Immunity

Delta variant also known as B.1.617.2, which was first detected in India, has now spread through the globe and catalyzed a third wave in the UK. Observing its impact in the UK, other nations are bracing up for the variant’s impact, as this variant is a major cause of concern due to numerous reasons.

There can be some hope to dampen the inevitable rise of Delta in the nations with ample access to vaccines, but in the countries without large vaccine stocks, this variant could prove devastating.

Worldwide reports on Delta-

Although Delta has been reported in countries like Nepal, southeast Asia and elsewhere, its widespread devastation in the UK has made scientists think of ways to overcome the threat. Additionally, it is about 60% more transmissible than the already highly infectious Alpha variant (also called B.1.1.7), which raises even more concerns.

Delta may show moderate resistance to vaccines in people who have received just a single dose. A Public Health England study reported a 33% and 50% reduction in a person’s risk of developing COVID-19 symptoms by the Delta and Alpha variant respectively after a single dose of either AstraZeneca′s or Pfizer′s vaccine. While the second dose of the AstraZeneca vaccine can boost protection to 60% and 66% against Delta and Alpha respectively; and

The second dose of Pfizer’s jab can boost protection to 88% and 93% against Delta and Alpha respectively.

Delta can even increase the chances of hospitalization 2 fold than that of the alpha variant, as suggested by the Preliminary evidence from England and Scotland.

A recent Public Health England study suggests 75% less likelihood of hospitalization in people who have one vaccine dose, compared with unvaccinated individuals, and 94% less likelihood of hospitalization in those who are fully protected by 2 doses of vaccination.

Indian Scenario-

The data from India suggest that it became the dominant variant due to the following reasons-

1. Its improved ability to jump to new hosts  
2. Its ability to wipe resistance of population immunity in people from the first wave of Covid-19
3. It has the maximum transmissibility yet seen
4. Presence of a unique set of mutations making the virus more infective, leading to a higher viral load in people and causing larger outbreak clusters.

An astonishing report on Delta from India-

Indian researchers including scientists from the Institute of Genomics and Integrative Biology (IGIB) in collaboration with Cambridge University’s Gupta Lab have investigated-

1. Outbreak patterns among healthcare workers in three Indian cities
2. Lab analysis of how the variant reacts to antibodies?
3. How the virus infects human cells, particularly in the lungs?

They found the Delta variant to have a good immune escape potential. It was also found to quickly replace other variants and cause most of the breakthrough infections (infection after complete vaccination) in healthcare workers. 

In Mumbai, the Delta variant was found to be 10%-40% more transmissible than previously circulating lineages, and was able to evade 20-55% of the immune protection provided by prior infection with a non-Delta virus.

The in-vitro, or laboratory studies, investigating the sensitivity of the variants in neutralizing antibodies showed that the Alpha variant was 2.3 fold less sensitive and, Beta was 8.2 fold less sensitive as compared to 5.7 fold for the Delta variant.

Delta variant was also found to have a replication advantage over Alpha variant in the lab.

Thus it advised people to be very cautious and follow COVID appropriate norms. The researchers are further investigating its immune escape potential. 

The ICMR’s study from Odisha (India)-

A study conducted by the Regional Medical Research Centre in Bhubaneswar analyzed vaccinated healthcare workers and reported 274 breakthrough infections between March and June 2021, 83.9% of which were symptomatic. Of these 83.9% symptomatic infections, 10% needed hospitalization, indicating that vaccines do work, but are not 100% protective against hospitalization. More than 87% of 274 healthcare workers received the Covishield vaccine.

Effect of vaccination on Delta-

Delta variant, with limited data and studies, is still the topic to explore and learn. Certain studies have reported the in-effectiveness of current vaccines against this variant. Delta variant’s immune escape capabilities are still the topic of debate. “Immune escape” or “vaccine escape” are terms to represent a variant’s capability to infect someone who has previous immunity to Covid-19, either through past infections or vaccination.

Delta variant′s resistance to AstraZeneca, Pfizer vaccines explained-

The analysis by the Gupta Lab at Cambridge University found that the AstraZeneca vaccine was significantly less effective against infections from the Delta variant. Blood samples from those who got the AstraZeneca vaccine proved eight times less effective in blocking the Delta variant compared with the original strain, in vitro. The Pfizer vaccine was also found to be less effective against the variant but produced more antibodies against the strain compared to that of the AstraZeneca vaccine.

World Health Organization (WHO)’s say on Delta-

WHO has confirmed that the delta variant is rapidly spreading among unvaccinated people and has urged vaccinated people to continue wearing masks to protect against delta variants.