The Delta variant may be escaping immunity from Covid-19 vaccines

Outpacing the variant with vaccines.
Outpacing the variant with vaccines.
Image: Reuters/Adnan Abidi
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The evidence around the Delta variant is evolving, and studies now show that current vaccines may not be as effective against it.

There has been a lot of conversation around this variant’s immune escape capabilities. The terms “immune escape” or “vaccine escape” refer to a variant’s capability to infect someone who has previous immunity to Covid-19, either through past infections or vaccination.

A new study out of Cambridge University looked at the variant’s response to Covid-19 vaccines such as Astra-Zeneca (known as Covishield in India), and to the Pfizer/BioNTech shot, as well as evidence from healthcare workers infected during India’s second wave.

Is the Delta variant more resistant to AstraZeneca, Pfizer vaccines?

The analysis by the Gupta Lab at Cambridge University, a team of infectious diseases specialists led by professor of clinical microbiology Ravindra K. Gupta, found that the AstraZeneca vaccine was significantly less effective against infections from the Delta variant. This study was conducted in a lab using samples from vaccinated people and testing them against the wild type of the coronavirus (first detected in Wuhan), Alpha variants (first found in the UK), and Delta variants, first identified in India.

According to the study, which was published this week on a pre-print platform and is currently not peer-reviewed, blood from those who got the AstraZeneca vaccine was eight times less effective in blocking the Delta variant compared with the original strain. The Pfizer vaccine was also less effective against the variant, though it did produce more antibodies against the strain compared with the AstraZeneca vaccine.

Single dose and vaccine efficacy 

Data from Public Health England (PHE), the UK government’s health executive arm, have shown that single doses of the AstraZeneca and Pfizer vaccines have reduced efficacy of 33% against infections with the Delta variant, compared with over 85% against the original strain in clinical trials. For those fully vaccinated, the AstraZeneca vaccine also saw a reduction in efficacy—from 67% against the Alpha variant to 60% against Delta—but not to as alarming a degree. The PHE also found that both these vaccines were over 90% effective in reducing hospitalizations and serious disease.

Real-world data on the Delta variant cases 

The Gupta Lab’s analysis also looked at breakthrough infections—those that happen despite being fully vaccinated—among healthcare workers at three hospitals in Delhi. The city was among the worst-hit during India’s second wave between March and June, and saw new infections go as high as 28,000 per day.

The analysis found that the Delta variant was most prevalent in these hospital “infection clusters,” and while overall breakthrough rates were low, each infected person spread the infection to two or more people. While other variants prevalent in Delhi had no such infection clusters of over two people among double vaccinated healthcare workers, there were 10 of these with Delta variant infections.

“…Vaccine breakthrough clusters amongst HCW [healthcare workers] is of concern given that hospitals frequently treat individuals who may have suboptimal immune responses to vaccination due to comorbidity,” the study noted. Such patients, it said, could be at risk for severe disease after an infection from healthcare or other staff in a hospital setting. “Therefore, strategies to boost vaccine responses against variants are warranted in HCW, and attention to infection control procedures should be continued even in the post vaccine era,” it said.

This research cements the worry that Delta is fitter against the body’s immunity, making its transmission much faster than other variants. On June 25, the World Health Organization (WHO) urged vaccinated people to continue wearing masks to protect against delta variant. Experts from WHO also confirmed that the delta variant is rapidly spreading among unvaccinated people.

The ICMR’s study from Odisha

In the eastern state of Odisha, an analysis of vaccinated healthcare workers showed that of the 274 breakthrough infections reported between March 1 and June 10, 83.9% of these were symptomatic. It is not clear yet what percentage of the total vaccinated healthcare workers were represented by these 274 cases.

This study was conducted by the Regional Medical Research Centre in Bhubaneswar, which is affiliated with the Indian government’s Indian Council for Medical Research, based on voluntary reporting from healthcare workers. The ICMR’s study, too, is in the preprint stages. Of those nearly 84% were symptomatic infections, 10% needed to be hospitalized, indicating that vaccines do work, but are not 100% protective against hospitalisation. Over 87% of the 274 received the Covishield vaccine.