Dec 22 (Reuters) - California will require healthcare workers and workers in "high-risk congregate settings" to get a COVID-19 vaccine booster by Feb. 1, Governor Gavin Newsom said on Wednesday as part of the state"s response to the highly transmissible Omicron variant. The mandate follows a Sept. 30 order for the state"s healthcare workers to be fully vaccinated. "We recognize now that just being fully vaccinated is not enough with this new variant, and we believe it’s important to extend this requirement to getting that third dose, to getting boosted," Newsom said at a briefing. State employees who still have not received a booster must undergo testing for COVID-19 twice each week before the Feb. 1, deadline, Newsom said in a statement. Workers have been allowed to request exemptions for religious or medical reasons. While California, the country"s most populous state, exceeds the national average for full vaccinations with 65.5%, it slightly lags the national average in booster shots at just under 30%, according to the Center for Disease Control and Prevention. Although California has one of the lowest COVID-19 infection rates in the country, Newsom cited recent developments showing that new cases nearly doubled in the past week as the Omicron variant of the coronavirus sweeps the country. "I"m mindful at this moment, with (one of) the nation"s lowest positivity rates -- the sixth lowest case rates -- that that can change in a matter of days, not just weeks or months," he said. The governor also announced that all public school students, from kindergarten to 12th grade, will receive a rapid COVID-19 test as they head back to school from winter break, adding that the state was ordering 6 million test kits. The state has accounted for only 0.3% of school closures, even though it has 12% of the country"s student population, he said. California also will expand the hours of state-operated testing centers that have reached capacity, Newsom said.