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The rise of the Delta variant has upended previous optimistic projections of herd immunity and a return to normal life, with many health experts believing mask mandates and tougher vaccine requirements will be needed in the coming months to avoid more serious coronavirus surges.

While there are promising signs that California’s fourth COVID-19 surge may be starting to flatten, the fall and winter will bring new challenges as people stay indoors more often and vaccine immunity begins to wane.

The rapid spread of Delta among the unvaccinated — and the still relatively small number of “breakthrough” cases among the vaccinated — shows that significant increases in inoculations will help stop the spread. In fact, officials are now preparing to provide booster shots to those who already got their first series of vaccinations, saying the extra dose is needed to keep people protected.

Still, “the vaccines themselves are not going to likely be sufficient. And during times of increased transmission, we’ll need other tools available to protect all of us — and particularly those who, at this time, can’t be vaccinated, like our children,” said UC San Francisco epidemiologist Dr. Kirsten Bibbins-Domingo.

Read the full story on LATimes.com.