “variant of interest” after scientists in the United Kingdom reported that it might be more resistant to treatment.

But the mu variant had actually been detected in Maine months earlier, accounting for 11 percent of cases here in June, according to state data. It was quickly overtaken here and elsewhere by the delta strain as the summer went on. It has not been detected here since July.