How COVID vaccines work against the Delta variant

The Delta variant of coronavirus is a source of serious concern as lab tests have shown it is more contagious and resistant to vaccines compared with other forms of COVID-19.

However, there is evidence that the available jabs retain important effectiveness against it after two doses.

Here is what you need to know:

A British study published in The Lancet medical journal in early June looked at levels of neutralising antibodies produced in vaccinated people exposed to the Delta, Alpha (first identified in Britain) and Beta (first identified in South Africa) variants.

It found that antibody levels in people with two doses of the Pfizer-BioNTech shot were six times lower in the presence of the Delta variant than in the presence of the original COVID-19 strain on which the vaccine was based.

The Alpha and Beta variants also provoked lower responses, with 2.6 times fewer antibodies for Alpha and 4.9 times fewer for Beta.

A French study from the Pasteur Institute concluded that neutralising antibodies produced by vaccination with the Pfizer-BioNTech jab are three to six times less effective against the Delta variant than against the Alpha variant.

So do vaccines still work?
Although they represent an essential marker, the levels of antibodies measured in a lab are not enough to determine the efficacy of a vaccine. In particular, they do not take into account a second immune response in the form of killer T cells – which attack already-infected cells and not the virus itself.

As a result, real-world observations are crucial to measuring vaccine effectiveness – and the first results are reassuring.

According to data published on Monday by Public Health England, vaccination with Pfizer-BioNTech and AstraZeneca jabs is as effective at preventing hospitalisation in the case of the Delta variant as it is in the case of the Alpha variant.

Two doses of the Pfizer-BioNTech jab prevent 96 percent of hospitalisations due to the Delta variant, while the AstraZeneca vaccine prevents 92 percent, according to a study involving 14,000 people. Al Jazeera