The past two months have witnessed a consistent decline in the spread of Covid-19 in India. The number of new cases reported daily and active caseload have fallen steadily. The vaccination drive has picked up pace across the country and restrictions on economic activity have been withdrawn fully. While this scenario may make one believe that the worst of Covid-19 is over in the country, the truth could well be far from it. 

Fuelled by newer, immunity evading variants, easing of mandates on Covid appropriate behaviour, “pandemic fatigue” causing people to socialize despite the perceived risk, and travel relaxations, the Covid-19 pandemic continues to resurface and rage in many parts of the world. With over 40,000 new cases being reported in India every day and only five percent of its population fully vaccinated[1], India’s fight against Covid-19 has quite some distance to cover. The fact that the virus is still actively circulating in the country increases the possibility of future waves, which some experts believe are in fact inevitable. A recent research report has warned that a third wave could hit India as early as September[2].

Given the highly infectious nature of the Delta variant and its more recently discovered sub-lineage Delta Plus, it is imperative that governments, health systems, and people do not repeat the mistakes made at the time of the receding first wave. Today, the Delta variant that drove the devastating second wave in India, has become the dominant virus strain not just in India but also in the United Kingdom[3]. South Africa is currently witnessing a massive surge of infections attributed to the Delta variant[4]. Delta is likely to become the dominant virus in the United States in the coming weeks. 

In a recent public statement, the WHO said that the Delta variant has been detected in at least 98 countries with scenes of hospitals overflowing and fresh lockdowns becoming the norm yet again in many countries, especially those with low vaccination coverage[5]. Calling it a “dangerous period” for the world, WHO warned that the Delta variant is transmitting rapidly and is continuing to evolve and mutate. Adding to global concerns, a new variant termed “Lambda” that originated in Peru is now spreading rapidly in South America. As variants continue to pose new challenges, the global health agency has advised governments for constant evaluation and careful adjustment of their public health response.

Why should we be wary of the Delta variant? 

The Delta variant (B.1.617.2) was the fourth mutant strain to be recognized as a ‘variant of concern’ following UK’s Alpha  (B.1.1.7), South Africa’s Beta (B.1.351) and Brazil’s Gamma (P.1) variants. Research suggests that Delta is the most contagious of all the known variants to date[6].  The first sample of the Delta variant was isolated in India in December last year. The strain largely drove the second wave of Covid cases in India, accounting for as much as 75 per cent of genome sequences from the country[7].  As per more recent data, 90 percent of samples tested in India have been found to have the Delta variant[8].

A way for epidemiologists to determine the transmissibility of a new variant is to examine how many more persons can an infected person infect and how easily or rapidly. This involves tracking the close contacts of people who have been infected and seeing how many others tested positive. Delta is believed to be spreading 50 percent faster than Alpha, which was 50 percent more contagious than the original strain of Covid-19, making the new variant 75 percent more contagious than the original[9]. The high transmissibility of Delta was recently proven by research conducted by health officials in Australia where, based on the analysis of CCTV footage of an indoor shopping mall, it was found that fleeting encounters of five to 10 seconds between people walking past each other were enough for the virus to transmit from one person to another. Less than 10 percent of Australia’s population is fully vaccinated.

While the Delta variant is proven to be more infectious than the Alpha strain, more research is needed on how much more fatal it is, even as there are indications that it may cause more severe disease. A study published in the journal The Lancet examined the impact of the delta variant in Scotland, where it had become the dominant strain. It found that the risk of hospitalization from Covid-19 was roughly doubled for patients infected with delta, compared with people infected with the alpha variant[10].

Delta poses the biggest risk to countries that have limited access to vaccines, particularly those in Asia and Africa, where most nations have vaccinated less than 5 percent of their populations. In general, it has been found in a recent study[11] that children and young people (under 50) were more likely to become infected with the delta variant. As older age groups get vaccinated, those who are younger and unvaccinated will be at higher risk of getting Covid-19 with any variant, the study says.

Are vaccines effective against the Delta variant?

Amidst the rapid spread of the Delta variant, research based on the limited data coming from vaccinated population indicates that the vaccines currently in use are preventing severe illness, hospitalisations and causing fewer deaths as compared to unvaccinated people. The vaccines appear to offer good protection against the delta variant, and most experts agree that fully vaccinated individuals likely face little risk. 

Although vaccines have been shown to work against Delta, several studies have reported that the variant could impede the ability of vaccine-induced antibodies to fight the virus. These studies have found delta to be moderately resistant to vaccines, particularly in people who have received just a single dose. Though there isn’t much need for worry among people who are fully vaccinated, public health officials are concerned about outbreaks in places with low vaccination rates.

A recent study by researchers of the Indian SARS-CoV-2 Genomics Consortium (INSACOG), suggests that breakthrough infections — infections in people who have been vaccinated — are disproportionately high due to the Delta variant[12]. The study, which is yet to be peer reviewed,  suggests that this variant likely has the ability to evade the immune system of the body.

A study by Public Health England[13] published in May found that a single dose of either AstraZeneca’s or Pfizer’s vaccine reduced a person’s risk of developing COVID-19 symptoms caused by the Delta variant by 33 percent, compared to 50 percent for the Alpha variant. A second dose of the AstraZeneca vaccine boosted protection against Delta to 60 percent (compared to 66 percent against Alpha), while two doses of Pfizer’s jab were 88 percent effective (compared to 93 percent against Alpha)[14].

Another study by The Lancet[15] suggests that there is a mixed picture on single-dose efficacy of currently available vaccines against delta.  Early findings from the UK suggest that single-dose efficacy of the Astra Zeneca vaccine against this variant is substantially reduced when considering symptomatic infection. However, more recent findings suggest that protection against hospitalisation is as high as 71 percent. 

A study conducted by the Christian Medical College (CMC) in Vellore found that vaccines are highly effective in preventing symptomatic infections and hospitalisation among healthcare workers who are at a higher risk of being infected. The study, presented through a preprint paper[16] found that one dose of vaccine offered 61 percent protective effect against infection, while two doses offered 65 percent. Significantly, one dose reduced the risk of hospitalisation by 70 percent and two doses by 77 percent.

According to a recent study by the Indian Council of Medical Research, Covid recovered persons with even one dose of the Covishield vaccine have higher protection against the Delta variant than those who have never been infected but have got vaccinated[17]. The study also found that neutralising antibodies against the delta variant were not found in 16.1 per cent samples from those who had been administered both doses of the Covishield vaccine. Further, neutralising antibodies were not observed in 58.1 per cent of serum samples from those who had been given only one shot of Covishield.

As far as the Johnson and Johnson jab is concerned, the US pharma company recently said that its vaccine works against the delta variant and other highly prevalent viral variants of the virus that causes COVID-19. J&J said it had submitted the data to the website bioRxiv ahead of peer review[18].

What is the “delta plus” variant?

Adding to challenges posed by the spread of the Delta variant, a new mutated strain dubbed the “Delta Plus” has slowly started to surface in the country.  The new mutation in the Delta variant was first detected in Europe in March. In June, Covid patients in India were also found to have the mutant virus.  The Delta Plus variant was announced by the Ministry of Health and Family Welfare in late June. It has been labelled by the ministry as a variant of concern[19]. The ministry classifies a variant as one of concern as soon as there’s evidence for increased transmission, as may be the case with the latest variant[20].

By June 24, only about 40 cases of Delta Plus infections were reported by Indian health officials, based on genetic sequencing of the virus from positive patients. But given the original Delta strain’s ability to transmit more efficiently from person to person, and to potentially cause more severe disease, health authorities raising concern is the prudent thing to do. Delta plus has not yet been designated a variant of concern by the WHO or the CDC. Even though cases involving delta plus have been reported in 11 countries, including the U.S, it is not yet clear if delta plus carries additional risks or is associated with increased transmissibility.

According to the Indian health ministry, like the original Delta variant, the Delta plus could have the ability to evade immunity[21]. The ministry said in a statement that the Delta Plus variant has been classified as a variant of concern because of increased transmissibility, stronger binding to receptors of lung cells, potential reduction in monoclonal antibody response and potential post vaccination immune escape. The ministry has alerted states where the said variant has been found. Maharashtra, Kerala and Madhya Pradesh have been advised that the public health response measures, while broadly remaining the same, have to be more focused and effective. 

The Delta plus variant might have a similar degree of reduction in efficacy against the vaccines currently in use as its original delta strain. It is therefore feared that the mutation may fuel another wave of infections in the country.  Studies are under way to assess the effectiveness of vaccines against Delta plus[22]

Vaccination Coverage in India 

Following the shift in the national Covid-19 vaccination policy, announced in early June, the pace of vaccine coverage has gained some momentum in the country. The Centre has reversed its April policy of decentralized vaccine purchases to make the process centralized again wherein the procurement and distribution of vaccines will be carried out by the Union Government.  As per the new policy,  that came into effect on June 21 the Union Government would acquire 75 percent of all vaccine stock of the country and distribute it free of cost to the states. These jabs will be administered free of cost to all citizens.  Private hospitals will be at liberty to buy a quarter of the national output, but can charge a service fee no higher than ₹150 to administer such privately-procured jabs.

As of July 4, 6.4 crore Indians have been fully vaccinated while 28.71 crore Indians have received a single dose of the vaccine. Despite the recent increase in the pace of vaccination, there is still a long way to go before a considerable percentage of the population is vaccinated for the pandemic to be truly brought under control. 

The ramp up of vaccination is likely to be sustained and also improved in view of additional vaccines that are likely to be made available soon. Russian vaccine Sputnik V is likely to see a full launch across the country in the coming weeks. Currently, it is being administered in a few private hospitals as a part of its pilot launch that started on May 14. 

With Moderna’s first batch expected in India soon, the vaccine by the American drug maker will likely become the fourth vaccine to be available for use in India. The vaccine doses will be imported by Indian drug manufacturer Cipla. The Centre plans to provide the Moderna doses directly to states. India is receiving the Moderna vaccine doses under the COVAX scheme of the WHO, a few days after the DGCI granted approval to it. Last month, Pfizer said that the company is in the final stages of getting approval for its Covid-19 vaccine from the Indian government. When approved, the pharma giant is expected to supply one billion doses to India within this year. 

The Indian government is also in talks with Johnson & Johnson regarding its single-shot vaccine, which the company claims shows promising signs of protection against the Delta variant As per the government’s plan, the J&J vaccine will be produced by Hyderabad based pharma company Biological E. The other foreign developed vaccine that will be made available in India soon is that of American biotechnology company Novavax. The government gave Serum Institute of India (SII) the go-ahead to manufacture and stockpile the vaccine. The clinical trials are underway in India and the vaccine is likely to hit the market under the name Covovax by September this year.

The road ahead

With over 40,000 cases being reported from the country every day and strong indications of a likely third wave, the fight against Covid-19 must continue with the same intensity. Preparation for, and response to, a third wave will require a concerted nationwide effort with proper coordination between the centre and states. Healthcare establishments will need to plan for resources assuming worst case scenarios so as to avert the unmanageable burden brought on it by the second wave that cracked the Indian healthcare system. 

In addition to the response of the health system, if people continue to follow all Covid appropriate behaviour diligently, at least till a significant proportion of the population is vaccinated, we will be able to greatly diffuse the intensity of future waves. 

Increasing vaccination rates therefor remains a high priority. Vaccines confer stronger and longer immunity than natural infection. If we achieve 60 percent coverage, the rates of infection and deaths will come down sharply. Furthermore, vaccination strategies need to evolve as new variants of the virus variants emerge. Governments need to take proactive measures to improve vaccines uptake among vulnerable groups through intense community engagement and communication campaigns. Community-based outreach will help speed up the vaccination programme and address the issue of vaccine hesitancy. Adaptive vaccination strategies can play a vital role in protecting lives as the Covid-19 pandemic is continuing to unfold.

The past two months have witnessed a consistent decline in the spread of Covid-19 in India. The number of new cases reported daily and active caseload have fallen steadily. The vaccination drive has picked up pace across the country and restrictions on economic activity have been withdrawn fully. While this scenario may make one believe that the worst of Covid-19 is over in the country, the truth could well be far from it. 

Fuelled by newer, immunity evading variants, easing of mandates on Covid appropriate behaviour, “pandemic fatigue” causing people to socialize despite the perceived risk, and travel relaxations, the Covid-19 pandemic continues to resurface and rage in many parts of the world. With over 40,000 new cases being reported in India every day and only five percent of its population fully vaccinated, India’s fight against Covid-19 has quite some distance to cover. The fact that the virus is still actively circulating in the country increases the possibility of future waves, which some experts believe are in fact inevitable. A recent research report has warned that a third wave could hit India as early as September.

Given the highly infectious nature of the Delta variant and its more recently discovered sub-lineage Delta Plus, it is imperative that governments, health systems, and people do not repeat the mistakes made at the time of the receding first wave. Today, the Delta variant that drove the devastating second wave in India, has become the dominant virus strain not just in India but also in the United Kingdom. South Africa is currently witnessing a massive surge of infections attributed to the Delta variant. Delta is likely to become the dominant virus in the United States in the coming weeks. 

In a recent public statement, the WHO said that the Delta variant has been detected in at least 98 countries with scenes of hospitals overflowing and fresh lockdowns becoming the norm yet again in many countries, especially those with low vaccination coverage. Calling it a “dangerous period” for the world, WHO warned that the Delta variant is transmitting rapidly and is continuing to evolve and mutate. Adding to global concerns, a new variant termed “Lambda” that originated in Peru is now spreading rapidly in South America. As variants continue to pose new challenges, the global health agency has advised governments for constant evaluation and careful adjustment of their public health response.

Why should we be wary of the Delta variant? 

The Delta variant (B.1.617.2) was the fourth mutant strain to be recognized as a ‘variant of concern’ following UK’s Alpha  (B.1.1.7), South Africa’s Beta (B.1.351) and Brazil’s Gamma (P.1) variants. Research suggests that Delta is the most contagious of all the known variants to date.  The first sample of the Delta variant was isolated in India in December last year. The strain largely drove the second wave of Covid cases in India, accounting for as much as 75 per cent of genome sequences from the country.  As per more recent data, 90 percent of samples tested in India have been found to have the Delta variant.

A way for epidemiologists to determine the transmissibility of a new variant is to examine how many more persons can an infected person infect and how easily or rapidly. This involves tracking the close contacts of people who have been infected and seeing how many others tested positive. Delta is believed to be spreading 50 percent faster than Alpha, which was 50 percent more contagious than the original strain of Covid-19, making the new variant 75 percent more contagious than the original. The high transmissibility of Delta was recently proven by research conducted by health officials in Australia where, based on the analysis of CCTV footage of an indoor shopping mall, it was found that fleeting encounters of five to 10 seconds between people walking past each other were enough for the virus to transmit from one person to another. Less than 10 percent of Australia’s population is fully vaccinated.

While the Delta variant is proven to be more infectious than the Alpha strain, more research is needed on how much more fatal it is, even as there are indications that it may cause more severe disease. A study published in the journal The Lancet examined the impact of the delta variant in Scotland, where it had become the dominant strain. It found that the risk of hospitalization from Covid-19 was roughly doubled for patients infected with delta, compared with people infected with the alpha variant.

Delta poses the biggest risk to countries that have limited access to vaccines, particularly those in Asia and Africa, where most nations have vaccinated less than 5 percent of their populations. In general, it has been found in a recent study that children and young people (under 50) were more likely to become infected with the delta variant. As older age groups get vaccinated, those who are younger and unvaccinated will be at higher risk of getting Covid-19 with any variant, the study says.

Are vaccines effective against the Delta variant?

Amidst the rapid spread of the Delta variant, research based on the limited data coming from vaccinated population indicates that the vaccines currently in use are preventing severe illness, hospitalisations and causing fewer deaths as compared to unvaccinated people. The vaccines appear to offer good protection against the delta variant, and most experts agree that fully vaccinated individuals likely face little risk. 

Although vaccines have been shown to work against Delta, several studies have reported that the variant could impede the ability of vaccine-induced antibodies to fight the virus. These studies have found delta to be moderately resistant to vaccines, particularly in people who have received just a single dose. Though there isn’t much need for worry among people who are fully vaccinated, public health officials are concerned about outbreaks in places with low vaccination rates.

A recent study by researchers of the Indian SARS-CoV-2 Genomics Consortium (INSACOG), suggests that breakthrough infections — infections in people who have been vaccinated — are disproportionately high due to the Delta variant. The study, which is yet to be peer reviewed,  suggests that this variant likely has the ability to evade the immune system of the body.

A study by Public Health England published in May found that a single dose of either AstraZeneca’s or Pfizer’s vaccine reduced a person’s risk of developing COVID-19 symptoms caused by the Delta variant by 33 percent, compared to 50 percent for the Alpha variant. A second dose of the AstraZeneca vaccine boosted protection against Delta to 60 percent (compared to 66 percent against Alpha), while two doses of Pfizer’s jab were 88 percent effective (compared to 93 percent against Alpha).

Another study by The Lancet suggests that there is a mixed picture on single-dose efficacy of currently available vaccines against delta.  Early findings from the UK suggest that single-dose efficacy of the Astra Zeneca vaccine against this variant is substantially reduced when considering symptomatic infection. However, more recent findings suggest that protection against hospitalisation is as high as 71 percent. 

A study conducted by the Christian Medical College (CMC) in Vellore found that vaccines are highly effective in preventing symptomatic infections and hospitalisation among healthcare workers who are at a higher risk of being infected. The study, presented through a preprint paper found that one dose of vaccine offered 61 percent protective effect against infection, while two doses offered 65 percent. Significantly, one dose reduced the risk of hospitalisation by 70 percent and two doses by 77 percent.

According to a recent study by the Indian Council of Medical Research, Covid recovered persons with even one dose of the Covishield vaccine have higher protection against the Delta variant than those who have never been infected but have got vaccinated. The study also found that neutralising antibodies against the delta variant were not found in 16.1 per cent samples from those who had been administered both doses of the Covishield vaccine. Further, neutralising antibodies were not observed in 58.1 per cent of serum samples from those who had been given only one shot of Covishield.

As far as the Johnson and Johnson jab is concerned, the US pharma company recently said that its vaccine works against the delta variant and other highly prevalent viral variants of the virus that causes COVID-19. J&J said it had submitted the data to the website bioRxiv ahead of peer review.

What is the “delta plus” variant?

Adding to challenges posed by the spread of the Delta variant, a new mutated strain dubbed the “Delta Plus” has slowly started to surface in the country.  The new mutation in the Delta variant was first detected in Europe in March. In June, Covid patients in India were also found to have the mutant virus.  The Delta Plus variant was announced by the Ministry of Health and Family Welfare in late June. It has been labelled by the ministry as a variant of concern. The ministry classifies a variant as one of concern as soon as there’s evidence for increased transmission, as may be the case with the latest variant.

By June 24, only about 40 cases of Delta Plus infections were reported by Indian health officials, based on genetic sequencing of the virus from positive patients. But given the original Delta strain’s ability to transmit more efficiently from person to person, and to potentially cause more severe disease, health authorities raising concern is the prudent thing to do. Delta plus has not yet been designated a variant of concern by the WHO or the CDC. Even though cases involving delta plus have been reported in 11 countries, including the U.S, it is not yet clear if delta plus carries additional risks or is associated with increased transmissibility.

According to the Indian health ministry, like the original Delta variant, the Delta plus could have the ability to evade immunity. The ministry said in a statement that the Delta Plus variant has been classified as a variant of concern because of increased transmissibility, stronger binding to receptors of lung cells, potential reduction in monoclonal antibody response and potential post vaccination immune escape. The ministry has alerted states where the said variant has been found. Maharashtra, Kerala and Madhya Pradesh have been advised that the public health response measures, while broadly remaining the same, have to be more focused and effective. 

The Delta plus variant might have a similar degree of reduction in efficacy against the vaccines currently in use as its original delta strain. It is therefore feared that the mutation may fuel another wave of infections in the country.  Studies are under way to assess the effectiveness of vaccines against Delta plus. 

Vaccination Coverage in India 

Following the shift in the national Covid-19 vaccination policy, announced in early June, the pace of vaccine coverage has gained some momentum in the country. The Centre has reversed its April policy of decentralized vaccine purchases to make the process centralized again wherein the procurement and distribution of vaccines will be carried out by the Union Government.  As per the new policy,  that came into effect on June 21 the Union Government would acquire 75 percent of all vaccine stock of the country and distribute it free of cost to the states. These jabs will be administered free of cost to all citizens.  Private hospitals will be at liberty to buy a quarter of the national output, but can charge a service fee no higher than ₹150 to administer such privately-procured jabs.

As of July 4, 6.4 crore Indians have been fully vaccinated while 28.71 crore Indians have received a single dose of the vaccine. Despite the recent increase in the pace of vaccination, there is still a long way to go before a considerable percentage of the population is vaccinated for the pandemic to be truly brought under control. 

The ramp up of vaccination is likely to be sustained and also improved in view of additional vaccines that are likely to be made available soon. Russian vaccine Sputnik V is likely to see a full launch across the country in the coming weeks. Currently, it is being administered in a few private hospitals as a part of its pilot launch that started on May 14. 

With Moderna’s first batch expected in India soon, the vaccine by the American drug maker will likely become the fourth vaccine to be available for use in India. The vaccine doses will be imported by Indian drug manufacturer Cipla. The Centre plans to provide the Moderna doses directly to states. India is receiving the Moderna vaccine doses under the COVAX scheme of the WHO, a few days after the DGCI granted approval to it. Last month, Pfizer said that the company is in the final stages of getting approval for its Covid-19 vaccine from the Indian government. When approved, the pharma giant is expected to supply one billion doses to India within this year. 

The Indian government is also in talks with Johnson & Johnson regarding its single-shot vaccine, which the company claims shows promising signs of protection against the Delta variant As per the government’s plan, the J&J vaccine will be produced by Hyderabad based pharma company Biological E. The other foreign developed vaccine that will be made available in India soon is that of American biotechnology company Novavax. The government gave Serum Institute of India (SII) the go-ahead to manufacture and stockpile the vaccine. The clinical trials are underway in India and the vaccine is likely to hit the market under the name Covovax by September this year.

The road ahead

With over 40,000 cases being reported from the country every day and strong indications of a likely third wave, the fight against Covid-19 must continue with the same intensity. Preparation for, and response to, a third wave will require a concerted nationwide effort with proper coordination between the centre and states. Healthcare establishments will need to plan for resources assuming worst case scenarios so as to avert the unmanageable burden brought on it by the second wave that cracked the Indian healthcare system. 

In addition to the response of the health system, if people continue to follow all Covid appropriate behaviour diligently, at least till a significant proportion of the population is vaccinated, we will be able to greatly diffuse the intensity of future waves. 

Increasing vaccination rates therefore remains a high priority. Vaccines confer stronger and longer immunity than natural infection. If we achieve 60 percent coverage, the rates of infection and deaths will come down sharply. Furthermore, vaccination strategies need to evolve as new variants of the virus variants emerge. Governments need to take proactive measures to improve vaccines uptake among vulnerable groups through intense community engagement and communication campaigns. Community-based outreach will help speed up the vaccination programme and address the issue of vaccine hesitancy. Adaptive vaccination strategies can play a vital role in protecting lives as the Covid-19 pandemic is continuing to unfold.

References:

[1]https://www.pib.gov.in/PressReleasePage.aspx?PRID=1732583

[2] https://scroll.in/latest/999392/third-wave-of-covid-can-hit-india-in-august-may-reach-peak-in-september-says-sbi-report

[3]https://www.bmj.com/content/373/bmj.n1445

[4] https://www.theguardian.com/world/2021/jul/04/health-service-buckling-as-third-coronavirus-wave-fuelled-by-delta-variant-sweeps-across-south-africa

[5] https://indianexpress.com/article/india/delta-variant-is-dangerous-continues-to-evolve-and-mutate-who-chief-7387142/

[6] https://www.nbcnews.com/science/science-news/delta-delta-variants-everything-need-know-rcna1281

[7]https://theprint.in/health/covid-variant-b-1-617-2-is-spreading-fast-in-india-genome-data-shows/656375/

[8] https://pib.gov.in/PressReleasePage.aspx?PRID=1730875

[9] https://www.yalemedicine.org/news/5-things-to-know-delta-variant-covid

[10] https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01358-1/fulltext

[11] https://spiral.imperial.ac.uk/handle/10044/1/89629

[12] https://www.medrxiv.org/content/10.1101/2021.06.02.21258076v1

[13] https://www.gov.uk/government/news/vaccines-highly-effective-against-b-1-617-2-variant-after-2-dose

[14] https://www.nature.com/articles/d41586-021-01696-3

[15] https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)01290-3/fulltext#coronavirus-linkback-header

[16]https://els-jbs-prod-cdn.jbs.elsevierhealth.com/pb/assets/raw/Health%20Advance/journals/jmcp/jmcp_ft96_6_2.pdf

[17]https://www.biorxiv.org/content/10.1101/2021.07.01.450676v1

[18]https://www.biorxiv.org/content/10.1101/2021.07.01.450707v1

[19] https://www.pib.gov.in/PressReleasePage.aspx?PRID=1729467

[20] https://pib.gov.in/PressReleasePage.aspx?PRID=1730875

[21]https://pib.gov.in/PressReleaseIframePage.aspx?PRID=1730875

[22]https://www.livemint.com/news/india/india-to-study-effectiveness-of-vaccines-on-delta-plus-variant-of-sars-cov2-11624630994005.html

Additional  References:

https://www.thelancet.com/journals/langlo/article/PIIS2214-109X(21)00284-9/fulltext

https://www.biorxiv.org/content/10.1101/2021.07.01.450676v1

https://www.wsj.com/articles/delta-variants-spread-hobbles-global-efforts-to-lift-covid-19-restrictions-11625131968

https://www.yalemedicine.org/news/5-things-to-know-delta-variant-covid