Two relatively new variants of the omicron strain of coronavirus, BA.4 and BA.5, have been gaining ground in the United States in recent weeks. This momentum comes as the country appears to be returning to pre-pandemic norms, even as the pandemic continues to see a revival in some communities and sectors.
According to data from the Centers for Disease Control and Prevention (CDC), BA.4 and BA.5 – which were linked to a surge of infections in South Africa during April and May – already account for roughly 13% of detected cases in the United States. Their share has grown rapidly, signaling a shift in the circulating variants and a potential impact on transmission dynamics nationwide.
Just a week earlier, these variants represented about 6% of cases, and a month prior their presence in the United States was minimal. The rapid rise suggests that BA.4 and BA.5 are spreading at a notably high rate, outpacing other circulating strains. This trend has prompted continued monitoring by public health officials and researchers who are assessing how these variants interact with immunity from vaccination and prior infection.
White House covid-19 response coordinator Ashish Jha, in an interview with NBC, indicated that projections show BA.4 and BA.5 likely becoming the most common coronavirus variants in the United States by late summer or early fall. These projections reflect modelling that considers transmission rates, seasonal factors, and the level of population immunity, among other variables.
First detected in South Africa in early 2022, these variants are more contagious and have a greater ability than other omicron strains to bypass immune defenses. Despite their enhanced transmissibility, current evidence has not demonstrated that BA.4 and BA.5 cause more severe disease compared with other omicron lineages. The observation remains that vaccination, boosting, and prior infection continue to influence the severity profile of infections.
The United States is navigating a moment of mixed signals about the pandemic, with broad economic and social activities resuming while preventive measures like masking are no longer ubiquitous in many settings. At the same time, reported infections are rising in certain communities, and many experts warn that the official case counts may underestimate the true scale of transmission due to testing patterns and reporting delays. Public health authorities stress the importance of staying up to date with vaccinations, including boosters as recommended, and practicing protective measures in higher-risk environments when appropriate. (CDC)