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Senin, 08 Februari 2021

“Reality check”: In early data, AstraZeneca vaccine offers minimal protection against South African variant - Sydney Morning Herald

Australian health authorities have backed AstraZeneca’s vaccine despite a decision by South African authorities to delay rolling out the jab after early clinical data showed it offered minimal protection against the COVID-19 variant spreading through that country.

Health Minister Greg Hunt on Monday confirmed AstraZeneca’s vaccine would start arriving in Australia in early March.

Health Minister Greg Hunt and Prime Minister Scott Morrison.

Health Minister Greg Hunt and Prime Minister Scott Morrison.Credit:Alex Ellinghausen

“The advice I received both from the Chief Medical Officer in writing and in discussion with the head of the vaccine’s taskforce Professor Brendan Murphy this morning is preliminary, but there is currently no evidence to indicate a reduction in the effectiveness of the AstraZeneca or Pfizer vaccines in preventing severe disease or death,” Mr Hunt said.

On Monday morning South African authorities said they would suspend use of the AstraZeneca shot after clinical data showed it gave minimal protection against B.1.351, a variant of SARS-CoV-2 which contains several mutations that cut the ability of antibodies to neutralise the virus.

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It remains unclear if the vaccine will still protect against serious illness and death; scientists who were part of the South African trial are hopeful it will.

The University of Oxford, which co-developed the vaccine, said it was working on a booster jab to provide protection against the variant, if necessary.

CSL, which is contracted by the government and AstraZeneca to produce 50 million doses of the vaccine at its Broadmeadows plant, did not comment directly on whether it could modify the jab or produce a booster.

Early results from a small study of AstraZeneca’s vaccine against the South African variant, which have not yet been published or peer reviewed, suggested the vaccine reduced the chances of catching B.1.351 by only 10 per cent. However, the study was so small the results are not statistically significant.

“Until the end of October, the AstraZeneca vaccine was showing tremendous potential,” Professor Shabir Madhi, who led the trial, said at a news conference organised by the South African National Department of Health.

But after October, as the variant spread through the country, the efficacy of AstraZeneca’s vaccine collapsed, the study showed.

“These results are a reality check. It is time for us, unfortunately, to recalibrate our expectations of COVID-19 vaccines,” said Professor Madhi, who is professor of vaccinology at the University of the Witwatersrand in Johannesburg.

The small trial did not generate enough data to show if the vaccine protected against severe illness or death, as opposed to catching the virus. “I believe that might still be biologically plausible,” said Professor Madhi.

Vaccines induce protection by stimulating the production of antibodies and T cells, immune cells that hunt and kill infected cells.

In animals, T cells seem particularly important for protecting against severe disease and death.

This 2020 electron microscope image provided by the National Institute of Allergy and Infectious Diseases - Rocky Mountain Laboratories shows SARS-CoV-2 virus particles which causes COVID-19, isolated from a patient in the U.S., emerging from the surface of cells cultured in a lab.

This 2020 electron microscope image provided by the National Institute of Allergy and Infectious Diseases - Rocky Mountain Laboratories shows SARS-CoV-2 virus particles which causes COVID-19, isolated from a patient in the U.S., emerging from the surface of cells cultured in a lab.Credit:AP

Importantly, laboratory data suggests T cells are able to detect the variant, even if it can escape antibodies.

In the lab, AstraZeneca’s vaccine seems to induce similar T cell responses to Johnson & Johnson’s vaccine – which provided 85 per cent protection against serious illness when tested against the variant.

“We believe those T-cell responses will still remain intact,” said Professor Madhi.

Professor Trevor Drew, director of the CSIRO’s Australian Centre for Disease Preparedness, led studies which investigated how AstraZeneca’s vaccine worked in ferrets and showed the virus still replicating in the nose even in vaccinated animals.

Morocco’s King Mohammed VI receives the COVID-19 vaccine at the Royal Palace in Fez.

Morocco’s King Mohammed VI receives the COVID-19 vaccine at the Royal Palace in Fez. Credit:AP

“To prevent absolutely no re-expression of the virus or transmission of the disease would be a huge challenge for any vaccine,” he said. “So, we must accept there is some risk of transmission, though we did observe much less virus shedding from the nose in vaccinated animals, in our study.”

Given that, he said it was more important to focus on the vaccines’ ability to protect against death and serious illness rather than efficacy.

“Are we preventing serious illness? Because that is what is causing the biggest impact,” he said.

AstraZeneca’s vaccine uses a viral vector – a modified chimpanzee virus that infects cells – causing them to produce SARS-CoV-2’s spike protein.

Unfortunately, this means human immune systems generate immunity to both SARS-CoV-2 and the viral vector, potentially limiting the ability of AstraZeneca to offer boosters to cover viral variants.

“Eventually, those antibodies may block the adenovirus vector from getting inside the cell to make the spike protein,” said Associate Professor Corey Smith, head of translational and human immunology at the QIMR Berghofer Medical Research Institute in Brisbane.

“It may still be OK, but that’s also an unknown. The big possibility is the other vaccine platforms may offer more long-term options against viral variants.”

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2021-02-08 07:06:00Z
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