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  1. Science and Technology Directorate
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  3. Feature Article: Here’s What We’ve Learned About COVID-19—An Update

Feature Article: Here’s What We’ve Learned About COVID-19—An Update

Release Date: September 21, 2021

Much has been said about the pandemic. Scientists all around the world have been laser-focused on studying SARS-CoV-2, the virus that causes COVID-19, for nearly two years and the flood of information can be overwhelming. That’s why a trusted, unified resource that organizes our collective knowledge is so valuable.

The Science and Technology Directorate (S&T)’s Master Question List (MQL) is just that. This consolidation of recent, accurate COVID-19 information is regularly updated with the latest results and data relevant to weathering the pandemic. S&T started publishing the MQL in early 2020 as part of its COVID-19 response.

“The MQL is important for us because it identifies what we don’t know. And with finite lab resources, it ensures we don’t duplicate something that is already being studied elsewhere,” said Dr. Lloyd Hough, director of S&T’s Hazard Awareness and Characterization Technology Center, in S&T’s previous ‘Here's What We’ve Learned About COVID-19’ article. “It’s really a matter of identifying the highest priority gaps—the things that are most impactful for better understanding the disease and helping us to respond to it.”

One current high-priority item is the highly infectious Delta variant, which is now responsible for most new COVID-19 cases in the United States. S&T published the first Delta Variant Supplemental Reference (SR) late last month to quickly summarize key information about it for government decision-makers and the public. The SR is one example of how our nation’s response has had to adapt as the COVID-19 pandemic evolves—which in the case of the Delta variant, is meant quite literally.

We’ve learned quite a bit since last year, but there are still many unknowns as we continue to navigate the national pandemic response. That’s why the MQL is so critical; S&T continues to support the nation’s scientific, medical, and academic communities with a central resource for tracking the most need-to-know information. In the last article, S&T provided asked-and-answered MQL questions that were not only critical for public awareness about COVID-19 but were a testament to the tireless work of our researchers.

The following is a new batch of answers to questions in S&T’s current MQL.

Are there effective vaccines?

According to the U.S. Centers for Disease Control and Prevention (CDC), the vast majority of U.S. COVID-19 hospitalizations (95-99.9%) and deaths (94-99.8%) are occurring in unvaccinated individuals. In the U.S., both Pfizer/BioNTech and Moderna vaccine efficacy has been estimated at 88% overall in a study published by the U.S. National Library of Medicine. Research shows that six months after the first dose of the Pfizer/BioNTech vaccine (in a fully vaccinated person), efficacy is greater than 95% in terms of preventing hospitalization and around 91% in terms of preventing symptomatic infection. Against the Delta variant, the Pfizer/BioNTech vaccine provides 93-96% efficacy against hospitalization and 64-88% efficacy against symptomatic infection, as reported by the New England Journal of Medicine.

The Pfizer/BioNTech, Moderna, and Johnson & Johnson/Janssen vaccines are safe according to extensive data from the CDC and other trustworthy sources. All three vaccines were granted Emergency Use Authorization by the U.S. Food and Drug Administration (FDA) to strengthen our nation’s public health protections during the pandemic crisis. The Pfizer/BioNTech vaccine received full FDA approval in late August. Moderna has completed its submission for full FDA approval and Johnson & Johnson is not far behind.

The FDA has rigorous scientific standards. Thorough evidence of safety and effectiveness from clinical trials with thousands of participants is required for any authorization and continuous monitoring is in place to rapidly detect any issues. The CDC’s tally shows that more than 180 million people in the United States are fully vaccinated.

How does the disease agent compare to previous strains?

The Delta variant of the SARS-CoV-2 virus emerged in India in September 2020, quickly spread to over 100 countries, and now accounts for more than 90% of new COVID-19 cases in the U.S., according to the CDC. The Delta variant is highly transmissible. A study published in the Journal of the Royal Society of London showed an estimated reproduction number (R0) of 5-9, which is far higher than the 2.2-3.1 R0 of the original, wild-type SARS-CoV-2. Another study showed that the Delta variant may lead to higher viral load in infected individuals compared to those with wild-type SARS-CoV-2 or other variants. The viral load of vaccinated individuals with breakthrough Delta variant infection was found by the CDC to be similar to infected, unvaccinated individuals, suggesting that breakthrough cases may be equally capable of transmitting to others.

The CDC has also found that the Delta variant may produce more severe illness and be more likely to cause reinfection—particularly for the unvaccinated. Household secondary attack rates of the Delta variant can be as high as 53% and may be higher in individuals younger than 10 years old. Early evidence published by the British Medical Journal suggests that the Delta variant spreads rapidly in schools.

Are there tools to diagnose infected individuals?

Diagnosis of COVID-19 is based on symptoms consistent with COVID-19, polymerase chain reaction (PCR)-based testing of active cases, and/or the presence of SARS-CoV-2 antibodies in individuals. Screening solely by temperature or other symptoms is unreliable. Nasopharyngeal swabs are the gold standard for COVID-19 diagnosis.

PCR is a method widely used to rapidly make millions of copies of a specific DNA sample. The timing of diagnostic PCR tests impacts results. As reported in the American College of Physicians (ACP) Journal, Annals of Internal Medicine, the false-negative rate is lowest between 7 and 9 days after exposure. PCR tests are more likely to give false-negative results before symptoms begin (within 4 days of exposure) and more than 14 days after exposure.

What are the long-term symptoms of COVID-19 infection?

Post-Acute Sequelae of SARS-CoV-2 (PASC) infection, also known as “long-haul COVID” or simply “long COVID”, affects 5-10% of patients and is a persistent infection lasting longer than four weeks. Another ACP study showed fatigue, loss of taste or smell, shortness of breath, and headache are the most common chronic symptoms and they can persist for months. Neurological impairment has also been reported and may affect the patient’s ability to return to work.

How easily is it spread?

Worldwide, COVID-19 has caused at least 225 million infections and claimed over 4.6 million lives. The U.S. alone has seen over 42 million cases and more than 670,000 deaths. These and other statistics are available via the Johns Hopkins University COVID-19 Dashboard.

COVID-19 has reportedly spread to numerous animals both in the wild and in captivity, including otters, deer, mink, ferrets, gorillas, tigers, and lions—though there doesn’t seem to be evidence of transmission to humans in these cases.

What personal protective equipment is effective, and who should be using it?

The CDC asserts that face masks are effective at reducing transmission of COVID-19. Numerous studies have supported this finding, including research published by the American Society for Microbiology (PDF, 5 pgs., 1.62MB), the Journal of the American Medical Association, and Nature Research. Wearing a mask protects others as well as yourself. Updated CDC guidance states that in general, mask-wearing is not necessary in outdoor settings. For the unvaccinated, or if COVID-19 cases are high in the area, mask-wearing in crowded outdoor settings should be considered. Wearing a mask in indoor public places maximizes protection. To be effective, a face mask must fully cover the nose and mouth; masks should fit snugly against the sides of the face and not have gaps.

There is a path forward.

Not a question, but a final note of hope and encouragement: we have made great strides in conquering this crisis, though plenty remains to be done. There are a number of recommended treatments depending on disease severity, but none of them are a guarantee of recovery. The best thing we can all do is follow the recommendations of the CDC and our local public health authorities.

“I urge anyone who is concerned about their health and the health of their loved ones from COVID-19 to refer to CDC’s guidance, to talk to their doctor, and to educate themselves using official, trustworthy scientific sources,” added Dr. Hough. “We’re doing the science to help keep people safe, and it is incumbent upon all of us to do our part and stay informed.”

If you’d like to learn more about any of the science presented here, check out the MQL or the new Delta Variant SR. You can find comprehensive public health guidance on the CDC website. For related media requests, contact STMedia@hq.dhs.gov

Last Updated: 09/21/2021
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