At this present juncture, San Francisco's positivity rate for COVID-19 sits at 5.1% — sparking concern amongst experts at John Hopkins University. Why? The last time SF saw such a high positivity rate was in January at the start of that season's holiday surge, which later peaked at 18.9%.

Over 84% of San Franciscans have completed a full COVID-19 vaccine series; more than 90% of the city's denizens have received at least one shot of a vaccine to protect against the coronavirus. The seven-by-seven still has one of the most vaccinated cohorts of any large metropolis, anywhere in the world. But as more communicable variants and subvariants — like BA.2 Omicron — continue emerging, test positivity rates, which is the average number of positive results yielded from a batch of COVID-19 tests, will inevitably climb.

That said: Health experts at John Hopkins University warn that any observed test positive rate of 5% or more is cause for concern.

"The higher the percent positive is, the more concerning it is," reads a paper published by the public health school around understanding COVID-19 testing information. "As a rule of thumb, however, one threshold for the percent positive being 'too high’ is 5%."

Back in May, the WHO (World Health Organization) recommended the "percent positive" remain below 5% for at least two weeks before governments consider reopening. San Francisco has now surpassed that — two days after SFMTA lifted its mask-wearing requirement on public transport vehicles.

City data referenced by NBC Bay Area showed that the last time San Francisco saw an over 5% positivity rate was in January; that single-digit percentage point would eventually climb to 18.9% amid the height of this past winter's COVID-19 Surge. By March, things had calmed and positivity rates went back down to 2.4% — before inching back up earlier this month.

Nevertheless, the increase in new case numbers isn't enough to sound the alarm in the city, according to San Francisco Department of Public Health officials, noting that they're not worried about this spike... (yet).

“While case rates have been a key measure of the virus’s spread, we also look to indicators of severe disease such as hospitalizations and deaths to inform public health decisions and to make decisions on how to best deploy resources to meet the needs of highly impacted communities,” the City health department said in a statement to the Chronicle.

Right now, San Francisco's 5.1% COVID-19 test positivity rate is a whole two percentage points higher than the state average. And considering the city's test positivity rate has already climbed by 0.5% since earlier this week, it's likely we'll consider seeing a rise in the coming week(s).

Related: Nearly One In Six Attendees Got COVID at San Mateo High School's Prom

Photo: Medical personnel take a sample from a person at a drive-thru Coronavirus COVID-19 testing station at a Kaiser Permanente facility on March 12, 2020 in San Francisco, California. Kaiser Permanente has opened a drive-thru Coronavirus test station where patients who are exhibiting signs and symptoms of the Coronavirus can be referred by a physician to be tested. (Photo by Justin Sullivan/Getty Images)