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AstraZeneca-Oxford Covid-19 Vaccine: What Has Been Said About Dosage and Efficacy


India’s drug regulator on Sunday gave final approval for the emergency use of a two-dose coronavirus vaccine, Covidshield, developed by AstraZeneca and the University of Oxford. The regulator did not dispute the recommended intervals between shots.

Authorities in Britain, the first to authorize the Covid-19 vaccine, recommended on Wednesday giving as many people as possible a first dose immediately and followed by a second injection four to 12 weeks later.

The differences in the findings are described below.



The AstraZeneca late stage trial was designed for two injections four weeks apart.

But in late-stage trial data published in The Lancet on December 12, the company said that most of the participants had delays in receiving their second injection.

The median time between two standard doses in UK volunteers was about 10 weeks and six weeks in Brazil, he said.


In late-stage trials, two full doses were given to most participants in the UK and Brazil and were shown to be 62% effective, but a smaller group of volunteers accidentally received half a dose followed by one dose complete, and Efficacy of 90% was recorded. They were in Great Britain and they were under 55 years old.

Many regulators set 50% as the minimum efficacy rate, but the Pfizer-BioNTech and Moderna vaccines achieved more than 90% in their trials.

AstraZeneca said last month that it did not know the reason for the higher efficacy rate, but was preparing further evidence to confirm whether the half-dose regimen could be 90% effective.

A single dose was considered to be 64% effective.

UK regulator


The UK Medicines and Healthcare Products Regulatory Agency (MHRA) has approved a two full dose regimen.

The Joint Committee on Vaccination and Immunization recommended that people receive one dose followed by a second four to 12 weeks later in an attempt to speed up the vaccination schedule.


On Wednesday, authorities cleared up a question raised by AstraZeneca-Oxford data, saying that a 90% success rate for a half dose followed by a full dose had not stood up to analysis.

The vaccine can be 80% effective when there are three months between injections, an official involved in the approval of the vaccine in Britain said in a briefing, higher than the average that the developers themselves had found.

Later in the same briefing, a British scientist involved in the approval of the vaccine said that one dose of the vaccine is around 70% effective after 21 days and before the second dose is administered.

Wei Shen Lim, chairman of Covid-19 immunization for the Joint Committee on Vaccination and Immunization, said that data from that finding was shared with the regulator, but was not “completely in the public domain.”

Regulator of India


India’s Comptroller General of Medicines VG Somani, who heads the Central Organization for Medicines Standards Control, approved a comprehensive two-dose regimen.

In announcing the approval on January 3, Somani did not clarify the intervals between shots. Sources told Reuters the doses would be administered four weeks apart.


Somani said the overall efficacy of the AstraZeneca vaccine was 70.42%, based on studies conducted abroad on 23,745 participants 18 years of age and older. Phase II / III clinical trials in 1,600 participants in India showed data “comparable to that of clinical studies abroad”.

Hindustan Times