Nurse preparing Pfizer vaccine. | Allesandro Di Marco

The Pfizer/BioNTech Covid-19 vaccine is highly effective for at least six months after the second dose and also works against the South African variant of the virus, according to a new study.

No significant safety concerns were found during a follow-up with volunteers who participated in the vaccine trials, the companies said in a statement.

"It is an important step to confirm the high efficiency and good security data so far, especially in the longer-term follow-up," said BioNTech Chief Executive, Ugur Sahin.

The Pfizer vaccine is 91.3% effective against Covid-19 for up to six months after the second dose and a 100% effective in preventing severe cases, as defined by the Control Centres and US Disease Prevention and 95.3% effective against severe disease, if the definition of the US Food and Drug Agency is used, which is different.

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The study contains data from more than 46,000 volunteers who participated in clinical trials.

Amongst them were 927 confirmed cases of coronavirus, 850 who received a placebo and 77 who received the vaccine. Of the total infected, 32 in the placebo group developed a serious disease, as defined by the CDC.

The study also showed that the vaccine was 100% effective against the South Africa variant, albeit in a smaller group of 800 participants.

"The high efficacy of the vaccine observed up to six months after a second dose and against the prevalent variant in South Africa offers more confidence in the overall effectiveness of our vaccine," said Pfizer CEO, Albert Bourla.

The Pfizer vaccine was the first to be authorised in the West and is used in immunisation programmes all over the world.