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Coronavirus Delta and Delta Plus Variants Explained

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After reeling under a ravaging wave of the coronavirus, India has finally started limping back to normalcy. The second wave, which peaked in mid-May, seems to be tapering off as of June. However, some warn that there are signs of new concerns being posed by the continuously mutating virus. Scientists working in the field of genomic surveillance have identified multiple cases of a new virulent strain of the SARS-CoV-2 virus - called Delta plus - across the country. Delta plus is a sub-lineage of the Delta variant which is widely believed to be one of the major contributors to the second wave of COVID-19. The article below explains both these variants in detail.

Delta Variant of the SARS-CoV-2

The Delta variant, also called B.1.617.2, is one of the several strains of SARS-CoV-2 that have been designated as “Variants of Concern” by the World Health Organization (WHO) and other organizations. It was first detected in India in October 2020. Since then, it has become the dominant strain in India, the UK, and several other countries.

The Delta variant has some concerning mutations at the spike protein that are not found in other variants. The infection caused by this variant is associated with slightly different primary symptoms than those exhibited by people infected with other variants. Headaches, sore throat, and a runny nose are the most common symptoms experienced by people infected with the Delta variant. On the other hand, cough and loss of taste and smell, are the primary symptoms in cases involving other strains.

Is the Delta variant more transmissible than other variants of SARS-CoV-2?

According to the WHO, the Delta variant is the most infectious SARS-CoV-2 variant yet. It is believed to be nearly 60% more transmissible than the Alpha variant (B.1.1.7) that was first identified in the UK in September 2020. The Alpha variant is itself 50% to 60% more transmissible than the original “wild type” strain that was first detected in Wuhan, China in late 2019. Available scientific evidence suggests that certain key mutations at the spike protein, such as D614G, T478K, L452R, and P681R, may be responsible for the higher transmissibility and infectivity of the Delta variant.

What is the effect of the Delta variant on vaccine efficacy and disease severity?

Scientists say that the Delta variant may partially evade neutralization by antibodies generated by the body after vaccination or a previous bout of COVID-19 infection. A number of real-world observational studies have been conducted to determine the effect of the Delta variant on vaccine efficacy.

  • According to a study by the Public Health England (PHE), a single dose of AstraZeneca vaccine (known as Covishield in India) reduces the risk of COVID-19 infection by the Delta variant by 33%. On the other hand, a single dose of the same vaccine reduces the risk of COVID-19 infection by the Alpha variant by 50%.
  • The same study found that two doses of the AstraZeneca COVID-19 vaccine offer 60% protection against the Delta variant. Contrarily, the vaccine is 67% effective against the Alpha variant.
  • Nevertheless, the study says that the AstraZeneca vaccine is highly effective against the risk of hospitalization from the Delta variant. The two doses of the vaccine likely offer 92% protection against hospitalization by Delta variant.
  • An analysis of breakthrough infections in 100 healthcare workers in India by researchers at the Cambridge University, UK, suggests that the AstraZeneca vaccine may be less effective against infections caused by the Delta variant. It noted that the variant was 8 times less sensitive to vaccine-generated antibodies when compared to the original strain.
  • According to a small study conducted by the National Institute of Virology (NIV), Bharat Biotech, and the Indian Council of Medical Research (ICMR), the indigenously developed COVID-19 vaccine Covaxin offers a lower level of protection against the Delta variant when compared to the original and Alpha strains.

According to researchers, the Delta variant is also associated with an increased risk of severe disease in unvaccinated people. A study published in The Lancet says, when compared to the Alpha variant, the Delta variant doubled the risk of hospitalization in Scotland. Similarly, US CDC states that the variant may render certain life-saving monoclonal antibody treatments less effective.

Delta plus variant

The Delta plus variant, also known as B.1.617.2.1 or AY.1, is a sub-lineage of the Delta variant. It has acquired a key mutation in spike protein - K417N - that was initially found in the Beta variant (first detected in South Africa in 2020). According to scientists, the spike mutation K417N is associated with increased transmissibility, stronger binding to ACE-2 receptors of lung cells, and resistance to monoclonal antibody treatment.

The Delta plus variant has been officially designated a variant of concern by the Health Ministry of India. According to the ministry, the variant has been detected in 48 samples in 10 states from the 45,000 samples sequenced as of end-June. Four people have succumbed to the variant in the country. Besides India, the Delta Plus variant has been detected in several countries all over the world, including the US, UK, Japan, and China.

Challenges posed by the Delta plus variant

The Delta plus variant has been identified recently. Therefore, it is still too early to say whether the Delta Plus variant is more dangerous than the Delta variant or not. Studies are being conducted to determine the effectiveness of vaccines against this mutation. The Indian Council of Medical Research (ICMR) has announced that it will come out with the results of effectiveness trials of vaccines against the Delta Plus variant sometime in July 2021.

The Union Health Ministry has directed the states to step up containment measures, testing, tracking, and vaccination in districts and clusters where the cases of Delta plus variant have been detected. The ministry has also asked these states to immediately send the samples to the designated labs of the INSACOG to aid the genomic surveillance. 


The emergence of the Delta plus variant has sparked fears that it will lead to the third wave of the COVID-19 in the country. The Delta variant played a key role in the worsening of the second wave of the coronavirus. Experts maintain that it is still too early to say if the Delta plus variant is more dangerous than the delta variant. However, the situation will likely evolve as more data becomes available. They recommend ramping up containment measures, testing, tracking, and vaccination in regions where the variant has been detected. People must be sensitized about the significance of getting vaccinated and also following COVID-19 appropriate behaviour, to protect themselves and their loved ones from the new variant.

You can easily consult doctors on the Apollo 24|7 app or website. The online healthcare platform aims to connect you to the best doctors who can help you manage and treat COVID-19 keeping your personal requirements in mind. If you suspect that you might have contracted COVID-19, take the hassle-free Covid self-test from the comfort of your home and get accurate test results within 20 minutes. This easy-to-use Covid self-test kit can be bought online from the Apollo 24|7 app or website.

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