Hailed as a cheap, easy-to-store not-for-profit vaccine, the AstraZeneca shot has suffered a litany of setbacks.
In the latest, several countries advised that the world's most used jab should not be given to under-30s due to the risk of blood clots after 19 people died in Britain.
The British laboratory made headlines in November when it claimed its jab could match the 90% effectiveness of the rival and much more expensive Pfizer/BioNTech jab, which has to be kept at extremely low temperatures.
But that success rate was only if half a dose was given for the first shot with a full second dose a month later.
However, it later emerged that these results were obtained by accident when a half dose was given by mistake, raising questions about the robustness of the tests.
On average, trials showed it to be about 60% effective, though in real-world conditions it has so far performed much better.
The Anglo-Swedish drug company was accused of bad faith by European leaders in January over massive shortfalls in the delivery of vaccines to EU countries while millions of Britons were getting the shot.
The stand-off prompted the EU to slap export controls on vaccines and send inspectors into a plant in Belgium where the firm said it was having production problems.
Livid that AstraZeneca would only be able to deliver one-third of the promised 120 million vaccines in the first quarter, Brussels threatened to trigger an emergency clause in the Brexit deal before quickly backtracking.
Governments' mixed messages
When the EU experts finally approved the shot, health officials in a number of states including France and Germany refused to authorize it for over 65s.
Faced with vaccine shortages, both countries as well as Italy later made it available to some older people with serious health risks.
By then the bloc was facing rising skepticism about the shot, with some people refusing the jab even as the EU suffered shortages.
S.Africa sends back doses
While AstraZeneca and many scientists said the jab had been the victim of unfair coverage, the bad news just kept coming.
South Africa asked to send back one million doses after scientists found it gave "minimal protection" against mild and moderate cases of the country's more contagious virus strain.
Not a charity
The vaccine won plaudits initially for its non-profit stance, but last March, Oxford University, which developed it, backed off its pledge to donate the rights to any drugmaker.
AstraZeneca said it would provide doses on a cost basis for as long as the pandemic lasts. But it was later accused of reneging on this when it emerged that it could hike the price as early as July.
Blood clot worries
The latest problem emerged last month when several countries suspended their campaigns -- most temporarily -- after a reported link with blood clots.
But after further examination the European Medicines Agency (EMA), the EU's drugs regulator, said Wednesday that clots were "very rare" and the vaccine's benefits outweigh the risks.
It had earlier said that severe allergies should be added to its list of side effect warnings.
Britain said it had recorded 79 cases of blood clots from the more than 20 million doses of the vaccine given there, with 19 deaths.
The World Health Organization insisted the clots were "very rare" and said a link with the vaccine was "plausible but not confirmed."
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