In March 2021, when Americans first began hearing about the Delta variant of Covid-19, breakthrough infections among fully-vaccinated Angelenos accounted for just 2% of that month’s case total. By June, when Delta accounted for 50% of all variants in Los Angeles, breakthrough infections among fully-vaccinated residents had risen to 20% of all identified cases. In late July, county officials reported that the Delta variant had overwhelmed all others, accounting for more than 90% of all positive tests analyzed for variants. As a result, the ratio of breakthrough cases increased to 30%, local health officials announced today.
While L.A. County numbers for the Delta variant have not been reported for August, as of August 19 Delta had risen to 98% of all tests genomically sequenced in California. Parallel growth in breakthrough infections has not been reported yet, but it is likely significant as well, according to Los Angeles Director of Public Health Barbara Ferrer today.