Starting later this week, if you received the one-shot Johnson & Johnson vaccine, you're eligible to drop into the vaccination clinic at SF General and get a "supplemental" mRNA vaccine dose — but don't call it a booster.

The decision was made Monday by Zuckerberg San Francisco General Hospital (ZSFG) and San Francisco's Department of Public Health (SFDPH), as ABC 7 reports, following multiple reports that the J&J vaccine may not be as effective in preventing infection from the Delta variant as mRNA-based Pfizer and Moderna vaccines. With the first variants of COVID-19 that were spreading last year, the J&J vaccine was seen as highly effective in preventing severe illness, but new data suggests that the mRNA vaccines provide strong protection against what appears to be a stronger and more infectious variant.

But they are being careful to call it a "supplemental dose," not a booster.

"It's not a booster because it's not specific for some of the variants, which the booster ultimately will be," says Dr. Chris Colwell, chief of emergency medicine at ZSFG, speaking to ABC 7. He adds, regarding the decision to offer these mRNA extra shots, "Potential benefit, no downside. To me, as we look at the future of this virus and now we're facing a fourth surge, it does make sense."

"[SFDPH] is currently accommodating special requests from individuals who have received the Janssen (Johnson & Johnson; J&J) viral vector COVID-19 vaccine and in many cases have consulted with their doctor and wish to receive a supplemental dose with an mRNA vaccine (Pfizer or Moderna)," the SFPDH says in a statement. "This move does not represent a change in policy for SFDPH. We continue to align with the Centers for Disease Control and Prevention guidance and do not recommend a booster shot at this time. We will continue to review any new data and adjust our guidance, if necessary."

San Francisco appears to be unique so far in offering such supplemental shots, though anecdotally is seems that many people around the country who received the one-shot J&J vaccine have sought out their own supplemental vaccines out of concerns over the Delta variant.

Dr. Lisa Winston, ZSFG's Chief of Staff and Hospital Epidemiologist, tells ABC 7 that the decision to offer the shots is not based on any CDC guidance or FDA emergency use authorization, but they feel comfortable offering them nonetheless.

In June, Reuters reported that some infectious disease experts who had themselves gotten the J&J vaccine had sought out their own supplemental "boosters," despite there not being published data to support the benefit of these.

"There's no doubt that the people who receive the J&J vaccine are less protected against disease," said Stanford professor Dr. Michael Lin, in the Reuters piece. "From the principle of taking easy steps to prevent really bad outcomes, this is really a no brainer."

The ZSFG vaccine clinic is open for drop-ins from 8 a.m. to 4 p.m. on weekdays at 1001 Potrero Avenue, Building 5, 2nd Floor. The supplemental shots should be made available by Thursday or Friday. Call 628-652-2700 for more information.

The hospital is prioritizing SF city residents for the shots, but Dr. Winston tells ABC 7 that they will accommodate residents of other counties as long as supplies hold up.

Top image: A pharmacist volunteer prepares doses of the Johnson and Johnson COVID-19 vaccine during a pop-up clinic at Western International High School on April 12, 2021 in Detroit, Michigan. The state of Michigan has seen an explosion of COVID-19 cases despite a massive effort to roll out vaccines. Pop-up clinics in various communities are one of the ways the state government is trying to get the surge under control. (Photo by Matthew Hatcher/Getty Images)