Timeline: AstraZeneca Covid-19 vaccine's roller-coaster ride

AstraZeneca published updated results from its major US Covid-19 vaccine trial, after health officials there publicly criticized it for using "outdated information" to show how well the immunization worked.

On Thursday, AstraZeneca said its Covid-19 vaccine was 76 per cent effective in the new analysis of the US trial, a tad lower than the level reported earlier.

Also Read | AstraZeneca says vaccine 76% effective in updated US trial data

Here's a look at the progress of the vaccine development to date since its inception.

January 2020:

A team involving Oxford Vaccine Group and Jenner Institute starts work on developing a vaccine to prevent Covid-19.

March 2020:

Researchers at the Oxford University begin screening healthy volunteers, aged 18-55, for recruitment in the ChAdOx1 nCoV-19 vaccine trial in the Thames Valley Region.

April 2020:

Human trials begin

AstraZeneca and Oxford join forces for development and potential large scale distribution of the vaccine candidate.

May 2020:

AstraZeneca and Oxford start recruiting volunteers for a much larger human trial in the UK.

July 2020:

Initial safety data released showed vaccine was safe and produced an immune response.

August 2020:

Vaccine candidate begins late-stage study in the United States.

September 2020:

AstraZeneca suspends global trials due to an unexplained illness in a study participant.

AstraZeneca resumes UK trials.

Oxford/AstraZeneca begin submitting data to the UK regulator under a rolling review process.

Also Read | AstraZeneca backs its Covid-19 shot as nations battle new surges

October 2020:

EU launches real-time review of the vaccine.

United States restarts trial, the last one to do so after other regions began resumption much earlier.

November 2020:

AstraZeneca confirms that the UK regulator has started an accelerated review of vaccine.

Interim late-stage data from UK, South Africa trials released:

The vaccine on average prevented 70 per cent of Covid-19 cases in late-stage trials in Britain and Brazil.

The success rate rose to 90 percent in a group of trial participants who accidentally received a half dose followed by a full dose.

The efficacy was 62 per cent if the full dose was given twice, as it was for most study participants.

December 2020:

Russia's sovereign wealth fund says AstraZeneca will begin clinical trials to test a combination of its experimental Covid-19 vaccine with Russia's Sputnik V shot in hopes to boost efficacy.

Britain approves shot in first for Covid-19 vaccines in the West. Regulators said that the higher efficacy seen in the half-dose/full-dose cohort was likely a result of a longer gap between doses, rather than the amount of vaccine given.

January 2021:

India approves Serum's vaccine days later in early January.

Europe gives vaccine green light in late January.

February 2021:

The World Health Organisation gives the vaccine a go-ahead.

March 2021:

AstraZeneca cut its first-quarter supply forecast to the EU due to export constraints.

Austria halts use of one batch of vaccine following reports of cases of blood clots in Nordic countries.

More than a dozen European countries, including Germany and France, followed suit and halted use of the vaccine.

Also Read | AstraZeneca to release more data on US trials soon

European regulators and WHO back vaccine's safety in mid-March, but poll shows European confidence has taken a hit.

In late March, interim data from late-stage trials in US, Peru, Chile shows vaccine is 79 per cent effective.

Just after, the US National Institute of Allergy and Infectious Diseases said the drugmaker may have included outdated information from the trial, providing an incomplete view of the efficacy data.

AstraZeneca issues clarification on interim study, adding that data was based on data through Feb. 17

Canada backs vaccine, but updates label to include information on blood clots.