SAN FRANCISCO (KGO) -- As the July Fourth approaches, if you are fully vaccinated should you wear a face mask at a large outdoors event?
Dr. George Rutherford: "Depends on how packed it is. If it's really packed I might do it. The recommendations are if you're in a crowed event with more than 10,000 people outdoors is recommended that you wear a facemask. It's not required. It's recommended."
Since June 15, COVID cases have increased in the Bay Area and according to Dr. Rutherford, the fireworks show in San Francisco with potentially thousands in attendance could put many who are unvaccinated at risk.
"In terms of mixing vaccinated and unvaccinated the risk isn't for the people who are vaccinated. The risk is for the people who are unvaccinated coming in contact with someone else who's unvaccinated and infectious," explained Dr. George Rutherford, UCSF Professor of Epidemiology.
Dr. Rutherford is attributing this risk to the Delta variant. First detected in India and now accounting for 36% of COVID cases in California.
"In the old days with the original set of variants if you had a case in your household you had about a 20% chance of getting infected, now it's probably close to 50% so it's that much more transmissible. So in these large crowd settings where people who are unvaccinated are congregating especially indoors it can spread pretty quickly," said Dr. Rutherford.
Keeping that in mind San Francisco will have COVID safety guidelines in place for the Fourth of July celebration.
"The guidance is that if you are unvaccinated you should be wearing your mask when you are in crowds. Even if you are outdoors," said Adrienne Bechelli, Deputy Director for Emergency Services SFDEM.
In past years Pier 39 has been packed with people lining up to watch the fourth of July fireworks and this year city officials are expecting thousands to gather on Sunday.
"We are the only county in the Bay Area who is hosting a big fireworks celebration and it's due to our vaccine success in the city," said Bechelli.
In most cases Dr. Rutherford says it is safe to remove your mask.
Dr. George Rutherford: "Yes, it is. Unless you happen to be a person who had therapeutic or naturally immune suppressed for a reason or a solid organ transplant. You have a greater chance of vaccine failure. It still mostly works, but you have a greater chance of vaccine failure than people who are not immunologically disadvantaged."
74% of San Franciscans are fully vaccinated but with an event of this size city officials are also accounting for residents from across the Bay to attend who may be unvaccinated.
"We are really comfortable having this event because of the regional success of all our vaccinations. San Francisco has done really well and so have all our surrounding counties so we do feel comfortable and confident having other people come to visit," said Bechelli.
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