Fact Check-Experts say the Oxford AstraZeneca COVID-19 vaccine is safe and that its benefits far outweigh possible risks

A tweet suggesting a vaccine for COVID-19 is not safe and is still being tested on the public is missing crucial context in its claim. The vaccine has gone through a trial process before being released and regulators have repeatedly said it is safe and effective. The user did not mention a vaccine by name, but it is likely he was referring to the Oxford/AstraZeneca vaccine – the rollout of which was halted in several countries after reports of side-effects.

The tweet was originally posted to an account that no longer exists (; however, a screenshot has since circulated on Facebook (here). It reads: “If the 'vaccine' was absolutely safe and absolutely sufficiently tested as we were told, why has it been stopped now in 16 countries? Surely all that testing they did beforehand would have highlighted these problems? Oh that's right-this IS the test isn't it [sic]”.

The rollout of the Oxford/AstraZeneca vaccine was halted in several countries after reports of side-effects, including a small number of unusual blood clotting disorders (here). Many of the countries, mostly in Europe, have since resumed using the jab after European regulators said a preliminary review found there was no overall increase in risk of blood clots. (here). The same regulators, from the European Medicines Agency (EMA), have repeatedly said the vaccine’s benefits in protecting people from the threat of COVID-19 outweighed the possible risks (here).

The World Health Organisation (WHO) has also said the vaccine is safe to use while research is ongoing to examine possible links to rare blood clots. This is because the disorder is so unusual it might only affect “one in a million” vaccine recipients, WHO assistant director-general Mariangela Simao said (here).

On March 29, scientists released a preprint of a study into the cause of the clots, which found they could be a result of a specific immune system response resembling heparin-induced thrombocytopenia (HIT), a known blood disorder that is treatable when discovered promptly (here, here, here).

The tweet casts doubt on the level of testing of the vaccine, but all approved COVID-19 vaccines have undergone the standard three-phase trial process to determine safety and efficacy. It is then normal practice to continue monitoring the vaccine during the subsequent rollout (here).


Missing context. Investigations are underway into a possible link between the Oxford/AstraZeneca vaccine and a blood clotting disorder – but the incidence rate is so unusual that regulators have said the benefits of the shot would outweigh any risks. It is not accurate to say the vaccine is still being tested on the population. All approved COVID-19 vaccines have undergone the normal three-phase trial process and it is standard practice to continue monitoring during a rollout.

This article was produced by the Reuters Fact Check team. Read more about our fact-checking work here .