The year 2019 witnessed the beginning of one of the worst possible pandemics of the earth in the form of coronavirus. First reported in the Wuhan city of China in the month of December in an open-air market and spread rapidly in the whole world. With the progress of the coronavirus pandemic, various variants of the initial coronavirus have appeared. Some of them have resulted in an increase in the number of infections due to their dominant nature while some were unable to change the trajectory of the coronavirus pandemic.

Here, we will talk about one of the variants of coronavirus, the Delta variant.


At the end of 2020 in India, the Delta variant was first time identified that then rapidly spread and became the most infecting variant in India and Great Britain before its rapid emergence in the United States. Until the middle of December 2021, this variant had been the most dominant variant causing coronavirus infection globally accounting for almost 99% of the cases at that time. Delta variant has also been a major cause of hospitalizations in many countries (1).

WHO has declared the delta variant as a “variant of concern” because the transmissibility of the delta variant is high, it can cause severe infection that can lead to hospitalization or can result in death. The variant of concerns also can significantly reduce the neutralizing action of the antibodies that were developed due to vaccination or previous coronavirus infection. It also decreases the efficacy of the vaccines or treatment and can also cause failure in diagnostic detection (2).


The likelihood of mutation in a virus increases when it circulates widely and results in numerous infections. The more opportunities a virus gets to spread, there are more chances for it to change. Sometimes, due to these changes, a viral variant gains a better ability of growth in the human cells leading to greater quantities of viruses being produced. The efficiency of viruses for transmitting to other people increases to higher levels.

The transmissibility of the delta variant is almost 50% greater than its alpha variant (originally emerged first time in the United Kingdom). The delta variant is almost 50% more transmissible than the original strain of the coronavirus first time identified in Wuhan. A study reported that the mouth and nose of the people infected with the delta variant carry almost a thousand times more quantity of the virus than the people who were infected with the original strain (3). This shows that transmissibility will be easier when there is more virus.

It is estimated that in an environment that is completely unmitigated, where no one wears masks or is vaccinated, the original strain of coronavirus infecting an average person will spread to almost 2.5 other people. However, the delta variant may spread to 3.5 to 4 people in the same conditions.


The risk of infection with coronavirus increases for those who are unvaccinated and also for the young population as the older people get vaccinated. Due to its high transmissibility, the delta variant is a concern for children and teenagers. A study conducted in the United Kingdom reported that there are 2.5 times more chances of children and adults aged less than 50 years contracting delta variant (4).


The usual symptoms reported due to an infection from coronavirus include high-grade fever, persistent cough, a change or loss of sense of taste and smell with or without difficulty in breathing. But according to the ZOE COVID SYMPTOM STUDY, people have reported that they have experienced slightly different symptoms. More common symptoms include runny nose, headache, fever, and sore throat while less common symptoms include loss of smell and cough (5).


One of the concerns raised with the spread of delta variant was for the low-vaccinated areas. The highly vaccinated areas make pockets around those places adjacent to them having 20% of the vaccination. Because of this, the virus is allowed to move from one poorly vaccinated vicinity to another. When high vaccinated localities surround the areas with a low percentage of vaccination, the virus becomes contained in low-vaccinated areas and that could result in “hyperlocal outbreaks”.


One important thing that everyone should do to make sure protection from delta variant is to get fully vaccinated. A study reported that the effectiveness of vaccine when only one dose was administered was found to be 30.7% in individuals infected with delta variant while effectiveness for one dose was 48.7% in individuals infected with the alpha variant. However, the study also reported that when two doses of the vaccines were administered, the efficacy was reported to be 88.0% for delta variant while effectiveness in individuals infected with alpha variant was observed to be 93.7%  (6).

Although there are also chances that fully vaccinated individuals with an advanced infection might infect others, the quantity of viral genetic matter in vaccinated people may reduce rapidly as reported by the CDC. Studies show that vaccinated people though carry the same quantity of virus in their mouth and noses as the unvaccinated individuals, the period for the spread of the virus from vaccinated people will be short. Keeping all this in view, the recommendations for getting a booster dose of vaccine and the eligibility criteria is also changing.

It should be kept in mind that no vaccine guarantees 100% protection from getting a coronavirus. This is why along with getting vaccinated, covering the mouth and nose with a face mask in public places where there are high chances of transmission of the virus is also recommended. Besides this, there is also a need to develop the habit of sanitizing hands frequently. Keep safe distance while in public places or much better avoid crowded places altogether. Even though one is vaccinated, the mutated variant can pass from one person to another, and taking precautions seems to be the only way to curb the spread of the virus.



  1. Vaughan A. Delta to dominate world. New Sci. 2021 Jul 3;250(3341):9.
  2. CDC. Coronavirus Disease 2019 (COVID-19) [Internet]. Centers for Disease Control and Prevention. 2020 [cited 2022 Jan 25]. Available from:
  3. Li B, Deng A, Li K, Hu Y, Li Z, Xiong Q, et al. Viral infection and transmission in a large, well-traced outbreak caused by the SARS-CoV-2 Delta variant [Internet]. medRxiv; 2021 [cited 2022 Jan 25]. p. 2021.07.07.21260122. Available from:
  4. Riley S, Wang H, Eales O, Haw D, Walters C, Ainslie K, et al. REACT-1 round 12 report: resurgence of SARS-CoV-2 infections in England associated with increased frequency of the Delta variant [Internet]. 2021 Jun [cited 2022 Jan 25]. Available from:
  5. ZOE COVID Study. What are the new top 5 COVID symptoms? [Internet]. [cited 2022 Jan 25]. Available from:
  6. Lopez Bernal J, Andrews N, Gower C, Gallagher E, Simmons R, Thelwall S, et al. Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant. N Engl J Med. 2021 Aug 12;385(7):585–94.
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