Pandemic shows signs of slowing in San Diego

Amid fresh signs that the pandemic is slowing, the county health department confirmed that 43 infections related to the Mu coronavirus variant have been detected in the region, going all the way back to April.

San Diego County posted its most positive coronavirus report in weeks Wednesday, reporting four straight days with new case totals under 1,000 and Monday’s total at 519, the lowest single-day number reported since July.

COVID-related hospitalizations also are showing a downward trend, reaching 609 across all local hospitals Tuesday after peaking at 695 on Sept. 1.

California’s latest estimates of the county’s effective transmission rate now puts it under 1, coming in at 0.89 for San Diego County. Numbers under 1 indicate that each new case is generating, on average, fewer than one additional case, meaning that the pandemic is on a shrinking trajectory.

Brett McClain, executive vice president and chief operating officer at Sharp HealthCare, said Wednesday that those numbers have recently translated to lower numbers of tests coming back positive over the last week as the number admitted with COVID-19 has receded a bit.

“It has looked a little promising in the past week,” McClain said. “ I feel a little more encouragement than I have in a while.”

Dr. Seema Shah, medical director of the county’s epidemiology and immunization department, said the current pattern in the numbers does signal a change in the local status of the pandemic.

“Yes, we’ve currently hit a plateau, but the three-day weekend may very well have changed that,” Shah said.

Whether Labor Day weekend produces another surge of cases, followed by inevitable increases in hospital admissions and deaths, comes down to just how much immunity existed in the community when the parties happened.

It is easy to see how many are protected by vaccines. More than 2.1 million people countywide are fully vaccinated, according to the county’s latest report, representing about 63 percent of the population and including about 500,000 kids younger than 12 who are not yet approved for vaccination.

As of Wednesday’s weekly update, 2.4 million county residents had received at least one vaccine dose, out of the 2.8 million residents age 12 and older who are eligible. That means that about 290,000 county residents were partially protected as the weekend rolled around, with about 380,000 eligible but still unvaccinated.

Of course, surviving a coronavirus infection leaves protective antibodies in the blood that continue to help fight off the virus for an unknown number of months after recovery.

Because many have mild or no symptoms after becoming infected, it is impossible to know precisely how large the group of people with natural antibodies is, though county records show that about 56,000 residents tested positive from July 1 through Sept. 7. An official count of how many of those were not vaccinated was not available Wednesday evening, but the latest county report estimates that about 80 percent of new cases confirmed since Aug. 9 have been in unvaccinated residents.

With hundreds of thousands of kids and adults still unvaccinated and likely lacking natural immunity, now is not the time to celebrate good news in the weekly numbers, Shah said.

“In order to continue on that trend, people need to mask when they’re gathering, they need to get vaccinated and they need to get tested if they’re having symptoms,” Shah said. “We’ve been through this before where we can plateau for a short period of time and then can surge again when people let their guards down.”

As Delta has shown, coronavirus is a threat that just keeps evolving, hence the recent concern over the Mu variant.

Experts agree that in this moment of improving case totals, a new variant is always of great concern, but the one designated with the 12th letter of the Greek alphabet likely will not be the new Delta.

Scripps Research immunologist and molecular biologist Kristian Andersen said Wednesday that the variant, which has gone by the scientific name B.1.162 since it was first detected in Columbia early this year, is less transmissible than the Delta variant that has caused the world’s summer surge. Genetic analysis performed by Andersen’s lab and others shows that the variant the World Health Organization named Mu in early September simply has not shown an ability to outcompete Delta since it first started popping up in the spring.

“Not only do I not think it’s competitive with Delta, I think Delta has it beat pretty much fair and square,” Andersen said, noting that two of the local Mu infections were snow leopards who tested positive for coronavirus infections in late July at the San Diego Zoo.

While the virus remains “one to watch,” the researcher said in an email that the next threat is more likely to come from an already known attacker.

“I think the next variant of real concern will almost certainly be a sublineage of Delta,” Andersen said.

Some might wonder, if Mu has indeed been showing up in lab reports since April, why it has never been included in the county’s now-weekly reports of coronavirus variants.

Shah said that the report only includes those variants officially labeled a concern or of interest by the U.S. Centers for Disease Control and Prevention. So far, the CDC has not yet followed the WHO’s lead in designating Mu a variant of interest or concern.

“We don’t typically report out on a specific variant until the CDC says ‘hey, this is something that we’re concerned about,’” Shah said.

And that’s the case for the vast majority of variation that has been detected in coronavirus samples collected so far. In San Diego County alone, Andersen’s lab and several others have documented 224 distinct viral linages, though only a handful have shown evidence of becoming major public health concerns. Globally, the number of genetically unique types exceeds 1,600.