"The importance of vaccination is not only for the Delta surge but to be ready for the next surge," said San Francisco Health Director, Dr. Grant Colfax.
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Colfax says despite promising signs the city's fourth surge is starting to plateau, we still have challenges ahead.
"I think COVID is here for the foreseeable future," Colfax said.
"Is there any sign we will see a fifth COVID surge?" ABC7's Stephanie Sierra asked.
"We know it certainly could, right. I think this is the reality in this time of the pandemic," said Colfax.
In San Francisco daily COVID cases have dropped from 289 last month to 192 this week and hospitalizations have remained stable, according to county health department data. Plus, nearly 80% of the city's eligible population is vaccinated.
RELATED: Delta surge is 'clearly plateauing' in the Bay Area, UCSF doctors say
But, Dr. Colfax warned we can't let our guard down with this virus.
"There are likely to be ebbs and flows, whether it's through Delta or another variant," he said. "If we look at the UK, we see cases have leveled off and even started to increase again."
San Francisco Health Officer Dr. Susan Philip is concerned we will still see a rise in hospitalizations as they often lag behind.
"I hope this is it, but we don't know yet," Philip said. "During our third surge, if you look at that curve, we came down and went back up again."
VIDEO: 'The pathogen decides': Doctor says pandemic will end eventually, but it's not up to us
So could that mean another lockdown in San Francisco?
"No. We're keeping everything open. We are not in the mindset of shutting things down," she said. "We need to continue with the masking, encourage vaccinations and we'll have these additional vaccination requirements on the 20th."
Starting Friday, Aug. 20, vaccinations will be required for customers to enter any bars, restaurants, gyms, and entertainment venues in San Francisco where food and drinks are served. The requirements taking effect a day after the county started offering a third COVID booster shot of Pfizer of Moderna to immunocompromised patients. The rest of the country will be eligible starting Sept. 20.
Once you get a booster. How long will it last?
"It's really anybody's guess," said UCSF Dept. of Medicine Chair, Dr. Bob Wachter. "The best guess might be it will get us up to a level of immunity that was at or better than where we were after the second shot. So it should last every bit as long, if not longer."
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