This is everything you need to know about the Oxford/AstraZeneca coronavirus vaccine, which was approved for use in the UK in December 2020.
It was the second Covid-19 vaccine to be approved by the medicines regulator.
How does it work?
The Oxford/AstraZeneca vaccine – called ChAdOx1 nCoV-19 – uses a harmless, weakened version of a common virus which causes a cold in chimpanzees.
Researchers have already used this technology to produce vaccines against a number of pathogens including flu, Zika and Middle East Respiratory Syndrome (Mers).
The virus is genetically modified so that it is impossible for it to grow in humans.
Scientists have transferred the genetic instructions for coronavirus’s specific “spike protein” – which it needs to invade cells – to the vaccine.
When the vaccine enters cells inside the body, it uses this genetic code to produce the surface spike protein of the coronavirus.
This induces an immune response, priming the immune system to attack coronavirus if it infects the body.
How many doses do I need?
There are two doses of the vaccine needed. They are given up to 12 weeks apart.
Both are injected into the upper arm.
The Medicines and Healthcare products Regulatory Agency (MHRA) has authorised two full doses of the Oxford vaccine, with the second dose given four to 12 weeks after the first.
It said data showed the vaccine was up to 80 per cent effective when there was a three-month interval between the first and second doses.
A first dose of the jab gives around 70 per cent effectiveness from three weeks after immunisation until a second dose at 12 weeks, according to the MHRA and the Joint Committee on Vaccination and Immunisation (JCVI).
Professor Wei Shen Lim, from the JCVI, said that people acquire a high level of protection after a first dose.
He said the JCVI therefore recommends that delivery of an initial dose should be prioritised for both the AstraZeneca and Pfizer vaccines.
Will it stop transmission?
Not much is known about whether the jabs stop transmission of the virus, but data from the University of Oxford suggests the AstraZeneca vaccine may reduce transmission by 67 per cent.
How long does immunity last?
This is not yet known, but it is thought it will be at least a year.
Researchers agree it is likely people will need to be re-vaccinated every year to ensure they are protected.
Is it effective against the new variants that have emerged?
Researchers found that the Oxford/AstraZeneca vaccine is "effective" at fighting the UK variant that was first discovered in Kent.
Oxford University researchers who developed the vaccine say it has a similar efficacy against the variant, compared with the original strain of Covid-19 against which it was tested.
The pre print also describes analysis which suggests vaccination with the Oxford/AstraZeneca jab results in a reduction in the duration of shedding and viral load, which may translate into a reduced transmission of the disease.
Andrew Pollard, professor of paediatric infection and immunity, and chief investigator on the Oxford vaccine trial, said: “Data from our trials of the ChAdOx1 vaccine in the United Kingdom indicate that the vaccine not only protects against the original pandemic virus, but also protects against the novel variant, B117, which caused the surge in disease from the end of 2020 across the UK.”
The emergence of the mutation, first detected in Kent and the south-east of the England, was partially blamed for the rapid spread of the virus, and increase in cases, before lockdown was imposed across the country in January.
Between October 1 last year and January 14 this year, researchers used swabs taken from volunteers with both symptomatic and asymptomatic infection enrolled in a phase two or three vaccine efficacy study.
They looked at the data to work out which strain of the virus the participants had been infected with after receiving either the vaccine or the control.
According to the scientists, the protection against symptomatic infection was similar despite lower neutralising antibody titres (a measurement of how much antibody has been produced) in vaccinated individuals against the new UK variant (B117) than the non-B117 strain.
The study, which has not been peer-reviewed, reports that vaccine efficacy against symptomatic positive infection was similar for B117 and non-B117 lineages, at 74.6 per cent and 84 per cent respectively.
How has it been developed so quickly?
In the past it has taken years, sometimes decades, to produce a vaccine.
Traditionally, vaccine development includes various processes, including design and development stages followed by clinical trials – which in themselves need approval before they even begin.
But in the trials for a Covid-19 vaccine, things look slightly different. A process which usually takes years has been condensed to months.
While the early design and development stages look similar, the clinical trial phases overlap, instead of taking place sequentially.
And pharmaceutical firms have begun manufacturing before final approval has been granted – taking on the risk that they may be forced to scrap their work.
The new way of working means that regulators around the world can start to look at scientific data earlier than they traditionally would do.
