Ultra-contagious BA.4, BA.5 subvariants fuel coronavirus spread in California, Australia

In a sign of how the new coronavirus wave continues to spread across California, two-thirds of the state’s counties are now in the high COVID-19 community level, in which the U.S. Centers for Disease Control and Prevention recommends universal masking in indoor public spaces.

This comes as health officials are warning of concerning weeks ahead as two new ultra-contagious Omicron subvariants — BA.4 and BA.5 — spread. Experts believe the subvariants, which are not only especially contagious but also capable of reinfecting those who have survived earlier Omicron infection, are a major factor behind the continued persistence of coronavirus transmission across California.

So far, Los Angeles County health officials have not imposed new masking rules. But they have warned that might be necessary, perhaps later in July, if new coronavirus-positive hospitalizations continue to rise. Though experts are concerned, there is still uncertainty about how serious a summer wave will get.

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