Covid Update: New Variant – Booster Even More Important

Arcturus (formally XBB1.16) is a new SARS-CoV-2 variant closely related to the dominant COVID virus Omicron strain. The sequence changes in the virus spike protein appear to convey a transmission advantage, although early reports suggest that it does not cause more severe disease than previous Omicron variants.


Data from India comparing XBB1.16 incidence in February and March 2023 of this year showed an increase from 15.3% to 58.6%. More recent data from Los Angeles show that XBB1.16 accounted for 10% of COVID cases as of the end of April, up from 3% only 2 weeks earlier. Given these trends, Arcturus could be the dominant strain locally in the next couple of months.


“Some countries are experiencing surges of infections three or four times each year, driven largely by the breakneck pace at which the virus continues to change, says Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Center in Seattle, Washington. Currently, SARS-CoV-2’s spike protein, in which most immunity-evading mutations occur, is evolving at twice the rate of a similar protein in seasonal influenza and about ten times as quickly as those of cold-causing ‘seasonal’ coronaviruses (Nature, May 4, 2023). The article predicts relatively frequent “wavelets” of infections year-round, unlike the seasonal flu outbreaks.


Because of the close relationship to earlier Omicron variants, the current bivalent vaccine-boosters containing Omicron sequences should provide protection against serious disease. Because there has been a significant uptick in hospitalizations in India linked to Arcturus infection, it is really important that those over 65 or with compromised immune systems get another Pfizer or Moderna booster sooner rather than later. As of May 2, only 43% of individuals in the US 65 years or older had got one booster shot, and no data are yet available for how many seniors have gotten a second booster. I really hope that Del Mar residents are doing much better than the national average.


Don’t be misled by the “ending” of the COVID pandemic emergency status. The virus is here to stay, and we need to adapt to its presence. The latest data for California (April 20 to 26) has 421 daily hospitalizations and 115 weekly deaths due to COVID. These results may worsen as Arcturus becomes the dominant variant. Get that second booster shot before this happens.