Oxford-AstraZeneca: How Efficient Is It? What’s the Dosage Needed?

Oxford vaccine: What do we know about the Oxford-AstraZeneca vaccine so far? How does it work? Find out here.

3 min read
Oxford-AstraZeneca: How Efficient Is It? What’s the Dosage Needed?

India is set to kick-off its vaccination drive from 16 January after the COVID-19 vaccine developed by Oxford University and pharma major AstraZeneca was one of the two vaccines to receive emergency use approval in India.

The Oxford vaccine can be stored in a standard fridge unlike the extreme cold storage requirements (-70 degree C) of the Pfizer-BioNtech candidate.

In India, the vaccine is also being produced under the name 'Covishield' by the Serum Institute of India (SII). It has been developed at SII's laboratory in Pune with a master seed from Oxford University/AstraZeneca.

Here’s a rundown of everything you need to know about the vaccine.


What does this approval mean for India?

For India, this is a great start to the new year!

SII had applied for emergency use authorisation to India's drug regulator earlier this month. SII had submitted additional data required by the Drug Controller General of India (DCGI) for determining the safety and immunogenicity of its COVID-19 vaccine candidate.

Adar Poonawalla, the company CEO, said on Monday, 28 December, that the firm is ready with a stockpile of around 40-50 million doses of the COVID-19 vaccine ‘Covishield’.

He had said that once regulatory approvals come through, “it'll be down to the government to decide how much they can take and how fast. We will be producing around 300 million doses by July 2021.”

“India is a part of COVAX. We will keep giving 50 percent of everything we make to India and to COVAX at the same time,” he said.

“Initially for the first month, we may give most of the volumes to India, because, in order to export, we have to go through the WHO pre-qualification procedure, which may take another month or so after it is licenced in India. That way, India will have priority,” he added.

“India has such a large population that we will probably end up giving the majority of those 50 million doses to India first.”
Adar Poonawalla

How does this vaccine work?

The Oxford-AstraZeneca vaccine is based on a common cold virus found in chimpanzees. Scientists have tweaked this virus to carry genetic material that contains instructions for the spike protein of the novel coronavirus. Once in, they start producing the coronavirus' spike proteins, forcing our body to mount an immune response via both neutralising antibodies and killer T cells, that squash the infected cells.

How efficient is it?

The initial results published by Oxford-Astra-Zeneca showed that the vaccine was 62.1 percent efficacious in participants who received two standard doses, while it had 90 percent efficacy in participants who received a low dose followed by a standard dose. The findings were that there was 70 percent overall efficacy.

Virologist Dr Jameel says that while Oxford vaccine data is promising, it's still not as exciting as Pfizer and Moderna's efficacy of nearly 95%. However, there's a lot of science that indicates it still is very good news.

How many doses do you need to take?

Oxford vaccine was given in two different dosages: One set received a ‘low’ shot as the first dose and a ‘high’ shot as the second dose. The second set received ‘high’ doses both times. He says it’s surprising that the low dose produced better efficacy of 90 percent than a high dose that received an efficacy of 62 percent.

"90 percent is great, but I would any day take a vaccine that offers better coverage," said Dr Jameel. Expanding on it, he said, if there is a vaccine that offers 70 percent efficacy but a 90 percent coverage, it's a better bet for a country. Reasonable efficacy but a good coverage is very important, he adds.


Is the vaccine safe?

According to data from The Lancet, 21 days after the first dose - but it is not clear in which trial from which country - there were “ten cases hospitalised for COVID-19, all in the control arm; two were classified as severe COVID-19, including one death.”

There were also 74 341 person-months of safety follow-up after the first dose (median 3.4 months) and 29,097 person-months of follow-up after two doses (median 2.0).

175 severe adverse events occurred in 168 participants, 84 events in the ChAdOx1 nCoV-19 group and 91 in the control group. Out of these, three events were classified as possibly related to a vaccine: one in the ChAdOx1 nCoV-19 group, one in the control group, and one in a participant who remains masked to group allocation. One case of the neurological disorder transverse myelitis may be linked to the shot, as per The Lancet.

(The article was first published in FIT and has been republished with permission)

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