With a wave of new coronavirus cases, will it soon be masks up in San Diego?

With a wave of new coronavirus cases, will it soon be masks up in San Diego?

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Unlike Los Angeles County, San Diego has not reinstated an indoor mask mandate for all residents, regardless of vaccination status. But exploding local case rates are making many wonder whether it’s just a matter of time.

After a mid-week update from the county health department showed that daily case totals are now essentially where they were in mid-July of 2020, the situation grew even more dramatic Friday with an announcement that more than 1,200 positive test results were received Thursday.

Despite the full vaccination of nearly 2 million San Diegans — nearly 70 percent of all who are eligible — it’s the largest single-day number since Feb. 5, and nearly double Wednesday’s count.

For the moment, the number of hospitalizations related to COVID-19 remains lower than it was one year ago, despite the similar new case volume. But it can take weeks for a new infection to grow severe enough to require a hospital stay, so the region’s healers are bracing for further increases in coming weeks.

At Hillcrest a passenger onboard the MTS bus wears a face mask while riding down University Avenue.

In Hillcrest a passenger on board a bus wears a face mask while riding down University Avenue. According the Metropolitan Transit System website, as of June 2021, all passengers are still required to wear face coverings on board (even if fully vaccinated) .

(Nelvin C. Cepeda/The San Diego Union-Tribune)

The state’s best estimates of the virus’s current effective reproductive number — often called R-effective — hit 1.35 across California this week after months under one. This metric estimates the number of people an infected person will spread the virus to, and a value greater than one means that a community is on track for an exponential increase in cases. San Diego County’s latest number is 1.54, slightly higher than the state average. The R-effective in Los Angeles County is 1.37.

It is a situation that surely gets many thinking about what public health officials said on June 15 when the state’s tiered reopening system ended and the state dropped its universal masking mandate, adopting federal guidance that only the unvaccinated need to cover up but that the fully vaccinated can visit stores, entertainment venues and most other places mask-free.

When restrictions loosened, leaders at all levels said they would continue to monitor the numbers daily to determine if changes needed to be made. But they never specified just how high is too high for measures like test positivity rate, effective reproduction rate or hospitalization rate.

Asked for more clarity this week, the California Department of Public Health declined to get specific, stating only that it “continues to closely monitor the spread of COVID-19 and its variants” and noting that local health departments are free to “put into place policies that are more strict than state guidance” if they wish.

Dr. Wilma Wooten, San Diego County’s public health officer and director, did not respond to a request for comment on what would prompt her to order San Diegans to pull those masks back up. The county’s list of 13 COVID-related triggers, though, tells its own tale. For the first time in months, four items on the list — local case rate, the number of recent community outbreaks, growth in the pace of hospitalizations and the speed of contact tracing investigations — are all in the red, indicating they’ve crossed over into concerning territory.

Some researchers say it’s already time to bring back indoor masking — and that the CDC’s initial guidance for fully vaccinated people was too hasty as it gave the unvaccinated an opportunity to quietly shed their masks, too.

“It was all premature, and I think that it wasn’t in line with what public health communications experts would have advised,” said Corinne McDaniels-Davidson, an epidemiologist at San Diego State University. “When you take your foot off the gas, what happens is what you would expect to happen — you slow down.”

UC San Diego chief of infectious disease research Dr. Davey Smith wasn’t as critical of the initial CDC guidelines, noting that the agency’s stance may have encouraged some people to get their shots. But he, too, says it’s only a matter of time before indoor masking returns to San Diego given current trends.

“In the best-case scenario, I would have liked to see a little uptick after July the Fourth, followed by a little bit of an uptick of hospitalizations, but, by now, our number of new infections would actually be going down,” Smith said. “Unfortunately, I’ve only seen the number of new infections continue to go up. And that concerns me.”

Though many remain skeptical about whether masking was really ever that effective at slowing the pandemic, the science is increasingly clear that cloth face coverings can significantly slow transmission.

Meinrat O. Andreae, a renowned chemist at the Scripps Institution of Oceanography whose research focuses on how aerosols — fine particles suspended in air — affect climate, co-authored a study published in the journal Science in May that attempts to quantify the effects of cloth masks on coronavirus transmission.

Noting that many studies have now documented that face coverings have reduced transmission in the real world, the study finds that, while cloth face coverings only filter out between 30 percent and 70 percent of the respiratory droplets that carry coronavirus, they can nonetheless be very effective at reducing transmission in situations where large concentrations of virus do not linger in the air.

Masks, Andreae noted, tend to be best at snagging the larger droplets dislodged when a person coughs or sneezes and less effective at blocking the very fine particles that propagate when people speak and even breathe.

The key, he added, is understanding that one or two or even 10 or 100 virus particles are generally not enough to cause an infection. It takes thousands of particles to overwhelm the body’s natural defenses, and research shows that not every droplet contains virus. That means that even an imperfect filter can have a protective effect as long as the amount of airborne particles is not very high.

“We don’t need to cut it by 100 percent; we just need to cut it enough so that whatever still makes it past the mask is a small enough amount to be dealt with by your body’s natural defenses,” Andreae said.

This is why location is everything. Wide-open, well-ventilated spaces are much less likely to build up that critical level of tiny water droplets capable of lingering in the air than closed-in poorly-ventilated spaces.

“Think cigarette smoke,” he said. “If you’re walking down the beach, and there are one or two people somewhere smoking, you might get a whiff of it, but you’re not going to get seriously exposed.

“If you think of a bar, back when they allowed smoking, you go in there, and you’re going to inhale a serious amount of second-hand smoke.”

Though he said he is fully vaccinated, Andreae said he continues to put on a mask indoors unless he is 100 percent certain that all present are vaccinated, and he will generally leave his face uncovered outdoors. He continues to skip indoor restaurant invites.

Why bother with masks if he is vaccinated?

“While you, if you are fully vaccinated, may only become mildly sick if you are infected, you also, then, become a spreader of the virus,” he said. “That’s not such a good thing because you don’t know who you’re going to end up spreading it to.

“You may spread it to someone who is immunocompromised, you may spread it to somebody who’s not vaccinated and cause them to become seriously ill.”

Natasha Martin, an infectious disease modeler at UC San Diego, is looking at how masking could impact UCSD’s infection rates. She says preliminary models show that masking would substantially limit the virus’s spread at the university.

“The majority of the benefit comes from masking of unvaccinated individuals,” she said in an email.

Without constantly verifying each person’s vaccination status, it’s difficult to ensure the unvaccinated mask up without requiring everyone to do so. Martin didn’t elaborate on the size of the dip in transmission shown by her model or the rate of masking she’s assuming, and she has yet to run the same analysis for San Diego County. But she stressed that masking while continuing to vaccinate as many people as possible, as quickly as possible, will save lives.

“The sad thing is that most of the deaths we will see in the coming months will have been preventable,” Martin said.

The Delta variant may be twice as transmissible as the virus first identified in Wuhan, China, according to a report in May from the United Kingdom Scientific Advisory Group for Emergencies. And publicly available sequencing data suggest that the variant is responsible for 75 percent or more of new infections in California.

The good news: Fully vaccinated people are largely protected against the various coronavirus strains, and breakthrough infections have been relatively rare and mild. But the unvaccinated population is still large enough that we could see a sizable surge — even if it’s not as bad as last winter.

“Because we saw such terrible devastation in the winter, people’s frame changed, and, so long as it doesn’t get that bad again, it’s almost acceptable,” McDaniels-Davidson said.

Another looming concern is that the longer the virus mutates and evolves, the greater the odds that it’ll finally generate a variant that vaccines don’t work against.

The best way to prevent that hasn’t changed over the past several months, says Smith.

“Don’t be scared of the Delta variant if you’re vaccinated. If you’re not vaccinated, then you should be scared. And that means to go get vaccinated.”



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