Two new sub-variants of Omicron are spreading throughout the US, leaving experts concerned about their transmissibility amid America’s ongoing Covid-19 pandemic.
According to new data from the Centers for Disease Control and Prevention (CDC) published on Tuesday, sub-variants BA.4 and BA.5 now account for almost 13% of all new Covid-19 cases in the US between 29 May and 4 June, making up 5.4% and 7.6% of cases, respectively.
A week ago, both strains accounted for 7.5% of new cases and only 1% of new diagnoses in early May, reports the New York Times, though previous CDC estimates have been erroneous.
Both sub-variants are classified as variants of concern by the European Centre for Disease Prevention and Control (ECDC), reports Reuters, indicating “a significant impact on transmissibility, severity and/or immunity”.
The majority of new cases are still caused by the Omicron subtype BA.2.12.1, another highly contagious Omicron sub-variant, though some experts believe that BA.4 and BA.5 could eventually outcompete it.
Scientists have warned that the new sub-variants are more contagious forms of Covid-19 that could escape immunity from past infections and vaccinations, causing breakthrough infections.
Both subtypes have also spread rapidly across the world, with the World Health Organization (WHO) in May blaming the new sub-variants for a rise in cases in over 50 countries.
In South Africa, where the subtypes originated, both sub-variants are dominant.
Amid a rise in cases driven by the BA.5 subtype, Portugal reported 26,848 new cases and recorded 47 Covid deaths on Thursday, the highest number of deaths reported since 17 February.
In the US, the two subtypes have spread particularly in the south, throughout states including Texas, New Mexico, Arkansas, Oklahoma and Louisiana. In the region, BA.4 and BA.5 made up over 22% of new cases last week, according to CDC data.
Scientists remain unsure if the latest sub-variants cause more severe infections, leading to increases in hospitalization or death.
The US is currently experiencing its fourth-highest surge of Covid-19 cases, with experts believing that the current rate of infection is much higher than actually reported.
The latest spike in cases comes as cities across the US have largely dropped mask mandates and other Covid-19 health protections.
“For the summer, going into the winter, I expect these viruses to be out there at relatively high levels,” said Dr Alex Greninger, assistant director of the University of Washington’s clinical virology laboratory, to CNN. “Just the number of cases, the sheer disruptions of the workforce – It’s just a very high, high burden of disease.”
BA.4 and BA.5 were first detected in South African in January and February of 2022, respectively.
