What The Delta Variant Means For COVID-19

The highly contagious Delta variant has caused a surge in COVID-19 infections and hospitalizations, largely among the unvaccinated. This latest development in the coronavirus pandemic has renewed debates about masking, vaccines, and public health protocols as Americans continue to return to offices and schools.

Texas A&M Today spoke about the current state of the pandemic with Dr. Gerald W. Parker, director of the Pandemic & Biosecurity Policy Program within the Bush School of Government and Public Service and associate dean of Global One Health at the College of Veterinary Medicine & Biomedical Sciences, and Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and co-director of the Center for Vaccine Development at Texas Children’s Hospital. At Texas A&M University, Hotez was a 2019-2020 faculty fellow with the Hagler Institute for Advanced Study and is a senior fellow emeritus at the Scowcroft Institute of International Affairs at the Bush School.

What’s your assessment of where we are at this stage of the pandemic in the United States, given the percentage of the population that is fully vaccinated and the surge in COVID-19 infections?

Parker: The SARS-CoV-2 virus continues to move through the population worldwide, adapting with new variants to favor its own survival and continued transmission to vulnerable individuals.

The good news: the biomedical research enterprise and vaccine industry were able to accelerate the development of safe and effective COVID vaccines – without cutting quality, safety, and efficacy corners – in only 11 months after the first genomic sequence of SARS-CoV-2 was published. That was a remarkable public health achievement that was followed by the largest and most complex mass vaccination campaign in public health history. The vaccination campaign was understandably bumpy at first until vaccine production stabilized, healthcare systems vaccinated front-line health care providers at the highest risk of exposure, and state and local authorities geared up mass vaccination sites in urban centers and other means to reach underserved communities and rural areas across Texas and the United States. As vaccine coverage increased from January to May, new daily COVID cases, hospitalizations, and deaths dropped precipitously from their January 2021 highs.

As of Aug. 9, there are have been 407,560,705 vaccines delivered and 351,933,175 vaccine doses administered. Fifty percent of the United States population is fully vaccinated with over 80 percent of the most vulnerable, 65 years of age and older, fully vaccinated.

The bad news: vaccination uptake slowed significantly from May through July, 50 percent of the United States population remains unvaccinated, and a new highly contagious SARS-CoV-2 variant, Delta, emerged in India last spring spreading globally. Delta became the predominant strain circulating in the United States and Texas during the summer of 2021.

During July, the incidence of daily new cases and hospitalizations coinciding with Delta’s emergence has increased rapidly. COVID hospitalizations and ICU cases in Texas are surging. As of Aug. 9, we are 66 percent (9,546) of the peak 14,218 hospitalized patients that occurred in January 2021. Across the United States, hospitalizations are 43 percent of the January peak.

Hotez: We’ve underachieved terribly in vaccinating the South, especially among younger people. When you look at the difference (in vaccination rates) in the North and the South, among those over the age of 65, it’s not that much different: it’s maybe 80 percent versus 95-99 percent (in the North). Where the bottom falls out is among young people.

We’re looking at maybe 20 to 25 percent of adolescents in many Southern counties who are vaccinated, compared to over 70 percent in Massachusetts and Vermont, and similar although somewhat higher percentages among young adults. So the big vulnerability in the South right now is all the unvaccinated young people. And that’s what we’re seeing – COVID-19 is just ripping through the Southern states, and we’re seeing lots of young people going into the hospital now.

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 are 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, 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 the 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 the primary cause of hospitalization. This indicates what we knew when the vaccination campaign started and what we know now: vaccine breakthrough cases are expected.