New BA.4, BA.5 subvariants of COVID-19 found for first time in the Sacramento area
Suspected cases of yet another group of new COVID-19 omicron subvariants, associated with steep surges in other parts of the world, have recently been identified in parts of the Bay Area and in at least one Sacramento-area county.
The Healthy Davis Together testing initiative in Yolo County reported in an update this week that it has detected 16 “possible BA.4/BA.5” cases in the last two weeks with data available: Four for the week of May 8 to May 14, and 12 for the week of May 15 to May 21.
Santa Clara County health officials on Thursday said BA.4 and BA.5, which are believed to be more transmissible than the BA.2 and BA.2.12.1 omicron subvariants dominating the U.S. amid the current surge, have been detected in Santa Clara wastewater.
BA.4 and BA.5 have become the dominant variants in South Africa and in parts of Europe. The European Centre for Disease Prevention and Control in mid-May classified both as new variants of concern, citing their capacity to evade immune protection. Federal health officials in the U.S. have not yet done the same.
The European CDC said there is no current indication that either subvariant causes more severe illness than previous versions of omicron.
California and the U.S. as a whole are already experiencing a surge in COVID-19 cases and hospitalizations due to the growing prevalence of BA.2.12.1, a more contagious offshoot of the BA.2 subvariant that the Centers for Disease Control and Prevention estimated this week made up 58% of recent U.S. cases and 48% in the CDC region including California. BA.2 made up most of the remaining cases, except about 3% for the original omicron variant, BA.1.
CDC variant proportion data do not yet track BA.4 or BA.5.
Health experts worldwide are still working to understand the two newly circulating subvariants, with some early reports saying they could lead to yet another surge in cases, or extend the nation’s current BA.2.12.1 wave.
According to Healthy Davis Together, which samples most of Yolo County’s positive virus cases for the presence of variants, possible BA.4/BA.5 made up 0.9% of all positive cases for the week ending May 14.
That grew to 2.4% last week. BA.2 and BA.2.12.1 made up 91% last week, and the original omicron variant BA.1 as well as “unspecified” lineages of omicron made up the remaining 7%.
It remains too early to predict the trajectory the two subvariants might take in Yolo County or the capital region.
For comparison, the two BA.2 lineages grew from 1.1% to 2.2% of cases — and then to 38% — during a three-week stretch from late January to mid-February, according to Healthy Davis Together data. Other earlier variants and subvariants spread along a smoother curve.
“In Yolo County, we have experienced a rise in COVID-19 wastewater measurements, cases, and test positivity rates,” county spokesman John Fout said in an emailed response. “However, symptoms from the recent variants remain mild, and we have maintained low hospitalization rates.
“The only consideration for returning to a mask mandate would be a threat to our healthcare system.”
Yolo County had the highest per-capita case rate for COVID-19 in the Sacramento region as of Friday’s update from state health officials, recorded at 35 daily cases per 100,000 residents.
But Yolo also had a test positivity rate of only 3.5%, among the lowest in California, due largely to the county’s large asymptomatic testing network.
This story was originally published May 27, 2022 at 1:18 PM.
