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What’s the Deal with the Delta Variant?

Updated: Jul 8

"The Delta variant is currently the greatest threat in the U.S. to our attempt to eliminate COVID-19.” - Anthony Fauci, M.D., Director, U.S. National Institute of Allergy and Infectious Diseases


“I will say, as worrisome as this delta strain is with regard to its hyper-transmissibility, our vaccines work.” - Rochelle Walensky, M.D., Director, U.S. Center for Disease Control and Prevention



For we Americans that have been vaccinated against COVID-19, this year’s Independence Day brought a sense of relief that we were protected against severe COVID-19 and again able to celebrate the Fourth of July with friends and family. But a nagging question remains: “What about the Delta virus variant?” According to the Axios-Ispos Coronavirus Index, at the end of June 72% of U.S. adults were concerned about this variant, with 36% extremely concerned and 36% somewhat concerned. Thus, in this Germ Gems post I focus on the Delta variant and discuss who should be most concerned about its increasingly dominant role in the COVID-19 pandemic.

What is the Delta variant? Since this pandemic began more than a year-and-a-half ago, variants (mutations) of SARS-CoV-2 have been popping up. I’ve featured several of these variants in earlier Germ Gems posts. You may recall reading in my May 19, 2021 post, “Vaccines vs. Variants: A Marathon Not a Sprint,” that the World Health Organization (WHO) and the Center for Disease Control and Prevention (CDC) have flagged four so-called variants of concern (VOC), that is, variants that they’ve identified “for which there is evidence of an increase in transmissibility, more severe disease, e.g., increased hospitalizations or deaths, significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection and failures.” Moreover, the WHO and the CDC recently changed the system for classifying variants from numbers to a designation based on Greek letters. The four VOCs, in order of their official recognition in the U.S. by the CDC, are: Alpha (first detected in the U.S. in December 2020); Beta (first detected in the U.S. at the end of January 2021); Gamma (first detected in the U.S. in January 2021); and Delta (first detected in the U.S. in March 2021).


Delta entered America like gangbusters. In the two weeks ending May 22, Delta made up just 2.8% of all cases in the U.S. By June 5, just two weeks later, its share jumped to 9.5%. And on June 19, again just two weeks later, it was estimated that Delta accounted for 20.6% of all cases. According to the CDC’s mapping tool, Delta is currently most prolific in the central and western parts of the U.S. In Montana, Wyoming, Colorado, Nebraska, and surrounding areas, Delta now accounts for over 47% of all cases. Some experts predict that Delta will become the dominant SARS-CoV-2 variant in the U.S. in the next two to three weeks.


At the same time that the Delta variant is sweeping through America, it’s also on track to become the dominant cause of COVID-19 globally. It has precipitated new lockdowns in the UK, Australia, and several Asian countries. According to the WHO regional director in South Africa “the speed and scale of Africa’s third wave is like nothing we’ve seen before.”


Pathogenesis of the Delta variant. The underlying basis for the Delta variant’s highly successful onslaught worldwide is yet to be established. According to research carried out at Georg-August-University in Gottingen, Germany, once in the lungs, the Delta variant breaks into cells and fuses them together which allows it to spread faster and to partially hide from the immune system by evading antibodies.


It appears that a gene-based alteration in the SARS-CoV-2’s spike protein (the knobby structures on the viral surface that bind to ACE2 receptors on host cells and trigger cell entry) facilitates infection of cells in the lung and that this in turn somehow results in increased transmissibility of the virus. According to an article in Science on June 25, “Delta variant triggers new phase in the pandemic,” when compared with the Alpha variant, Delta results in 50% to 100% more transmission. And according to the head of the WHO, the Delta variant is “the most transmissible of the variants so far.”

Delta variant exploits low vaccination rates. A striking correlation is seen throughout the world between the risk of infection by the Delta variant and low vaccine rates. In America, about 47% of the population is fully vaccinated. On July 1, the director of the CDC commented, “Looking across the country we have made incredible progress. However, looking state by state and county by county it is clear communities where people remain unvaccinated are communities that are vulnerable.” Almost all U.S. COVID-19-related deaths currently occur in unvaccinated people, and it’s likely that mortality associated with the Delta variant will follow suit. Therefore, to prevent fatal infection by the Delta variant, people need to get vaccinated.


Sadly, in America the approach to the COVID-19 pandemic is politicized. In an article in US News in June, “‘Two Americas’ may emerge as Delta variant spreads and vaccination rates drop,” researchers warned that a picture of “two Americas” is emerging—the vaccinated and the unvaccinated—reflecting red state (Republican) and blue state (Democratic) political divides. Peter Hoetz, a vaccine researcher at Baylor College of Medicine in Houston calls it “two Covid nations.”


While the Delta variant is clearly more transmissible, we don’t know yet whether it’s also more virulent, that is, if it inflicts greater organ damage and death. Preliminary epidemiological work from England and Scotland suggested that Delta may be more virulent (assessed by increased risk of hospitalization when compared to the Alpha variant). But according to data released by Public Health England on July 1, the Delta variant is not driving a surge in hospitalizations in England.


What about the other variants? Most of the attention of COVID-19 epidemiologists is focused at present on the Delta variant. Nonetheless, we shouldn’t forget the other VOCs. In a MedPage Today article on July 2, “The Gamma Variant’s Rise in Washington State: New data show COVID strain associated with the highest number of hospitalizations, deaths,” researchers in the state of Washington provide evidence that while the Delta variant is causing an increased number of infections, the Gamma variant is more aggressive, that is, it causes more hospitalizations and deaths.


Finally, as if the plain old Delta variant isn’t wreaking enough havoc around the world, a closely related new variant dubbed “Delta Plus” recently emerged in India. This Delta variant cousin carries a mutation (K147N) that is present in the Beta variant first identified in South Africa. As of June, at least 197 cases had been reported from 11 countries. While India declared Delta Plus (K417N) a VOC, neither the WHO nor CDC has done so…yet.


If you’re vaccinated, are you protected against the Delta variant? The good news is that if you’ve been fully vaccinated with any of the vaccines with Emergency Use Authorization by the U.S. Federal Drug Administration (that is, the two-dose mRNA vaccines from Pfizer/BioNTech or Moderna, or the one-shot adenovirus-vectored Johnson & Johnson vaccine), you’re likely protected against severe disease caused by the Delta variant as well as by the Alpha, Beta, and Gamma variants. Because of an uptick of COVID-19 cases due to the Delta variant in Israel, where more than 60% of the population is fully vaccinated with the Pfizer/BioNTech vaccine, the question arises, “Should I get a booster shot?” While boosters have been shown to work well, most experts suggest we don’t need them yet. Despite the apparent decline in the vaccine’s effectiveness in Israel, the Israeli government continues to encourage vaccination but they continue to monitor the situation carefully. So for now in the U.S., if you’re vaccinated, I wouldn’t worry.


Should vaccinated people still wear masks? The Delta variant has spurred intense debate on whether masks should still be used to prevent COVID-19 in vaccinated people. While the WHO urges fully vaccinated people to continue to wear masks, the CDC stands by its advice that fully vaccinated Americans do not need to wear masks in most situations. The case for wearing masks is based on concerns arising from the experience in hot spots in the world where high levels of vaccination don’t seem to prevent outbreaks of Delta variant infection, such as, Israel. In the U.S., recommendations regarding mask wearing vary by location. L.A. County, for example, recommends that everyone, even if vaccinated, wear masks indoors. This seems reasonable, just as does continuing to keep social distancing in crowded indoor spaces.

Optimizing vaccine deployment. As suggested earlier, the Delta variant is causing dense outbreaks of COVID-19 in states with low vaccination rates. While the 47% of the U.S. population that has been fully vaccinated against SARS-CoV-2 has little to worry about, fewer than 35% of people living in Alabama, Arkansas, Louisiana, Mississippi, and Wyoming are fully vaccinated. As pointed out by correspondent Shannon Firth in an article in the July 1st MedPage Today , “House Lawmakers Eager to Boost Vaccine Uptake, Quash Hesitancy,” a number of strategies, such as, pre-scheduled appointments, cash payments, and lotteries are in play to increase vaccinations. Also on July 1, the White House launched “surge response” teams to Delta variant hot spots. These multidisciplinary “strike teams” are being dispatched to 1,000 counties where the Delta variant is spreading rapidly.


About 30% of Americans are “COVID vaccine holdouts.” Nonetheless, the increased efforts of both Public Health practitioners and primary care doctors to encourage vaccination may still pay off, that is, the U.S. will reach the goal of “herd immunity” (80% community immunity to SARS-CoV-2 by vaccination or natural infection). The question is: when?


A more daunting challenge is achieving broad vaccine coverage in low- and middle-income countries (LMICs). But even in this arena, there’s some room for optimism. For example, the recent announcement of plans for the first African COVID Vaccine Production Hubs is considered “revolutionary.” Similarly, in a July 1 article in the Journal of American Medical Association, “Sharing Technology and Vaccine Doses to Address Global Vaccine Inequity and End the COVID-19 Pandemic,” plans are in development to share technology and expand manufacturing capacity, waive intellectual property, and reallocate procured vaccine doses.


To date, one of the most important lessons learned during the COVID-19 pandemic is that vaccines against SARS-CoV-2 work! They even provide protection against the variants. So far, only four of the 24-letter modern Greek alphabet have been needed to address SARS-CoV-2 VOCs. The grand challenge now is to accelerate vaccination programs throughout the world before we march any closer to the last letter, Omega.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

 

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