Delta coronavirus variant: Should fully vaccinated worry?

A couple wears masks and walks next to shops.

July 7, 2021 8:49 AM PT

If you’re fully vaccinated, how worried should you be about the Delta variant of the coronavirus?

There is widespread scientific consensus that fully vaccinated people have an excellent chance of being protected from severe illness or death from any coronavirus strain, including Delta. In Los Angeles County, 99.8% of people who have died from the coronavirus since December have not been vaccinated.

But some health officials, including in Los Angeles County, are now raising questions about whether the Delta variant could be carried by vaccinated people, who then might transmit the virus to those who are unvaccinated.

For fully vaccinated people with the Delta variant, “the big unknown is: Can you become infected — have mild illness — and go ahead and spread that infection to others?” said L.A. County Public Health Director Barbara Ferrer. “We are looking for the answer to that question.”

Without an answer, and given that weekly coronavirus cases in L.A. County have suddenly doubled and COVID-19 hospitalizations have jumped by more than 30%, the L.A. County Department of Public Health last week recommended that even fully vaccinated people resume wearing masks in indoor public areas until more definitive information about the Delta variant emerged.

Federal health officials, by contrast, have said that fully vaccinated people need not wear masks because of the vaccines’ high degree of protection.

The Delta variant is rapidly spreading in L.A. County. For the week that ended June 19, Delta made up nearly 50% of coronavirus cases that were analyzed in L.A. County; four weeks earlier, it accounted for less than 5%.

Here are some questions and answers.

Should you worry about becoming severely ill with the Delta variant?

In places with relatively low rates of coronavirus transmission and high rates of vaccination, there is little risk of a fully vaccinated person becoming seriously ill or dying from COVID-19.

For instance, among 4.5 million vaccinated people in Los Angeles County:

• 0.048% (2,190 people) tested positive for the coronavirus;
• 0.0042% (192 people) were hospitalized for COVID-19;
• 0.0004% (20 people) died of COVID-19.

Who is at higher risk of ‘breakthrough’ infections?

There will always be some “breakthrough” infections, health experts say, in which a virus breaks through the immunity conferred by the vaccine. No vaccine is perfect.

People at higher risk of a vaccine failure include those who have had solid-organ transplants or have a compromised immune system, said Dr. George Rutherford, epidemiologist at UC San Francisco.

Other fully vaccinated people at higher risk of a breakthrough infection are those who have had sustained, intensive exposure to a person sick with COVID-19, for instance a vaccinated parent caring for a coughing, wheezing child.

Experts have said that fully vaccinated people who are in situations where there are high levels of coronavirus transmission — such as during the severe surge in India earlier this year — should still wear masks.

There is widespread scientific consensus on the Delta variant’s infectious potential. Some early estimates of the initial coronavirus strains suggested that every infected person, on average, transmitted the virus to 3.5 others, Rutherford said. Each person with the Delta variant could potentially transmit the virus to more than six people.

Why are some health officials still urging vaccinated people to mask up?

Reacting to rising infection rates, Israel on June 25 reimposed mandatory mask requirements in indoor public spaces, just 10 days after dropping most mask orders.

On the same day, World Health Organization officials — speaking in the context of places with relatively low vaccination rates and places with high rates of coronavirus transmission — said people who were vaccinated should still mask up.

“We still live in a world that is only partially vaccinated that has a lot of susceptibility, a lot of vulnerability. So, what we’re saying is once you’ve been fully vaccinated, continue to play it safe because you could end up as part of a transmission chain,” said Dr. Bruce Aylward, senior advisor to the WHO’s director-general, according to a transcript. “You may not actually be fully protected. Sometimes the vaccines don’t work in people.”

Responding to a question from a reporter in Mexico, Dr. Mariângela Simão, an assistant director-general for the World Health Organization, said that using masks consistently continued to be “extremely important, even if you are vaccinated, when you have a community transmission ongoing — which is the case of Latin America — in general, where you have a high level of continuous community transmission.”

“So,” she said, “people cannot feel safe just because they had” a full course of vaccination: “They still need to protect themselves.”

What’s the latest advice from Dr. Anthony Fauci?

Just last week, Dr. Anthony Fauci, the U.S. government’s top infectious diseases expert, reiterated that the U.S. Centers for Disease Control and Prevention’s recommendation for the nation was “that if you are vaccinated, you have a high degree of protection, so you need not wear a mask either indoor or outdoor.”

He added that local authorities were free to make their own recommendations that differed with the CDC’s based on regional conditions.

Then, speaking on NBC’s “Meet the Press” Sunday, Fauci was asked by host Chuck Todd whether — in a place like Biloxi, Miss., with perhaps one of the lowest vaccination rates in the nation — it would make sense for a fully vaccinated person to still wear a mask.

Fauci said there would be good reason for fully vaccinated people to wear a mask in situations where there were low vaccination rates and higher rates of disease transmission.

“Vaccines are not — even as good as they are and highly effective — nothing is 100%,” Fauci said.

“And if you put yourself in an environment in which you have a high level of viral dynamics and a very low level of vaccine, you might want to go the extra step and say, ‘When I’m in that area where there’s a considerable degree of viral circulation, I might want to go the extra mile to be cautious enough to make sure that I get the extra added level of protection — even though the vaccines themselves are highly effective.’”

Fauci also said it was plausible, but not particularly likely, for a fully vaccinated person to nonetheless become an asymptomatic carrier who could transmit the coronavirus to other people.

Even if the fully vaccinated person becomes infected, he said, they appear to carry less of the virus — so they’re less of a danger to unvaccinated people. If you compare the nasal swab of a fully vaccinated person who is infected but has no symptoms with that of an asymptomatic unvaccinated person, the immunized person has “significantly less” virus.

“So when you look at the level of virus to be lower, that would mean you could make a reasonable assumption that those individuals would be less likely to transmit the infection to someone else,” Fauci said.

The risk is never going to be zero, Fauci said. “But, for the most part, it would be less likely.”

Have other health officials in the U.S. suggested vaccinated people wear masks?

Not many. California officials, and some county officials in the state, have not suggested that vaccinated people return to wearing masks.

In San Francisco, the relaxation of mask requirements is continuing. San Francisco on Tuesday began to allow fully vaccinated guests to stop wearing masks when inside City Hall.

But health officials in the St. Louis, Mo., area on Thursday suggested that fully vaccinated people resume wearing masks — three days after L.A. County made the same recommendation.

“Wear a face covering in indoor public places when other people are present, even if you are vaccinated. We only recommend removing masks when eating and drinking and when you know that others around you are fully vaccinated,” said the advisory from health officials for the city and county of St. Louis.

How do L.A. County and California fare in terms of coronavirus transmission?

The U.S. Centers for Disease Control and Prevention currently ranks California as having a “moderate” rate of community transmission, the second-lowest category on a four-category scale, with about 2.6 new coronavirus cases a day for every 100,000 residents.

Los Angeles County is now averaging 3.8 new coronavirus cases a day for every 100,000 residents, which is in the CDC’s “moderate transmission” category. (At its peak during the winter, L.A. County reported a case rate in excess of 150 new coronavirus cases a day per 100,000 residents — a rate that indicates “high transmission,” the worst category.)

Most counties in California are also in the moderate category, including San Francisco, which is reporting 2.5 new coronavirus cases a day for every 100,000 residents.

Counties in the CDC’s “low transmission” category include San Diego, which is averaging 0.7 new coronavirus cases a day for every 100,000 residents.