COVID19, Health, Stories, Vaccination

Review: What do various studies say about the ‘Delta’ Variant?


The ‘Delta’ variant which was first identified in India in October 2020 is said to be driving the recent surge in infections in multiple countries. But what do studies say about the ‘Delta Variant’? Are vaccines found to be effective against this variant? Here is a review of few studies. 

Viruses mutate constantly. The moment a virus enters its host cell or a susceptible body, it starts replicating. The coronavirus SARS-CoV-2 that is responsible for the COVID-19 pandemic is no different. It has been more than a year since the pandemic first began and hence multiple variants of SARS- CoV-2 are being detected globally. Though most mutations may be innocuous, there are some genetic changes that make the virus mutant more infectious or even help evade antibodies produced by vaccines or otherwise which can lead to further infections. 

There are four Variants of Concern (VoC) of SARS-CoV-2

Variants that show an increase in transmissibility, more infectious and causing more severe disease resulting in increased hospitalizations or deaths, reduced response to treatments and vaccines, a significant reduction in neutralization by antibodies generated during previous infection or vaccination, or failure in diagnostic detection are treated as Variants of Concern, VoC, according to the CDC. The WHO has classified four variants as VoC viz; Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), and Delta (B.1.617.2).

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Source: WHO

Delta variant is reportedly causing the recent surge in many countries 

The B.1.617.2 variant, or the Delta variant, is the latest addition to the list of VoC due to its increased transmissibility. The variant was first identified in India in October 2020. As of 07 July 2021, a total of 104 countries have reported cases of the Delta variant as per WHO’s Weekly Epidemiological Update. The recent surge in infections and hospitalizations in many of these countries has been attributed to the Delta variant, including in the UK, US, India, and Russia. Countries were forced to reimpose movement restrictions to control the spread of this variant. 

The B.1.617 lineage has three subtypes B1.617.1 (kappa), B.1.617.2 (delta), and B.1.617.3, among which B.1.617.1 and B.1.617.3 have been classified as Variants of Interest (VoI), while B.1.617.2 or the Delta variant has been classified as a Variant of Concern (VoC). The Delta Plus variant (AY.1) is the mutated version of the Delta variant (B.1.617.2) characterized by the K417N mutation in the spike protein in the virus (like in the Beta variant first identified in South Africa) which has immune evasion property. That is, it helps the virus escape the body’s immune response. 

Multiple studies are underway to study the impact & efficacy of the vaccines currently being administered around the world, against new VoCs. While most studies report reduced efficacy against the Delta variant, they conclude that the vaccines still prevent severe disease and hospitalization in those who took two doses of the vaccine. Here is a review of some of these studies. 

Unvaccinated or partially vaccinated persons are more at risk of infection from Delta variant

According to the data from Public Health England (PHE), as of 25 June 2021, the Delta variant was dominant in the UK comprising 95% of 92,029 sequenced cases. Almost 82,500 of these total cases were reported in people below 50 years of age. Majority of the cases (53,822) were reported among unvaccinated individuals, and within the cohort, 98% were in the below 50 age group and only 976 cases were among those aged above 50. With respect to mortality, a total of 117 deaths due to delta variant were reported in England with the majority in the above 50 age group. Of the eight fatalities under 50 years of age, six were unvaccinated and the remaining two had received only one dose. In other words, unvaccinated or partially vaccinated individuals are more at risk of infection.

Two doses of vaccines give high levels of effectiveness against symptomatic disease and hospitalization

PHE’s data also showed that after two doses, the Pfizer vaccine was 88% effective against the delta variant, whereas the AstraZeneca vaccine was 60% effective. Both vaccines were 33% effective against the symptomatic disease from the delta variant, three weeks after the first dose. The analysis which included 1,054 people of all age groups confirmed as having the delta variant through genomic sequencing, concluded that vaccine uptake should be maximized with both doses for vulnerable groups since high levels of vaccine effectiveness against the symptomatic disease was evident only after both doses. 

Meanwhile, another PHE analysis from June 2021 showed that the Pfizer vaccine was 96% effective against hospitalization after 2 doses while the AstraZeneca vaccine was 92% effective against hospitalization after both doses. The study was based on 14,019 symptomatic cases of which 166 were hospitalized between 12 April and 4 June 2021, at emergency hospital admissions in England.

As compared to the original virus detected in Wuhan, the effectiveness of vaccines against the VOCs is lower

A study in the UK by researchers at Imperial College London, The Francis Crick Institute, and the University of Glasgow, which is yet to be peer-reviewed, showed that the delta and beta variants are associated with lower neutralizing efficacy compared to the alpha variant or the original Wuhan strain. The study made use of the HIV (SARS-CoV-2) pseudo-virus system and found that the neutralizing efficacy was 4 to 6-fold lower against the kappa (B.1.617.1), delta, and beta variants compared to the Wuhan variant. Pfizer and AstraZeneca vaccines were used to compare the difference in the neutralization of original Wuhan lineage and the Variants of Concern- delta and beta variants, in the study. Both doses of the vaccines were more effective against the original and beta variants and, against the delta variant to a lower extent, as compared to one dose. AstraZeneca vaccine produced between 0.7 to 4-fold lower neutralizing activity against the three variants as compared to the original strain while Pfizer vaccine still showed 8 to 11-fold lower neutralizing titers (antibodies) against the three VoCs. It was also observed that Pfizer produced higher neutralizing titers than AstraZeneca. 

Covishield and Covaxin are effective against VOCs- Health Ministry

In India, Covishield, Covaxin, and Sputnik-V are the vaccines being administered for now. According to the Health Ministry’s recent press release, Covishield and Covaxin were both effective against the Variants of Concerns- Alpha, Beta, Gamma, and Delta variants. Laboratory tests to check vaccine effectiveness against Delta Plus are ongoing.

Breakthrough cases or recovered persons who received the vaccine had more protection against delta variant

An Indian study conducted by the scientists from the Indian Council of Medical Research, National Institute of Virology, Department of Neurosurgery, Command Hospital (Southern Command), and Armed Forces Medical College, Pune evaluated the immune response of five categories of people (116 participants) who received doses of Covishield-

  • those vaccinated with one dose
  • vaccinated with both doses
  • those who had recovered from COVID-19 and got vaccinated with one dose
  • those who had recovered and got vaccinated with both doses
  • Breakthrough cases (The breakthrough cases were later identified to be due to Kappa and Delta variants through genome sequencing.)

The findings suggested that breakthrough cases and those persons who received one or both vaccine doses after recovering from COVID-19 have relatively higher protection against Delta variant in comparison with those who have never been infected but got either one or two doses of the vaccine. The study called for long-term follow-up of participants to get a better understanding of infection and vaccination on long-term protection by Covishield. It also added that tracking breakthrough cases to look for unexpected changes is important to understand the impact of new variants. 

Delta variant of COVID-19 is eight times less sensitive to antibodies generated by vaccines

A recent study which is yet to be peer-reviewed, ‘SARS-CoV-2 B.1.617.2 Delta Variant Emergence and Vaccine Breakthrough: Collaborative Study, which was conducted on 100 healthcare workers Sir Ganga Ram Hospital, Indraprastha Apollo Hospital, and Northern Railway Central Hospital, revealed that the Delta variant of COVID-19 is eight times less sensitive to antibodies generated by vaccines in comparison with the original strain of the virus that was first reported in Wuhan, China. The study found that the Delta variant is less sensitive to neutralizing antibodies from recovered individuals, with higher replication efficiency as compared to the Alpha variant. The variant has high transmissibility because of the presence of enhanced spike proteins for attachment to the lung epithelial cells and so, has a higher capacity to infect people. The variant was found to dominate vaccine -breakthrough infections with higher respiratory viral loads compared to non-Delta infections. It also generated higher transmission between fully vaccinated healthcare workers, as compared to other VoCs. However, severe disease in fully vaccinated HCWs was rare. Nonetheless, the study called for extensive vaccination which will likely protect against moderate to severe disease and will reduce transmission of the Delta variant. 

Another analysis which reported 63 cases of vaccine breakthrough infections in AIIMS, Delhi also identified that majority of the breakthrough infections following vaccination with Covishield and Covaxin were caused by delta variant. The analysis also showed that irrespective of vaccine status, the viral load was high in all the patients. (Factly’s review of studies on breakthrough infections has already covered this analysis).

Continuous Monitoring & Studies are the need of the hour

To sum it up, most studies done to date conclude that vaccination offers protection to people to an extent, if not by 100%. It also helps in reducing the severity of disease or the need for hospitalization. However, to understand the infection caused by these variants and the efficacy of the vaccines against the VoCs, continuous monitoring & detailed studies must be undertaken covering different groups of the population. The genome sequencing of most samples is also necessary. Till we reach a level of herd immunity where the virus variants do not cause much damage, people are expected to follow COVID-19 appropriate behaviour even if vaccinated. Those who are not vaccinated have to take the vaccine at the earliest. 

Featured Image: COVID 19 Delta Variant


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