Scientists are studying how well COVID-19 vaccines work against the delta variant of SARS-CoV-2. We discuss the latest findings.

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How much protection against the delta variant of SARS-CoV-2 can vaccines provide? Bloomberg Creative/Getty Images

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The delta variant of SARS-CoV-2, which was first identified in India, is now the dominant form of the virus in the United Kingdom. In the United States, at least 10% of new cases are with this variant.

Data from the U.K. show that new SARS-CoV-2 infections have increased by 31% in the past 7 days. Moreover, an analysis from Public Health England (PHE) suggests that the delta variant is more transmissible than previous ones and that it is more likely to lead to treatment in the hospital.

Yet recent data indicate that vaccines are effective at preventing severe COVID-19 caused by the delta variant that would require hospital treatment.

In this article, we present up-to-date research on how well COVID-19 vaccines work against the delta variant.

Article highlights:

A recent analysis from PHE looks at how likely people who had an infection with the delta variant were to need treatment in the hospital.

The report puts the protection from requiring hospital treatment for COVID-19 at 71% after one dose and at 92% after two doses of the Oxford-AstraZeneca vaccine. The Pfizer vaccine was 94% effective at preventing hospitalization after the first dose and 96% after two doses.

In India, the Oxford-AstraZeneca COVID-19 vaccine bears the name Covishield.

The report, which has not been peer-reviewed yet, puts these percentages on a par with protection against the alpha variant, or B.1.1.7, which scientists first identified in the U.K.

“These findings indicate very high levels of protection against hospitalization with the delta variant with one or two doses of either vaccine,” the authors write.

It comes after an earlier report that indicates COVID-19 vaccines were less effective at protecting people from COVID-19 if they had only received the first dose of the Pfizer-BioNTech or Oxford-AstraZeneca vaccines.

However, in the analysis, which has not yet undergone peer review, the researchers measured any symptomatic case of COVID-19, regardless of severity.

In a new study, not yet peer-reviewed, scientists from Moderna found that antibodies from vaccinated clinical trial volunteers could effectively neutralize a model virus that carries the SARS-CoV-2 spike protein with the delta variant mutations.

The team investigated how well serum from eight trial volunteers who received the Moderna COVID-19 vaccine could neutralize the model virus, or pseudovirus.

The researchers made a number of these pseudoviruses to represent the delta variant and other variants of concern, including the alpha variant, first identified in the United Kingdom, and the beta variant, first identified in South Africa.

While the ability to neutralize the delta variant was lower compared with the alpha variant and the previously dominant variant, the study authors say all of the variants “remained susceptible” to neutralization by antibodies generated in response to the Moderna vaccine.

There is next to no data on how other COVID-19 vaccines are faring against the delta variant at this stage.

A small research study, not yet peer-reviewed, from scientists at the Indian Council of Medical Research and Bharat Biotech International, who co-developed the Covaxin COVID-19 vaccine, reports on its effectiveness against the delta variant.

The researchers found that antibodies from vaccinated individuals were not as effective at neutralizing the virus variant in a lab study. Despite this, they write that the vaccine’s “neutralization potential is well established.” They attribute this to the way the vaccine works.

Covaxin is made from the entire SARS-CoV-2 virus, chemically altered to prevent it from replicating.

When a person receives the vaccine, they can make antibodies to many different parts of the virus. If one part mutates to give rise to a new variant, such as the delta variant, then antibodies to other parts of the virus should still confer enough protection.

However, the study was small, and further research is necessary to look at how effective the Covaxin COVID-19 vaccine is in real-life settings at preventing severe COVID-19 from the delta variant.

The makers of the Russian Sputnik V COVID-19 vaccine recently announced on Twitter that their vaccine was more effective against the delta variant than others. They added that they had submitted the data to an international peer-reviewed journal.

The company also said that it would soon be offering a booster shot specifically designed to work against the delta variant.

Until such time as the data are publicly available, it is not possible to assess the validity of these statements about the Sputnik V vaccine.

There is also little data available about how effective the Sinovac COVID-19 vaccine (CoronaVac) is against the delta variant. A recent Reuters news piece reports that over 350 doctors and medical staff in Indonesia developed COVID-19 despite receiving CoronaVac.

According to the report, “Most of the workers were asymptomatic and self-isolating at home, said Badai Ismoyo, head of the health office in the district of Kudus in central Java, but dozens were in hospital with high fevers and falling oxygen saturation levels.”

The region is seeing high numbers of infections, which experts believe are mostly due to the delta variant. Given the Reuters report, it is clear that more research is needed to establish exactly how well CoronaVac can protect from severe COVID-19 due to the delta variant.

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