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COVID: study finds lower antibody activity against delta variant at single dose – but vaccines still work

NIAID/Wikimedia Commons, CC BY

COVID: study finds lower antibody activity against delta variant at single dose – but vaccines still work

NIAID/Wikimedia Commons, CC BY

COVID: study finds lower antibody activity against delta variant at single dose – but vaccines still work

NIAID/Wikimedia Commons, CC BY

COVID: study finds lower antibody activity against delta variant at single dose – but vaccines still work

NIAID/Wikimedia Commons, CC BY

With cases rising exponentially and restrictions lifted, it is important to understand how well the vaccines are faring against the delta variant

NIAID/Wikimedia Commons, CC BY

Zania Stamataki, University of Birmingham

Chris Whitty, the chief medical officer for England, recently announced that the delta variant is no longer of concern because it now comprises 98% of new cases in the country and is therefore “the normal variant”.

This virus has spread to at least 90 countries and is 50% more transmissible than the alpha variant (the variant first identified in Kent), which is around 50% more transmissible than the original coronavirus that caused the pandemic.

With cases rising exponentially and restrictions lifted, it is important to understand how well the vaccines are faring against the delta variant.

A new study from the Pasteur Institute in France found that the delta variant is less sensitive to neutralising antibodies (the Y-shaped proteins that latch onto the coronavirus and stop it from entering our cells). The researchers compared three “variants of concern” – alpha, beta and delta – for their sensitivity to different sets of antibodies:

  • antibodies used as drugs to treat people with COVID (monoclonals)
  • antibodies from infected people six months after they recovered
  • antibodies from vaccinated people who were previously infected
  • antibodies from vaccinated people who had not been infected.

Monoclonal antibodies are engineered by pharmaceutical companies to target a single part of the spike protein. The researchers used four of these monoclonals to test the different viruses. The alpha variant continued to be neutralised by all four monoclonals. And the delta variant was neutralised by three out of four. But the beta variant, which is known to be the most difficult to neutralise, had lost sensitivity to two out of four monoclonals.

Thankfully, our immune system makes a remarkable array of antibodies against different parts of the virus proteins. This is known as a “polyclonal response”. Do these polyclonal antibodies contain neutralising antibodies that prevent delta variant infection?

To find out, the researchers drew blood from a small group (56 people) six months after they recovered from COVID. They found a four to sixfold reduction in the neutralisation of the beta and delta variants compared with the alpha variant. This does not mean that people are more susceptible to infection with the new variants; immune protection is not merely defined by antibodies. However, it does mean that the beta and delta variants are sufficiently different from previous viruses to affect the immune response.

Encouragingly, when previously infected people were vaccinated (Pfizer, AstraZeneca or Moderna vaccines), they all showed an increase in neutralising antibodies against all three variants. A single dose of vaccine was enough to boost neutralising responses to the delta variant.

These findings chime with recent work from the University of Oxford and Public Health England (PHE), and with studies that have yet to be published.

The results were not so encouraging for those who received one dose of vaccine in the absence of a previous infection. The Oxford group reported that a single dose of vaccination conferred poor neutralising antibodies against the delta variant. This was also the case in the French study for both Pfizer and AstraZeneca vaccines at ten weeks after vaccination.

Both peer-reviewed studies showed that booster vaccinations had the desired effect of increasing neutralisation against the delta variant, albeit at lower efficacy compared with the alpha variant.

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