San Francisco and its suburbs have been cautious, maintaining various restrictions while other parts of the country reopened businesses and eased mask mandates. Meanwhile, its vaccination rate is among the highest of any major U.S. city, with two-thirds of all adults have received at least one dose.
And as parts of the city open up, experts are offering cautious optimism. The city may be seeing signs of herd immunity. Herd immunity is about transmission. If enough people can’t catch and spread a virus, particularly in a community that already has few cases, the virus struggles to find new hosts. Eventually, infections would naturally taper off. It’s a simple concept, yet it can be elusive and difficult to define, particularly at the national level.
Still, herd immunity is not a fixed target, and the threshold can vary depending on several factors, including population dynamics. Achieving herd immunity also doesn’t automatically guarantee the coronavirus will simply fade away. There’s also a risk that a variant of the virus could emerge that escapes the protection of vaccines. There is no evidence to suggest that has happened so far, but if it did, it could jeopardize the protection that communities have built up.
While San Francisco may be the first major U.S. city that appears to have wrested control of the pandemic, others are likely not far behind.
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