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The CDC now advises that people in high-transmission areas wear masks in indoor public spaces, even if they’ve been vaccinated. Why has the Delta variant prompted this change in mask guidance?
Parker: CDC changed their mask guidance because of the evolving nature of SARS-CoV-2 and the rapid spread of the highly contagious Delta variant. New data show there are increasing breakthrough COVID-19 cases in fully vaccinated individuals. Even though breakthrough cases leading to hospitalization or death are rare, new data also show that fully vaccinated individuals who become infected could be contagious and a source of transmission putting immune compromised and unvaccinated people at risk.
Hotez: It has to do with the fact that the amount of virus in the nasal passages and the mouth appear to be higher from Delta compared to previous lineages, and that even if you’re vaccinated and you have some virus-neutralizing antibodies, you could still be asymptomatically shedding virus. But the truth is there’s some new numbers saying even if that’s true, the amount of time you spread the virus may still be very limited, so that you might be shedding viruses for a shorter period of time. But all of this information is still very preliminary and mostly unpublished.
Ultimately, I still think the vast majority of virus transmission is coming from unvaccinated individuals, and that’s why you’re not seeing a big surge in the North. Essentially most, or in some cases almost all, the adolescents and adults are vaccinated, and this has the collateral benefit, whereas with the low vaccination rates among young people in the South, there’s a lot of virus transmission going on.
Under what circumstances would you advise people to wear a mask?
Parker: The CDC guidance advises individuals, unvaccinated and vaccinated, to wear a mask while indoors around other people and where there is high community SARS-CoV-2 transmission. Cases and hospitalizations are surging in many Texas communities. If you live in a community with high transmission, particularly with a surge in hospitalization and ICU cases, I recommend you follow CDC guidance. If you are unvaccinated, you should consider getting vaccinated.
Vaccines are readily available and are by far the most effective tool we have in our toolkit to limit community transmission and reduce the risk of severe disease and death.
Hotez: Clearly, if you’re unvaccinated you should be wearing a mask at all times in indoor settings.
And if you’re vaccinated: I’m still avoiding big indoor crowds, and in which case I’m wearing a mask if I have to be indoors. I don’t go to stores a lot. I’m basically going from work to home most of the time. The only difference now is on the weekends we would take our youngest son and his girlfriend out to dinner and I wouldn’t wear a mask inside the restaurant. Now, with this level of virus transmission, I’m thinking twice about that and starting to go back to DoorDash again.
What do breakthrough infections tell us about the effectiveness of the currently available vaccines?
Parker: To date, the COVID vaccines authorized by the FDA for use in the United States continue to work well, but no vaccine is 100 percent effective. Reports of vaccine breakthrough cases are increasing as new variants emerge and time duration increases from the initial date of completing the vaccination series for many people.
The Phase 3 clinical trial results for Pfizer BioNTech and Moderna vaccines showed 95 percent and 94 percent efficacy against symptomatic COVID-19 illness caused by the original SARS-CoV-2 strains in circulation during the fall of 2020 after two shots. Johnson & Johnson’s vaccine showed 66 percent efficacy against moderate COVID-19 illness and 85 percent efficacy against severe illness after one shot.
The clinical trials did not measure protection against asymptomatic infection or potential to transmit SARS-CoV-2 after vaccination. Nonetheless, the Phase 3 clinical trial results were extraordinary, far exceeded the FDA efficacy threshold of 50 percent, and gave hope that vaccines could control the most severe outcomes of the pandemic.
As of Aug. 9, more than 350 million vaccine doses have been administered and 166 million people were fully vaccinated, 50 percent of the United States population. CDC has received reports of 7,525 hospitalizations or deaths in vaccinated people diagnosed with SARS-CoV-2 infection compared to over 35 million confirmed COVID-19 cases. In about 25 percent of the breakthrough cases, patients were asymptomatic, or their diagnosis appeared secondary to primary cause of hospitalization. This indicates what we knew when the vaccination campaign started and what we know now: vaccine breakthrough cases are expected.
“Vaccines are readily available and are by far the most effective tool we have in our toolkit to limit community transmission and reduce the risk of severe disease and death.”
DR. GERALD PARKER, TEXAS A&M UNIVERSITY
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To date, available data show vaccine breakthrough cases leading to hospitalization or death appear rare and only represent a small percentage of COVID cases. Vaccine breakthroughs are more likely to occur in congregate settings, such as nursing homes, and in populations at risk of vaccine failure (immune compromised, elderly and others).
But CDC’s data has limitations because they are dependent on passive reporting from states on vaccine breakthroughs that led to hospitalization or death and does not include asymptomatic or symptomatic mild to moderate infections.
Population-based studies are needed to gain an understanding of estimated rates of breakthrough cases against mild to moderate infection, vaccine effectiveness against emergency variants, and durability of immunity.
Clinical trials and real-world studies confirm the safety and effectiveness of the Moderna and Pfizer BioNTech COVID vaccines. Through the end of July, the data tells us Pfizer BioNTech and Moderna COVID vaccines remain remarkably effective at reducing risk of hospitalization, severe disease and death for individuals, even for the Delta variant.
Hotez: The vaccines are still really robust. They still give high levels of protection, they’re keeping you out of the hospital and preventing you from symptomatic illness. But there’s increasing information regarding breakthrough cases, and new information in a preprint publication from the Mayo Clinic that protection from non-hospitalized COVID infection may have decreased to the 40-50 percent range for the Pfizer-BioNTech vaccine, with similar data from Israel.
Moreover, when the breakthrough cases happen, they’re associated with higher virus loads. But that’s new information.
We don’t know if this represents true waning immunity versus decreased virus neutralizing antibody against the Delta variant. It’s also important to remember, the way the vaccines were designed was they were tested on their ability to stop symptomatic infection, hospitalization and death, and that mostly still holds. We haven’t lost that, so we should be very mindful that the vaccines still work well.
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