New Threats: An Overview of the Delta and Delta Plus Variants of the Virus Causing COVID-19
Updated: Sep 7, 2021
Catherine Gan, Morristown High School, Morristown, New Jersey, USA
The COVID-19 pandemic has caused millions of deaths and pushed healthcare systems around the world to their limits. As of August 15, 2021, there have been 207,906,437 COVID-19 cases and 4,373,339 deaths globally (Worldometer, 2021). COVID-19 is caused by the SARS-CoV-2 virus, and recently, a more virulent COVID-19 variant, the Delta variant, has come to the center of global attention.
There are several variants that the World Health Organization (WHO) has classified into two levels of increasing importance: variant of interest and variant of concern (WHO, 2021). Variants of interest, such as Eta, Iota, Kappa, and Lambda variants, are currently not widespread but could lead to outbreaks. Variants of concern, which include Alpha, Beta, Gamma and Delta variants, have increased transmission rates and disease severity and decreased effectiveness of vaccines against them. The Alpha (B.1.1.7) variant was identified in the United Kingdom in September 2020. In May 2020, the Beta (B.1.351) variant was detected in South Africa. The Gamma (P.1) variant was discovered in Brazil in November 2020. The Delta (B.1.617.2) variant, identified in India in October 2020, recently made headlines and has become the dominant strain in the United States, United Kingdom, and many other countries (CDC, 2021).
The Delta variant spreads faster and is more deadly than previous variants (CDC, July 13, 2021). The variant has mutations on its spike proteins which better enable it to infect cells. Consequently, it is 50% more transmissible than the Alpha variant, which is 50% more contagious than the original virus (Bever, 2021). Its symptoms are similar to that of the original COVID-19 strain. Some people have mild symptoms, while others have more severe reactions and could become seriously ill, especially if their immunity is weakened. The symptoms may appear within 2 to 14 days after exposure, and may include fever/chills, difficulty breathing, body aches, muscle aches, fatigue, loss of taste or smell, cough, congestions/runny nose, headache, sore throat, diarrhea, and nausea (CDC, February 22, 2021). However, there are reports from the United Kingdom that cough and loss of smell seem to be less common among those infected by the Delta variant (Zoe, 2021). Children could additionally experience severe inflammation known as multi-system inflammatory syndrome (MIS-C). MIS-C is a serious COVID-19 complication where multiple organs in the body, such as the lungs, heart, kidneys, gastrointestinal organs, skin, eyes and brain, become inflamed (CDC, February 24, 2021). A study in the United Kingdom found that children and adults under 50 are 2.5 times more likely to succumb to the Delta variant, with most infections occurring in the unvaccinated group (Riley, 2021).
A sub-variant of the Delta strain has also appeared: the Delta Plus variant (B.1.617.2.1 or AY.1). This strain has been reported in 11 countries and declared to be a variant of concern by the United Kingdom government agency Public Health England (Jeong, 2021). This variant has an additional mutation, K417N, in its spike protein that makes it easier to infect cells, increasing transmissibility, allowing stronger binding to the lung cell receptors, and potentially decreasing monoclonal antibody response (Jeong, 2021).
The available COVID-19 vaccines have been effective against the Delta variant at preventing severe disease and hospitalizations. The Public Health England (not peer-reviewed) analysis showed the Pfizer-BioNTech vaccine and the Oxford-AstraZeneca vaccine to be 96% and 92% effective against hospitalization, respectively, after two doses (Public Health England, 2021). These percentages are comparable to the protection against the Alpha variant (B.1.1.7). Oxford-AstraZeneca is also known as Covishield in India. A study in Scotland found the Pfizer-BioNTech vaccine to be 79% effective in preventing infection after two doses (Sheikh, 2021). Another study showed a single dose of Pfizer-BioNTech vaccine to be 36% effective against symptomatic disease and 88% effective after two doses, while Oxford-AstraZeneca vaccine is 30% effective after one dose and 67% effective after two doses (Bernal, 2021). A study published in Nature found that one dose of Pfizer-BioNTech or AstraZeneca vaccine is barely effective against the Delta variant, while two doses result in neutralizing responses from 95% of individuals (Planas, 2021). A Canadian study (not peer-reviewed) found Pfizer-BioNTech, Moderna, and AstraZeneca vaccines to be 56%, 72% and 67% effective against symptomatic infection respectively after one dose, and Pfizer-BioNTech vaccine to be 87% effective after two doses (Nasreen, 2021). These results affirm the importance of completing the two dose vaccination series.
Another study with the Moderna vaccine (not peer-reviewed) investigated if serum from participants vaccinated with the Moderna vaccine could neutralize pseudovirus containing Delta variant spike protein mutations (Choi, 2021). They found that antibodies from those participants neutralize the pseudovirus. A clinical trial with the Johnson and Johnson vaccine indicated that the vaccine is 85% effective against severe disease at least 28 days after vaccination, and that it induces antibody activity that neutralizes the virus from infecting cells (Sadoff, 2021). Another study showed that Johnson and Johnson vaccine neutralizes the virus with increased neutralizing antibody responses over time (Barouch, 2021). Currently, there is limited data on the effects of other COVID-19 vaccines against the Delta variant. A small study indicated that antibodies from participants vaccinated with the Covaxin vaccine could neutralize the Delta variant (Yadav, 2021). At this time, there are insufficient data on the effectiveness of vaccines against the Delta Plus variant.
New variants will keep emerging as the coronavirus mutates. Fortunately, existing vaccines are effective against the variants thus far. Studies have also shown the importance of completing the series of vaccinations for two-dose vaccines. Vaccination plays a major role in bringing the pandemic to an end. With the Delta variant spreading worldwide, it has become crucial to vaccinate the population as quickly as possible to prevent further spread and the emergence of additional variants.
Barouch, D. H., Sadoff, J., You, J., Gars, M. L., Heerwegh, D. & Douoguih, M. (2021, July 14). Durable humoral and cellular immune responses 8 months after Ad26.COV2.S vaccination. The New England Journal of Medicine. Retrieved July 22, 2021, from https://www.nejm.org/doi/full/10.1056/NEJMc2108829
Bernal, J. L., Andrews, N., Gower, C. et al. (2021, July 21). Effectiveness of COVID-19 vaccines against the B.1.617.2 (Delta) Variant. The New England Journal of Medicine. Retrieved July 22, 2021, from https://www.nejm.org/doi/full/10.1056/NEJMoa2108891
Bever, L. & Achenbach, J. (2021, July 9). What you need to know about the highly contagious delta variant. The Washington Post. Retrieved July 22, 2021, from https://www.washingtonpost.com/health/2021/07/07/delta-variant-covid/
CDC Center for Disease Control and Prevention. (2021, February 22). Symptoms of COVID-19. Retrieved July 22, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html
CDC Center for Disease Control and Prevention. (2021, February 24). Multisystem Inflammatory System. Retrieved July 22, 2021, from https://www.cdc.gov/mis/mis-c.html
CDC Center for Disease Control and Prevention. (2021, July 13). SARS-CoV-2 Variant Classifications and Definitions. Retrieved July 22, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/variants/variant-info.html#print
CDC Center for Disease Control and Prevention. (2021). COVID data tracker. Retrieved July 22, 2021, from https://covid.cdc.gov/covid-data-tracker/#global-variant-report-map
Choi, A., Koch, M., Wu, K., Dixon, G., Oestreicher, J., Legault, H., Stewart-Jones, G. B. E., Colpitts, T., Pajon, R., Bennett, H., Carfi, A. & Edwards, D. K. (2021, June 28). Serum Neutralizing Activity of mRNA-1273 against SARS-CoV-2 Variants. BioRxiv. Retrieved July 22, 2021, from https://www.biorxiv.org/content/10.1101/2021.06.28.449914v1.full.pdf
Jeong M. (2021, July 6). Delta plus variant of SARS-CoV-2: How does it compare with the delta variant? Medical News Today. Retrieved July 22, 2021, from https://www.medicalnewstoday.com/articles/delta-plus-variant-of-sars-cov-2-how-does-it-compare-with-the-delta-variant
Nasreen, S., He, S., Chung, H., Brown, K. A., Gubbay, J. B., Buchan, S.A., Wilson, S. E., Sundaram, M. E., Fell, D. B., Chen B., Calzavara, A., Austin, P. C., Schwartz, K. L., Pharm M. T., Wilson, K. & Kwong, J. C. (2021, July 3). Effectiveness of COVID-19 vaccines against variants of concern, Canada. Medrxiv. Retrieved July 22, 2021, from https://www.medrxiv.org/content/10.1101/2021.06.28.21259420v1.full.pdf
Planas, D., Veyer, D., Baidaliuk, A., Staropoli, I., Guivel-Benhassine, F., Rajah, M. M., Planchais, C., Porrot, F., Robillard, N., Puech, J., Prot, M., Gallais, F., Gantner, P., Velay, A., Guen, J. L., Kassis-Chikhani, N., Edriss, D., Belec, L., Seve, A., Courtellemont, L., Pere, H., Hocqueloux, L., Fafi-Kremer, S., Prazuck, T., Mouquet, H., Bruel, T., Simon-Loriere, E., Rey, F.A. & Schwartz, O. (2021, July 8). Reduced sensitivity of SARS-CoV-2 variant Delta to antibody neutralization. Nature. Retrieved July 22, 2021, from https://www.nature.com/articles/s41586-021-03777-9
Public Health England. (2021, June 14). Vaccines highly effective against hospitalization from Delta variant. Retrieved July 22, 2021, from https://www.gov.uk/government/news/vaccines-highly-effective-against-hospitalisation-from-delta-variant
Riley, S., Wang, H., Eales, O., Haw, D., Walters, C., Ainslie, K., Atchison, C., Fronterre, C., Diggle, P., Page, A., Prosolek, S., Trotter, A. J., Le Viet, T., Alikhan, N. F., The COVID-19 Genomics UK Consortium, CPG-UK, Ashby, D., Donnelly, C., Cooke, G., Barclay, W., Ward, H., Darzi, A. & Elliott, P. (2021, June 17). REACT-1 round 12 report: resurgence of SARS-CoV-2 infections in England associated with increased frequency of the Delta variant. Retrieved July 22, 2021, from https://spiral.imperial.ac.uk/bitstream/10044/1/89629/10/react1_r12_preprint_final.pdf
Sadoff, J., Gray, G. & Vandebosch, A. et al. (2021, June 10). Safety and efficacy of single-dose Ad26.COV2.S vaccine against Covid-19. The New England Journal of Medicine, 384: 2187-2201. Retrieved July 22, 2021, from https://www.nejm.org/doi/full/10.1056/NEJMoa2101544
Sheikh, A., McMenamin, J., Taylor, B. & Robertson, C. (2021, June 26). SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness. The Lancet, 397(10293), 2461-2462. Retrieved July 22, 2021, from https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01358-1/fulltext
WHO World Health Organization. (2021, July 6). Tracking SARS-CoV-2 variants. Retrieved July 22, 2021, from https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/
Worldometer. (2021, August 15). Covid-19 coronavirus pandemic. Retrieved August 15, 2021, from https://www.worldometers.info/coronavirus/
Yadav, P. D., Sapkal, G.N, Abraham, P., Ella, R., Deshpande, G., Patil, D. Y., Nyayanit, D. A., Gupta, N., Sahay, R. R., Shete, A. M., Panda, S., Bhargava, B., Mohan, K. (2021, April 23). Neutralization of variant under investigation B.1.617 with sera of BBV152 vaccines. Biorxiv. Retrieved July 22, 2021, from https://www.biorxiv.org/content/10.1101/2021.04.23.441101v1
Zoe Covid Symptom Study. (2021, May 12). COVID infection & vaccination rates in the UK today. Retrieved July 22, 2021, from https://covid.joinzoe.com/data
Article Thumbnail: Coronavirus (Covid-19). (2020, March 20). Retrieved July 22, 2021, from https://search.creativecommons.org/photos/6f5e7d78-bf4e-4b46-8ba9-c469af85860f