Brussels, March 12 : The European Union (EU) has authorised the use of a Covid-19 vaccine produced by Johnson & Johnson, only hours after the European Medicines Agency (EMA) made a positive recommendation based on scientific assessment of its efficacy and safety. Developed by Janssen, the pharmaceutical arm of Johnson & Johnson, it is the fourth vaccine the EU has granted the conditional marketing authorisation, after the ones developed by BioNTech-Pfizer, Moderna and AstraZeneca, reports Xinhua news agency. "More safe and effective vaccines are coming to the market," European Commission President Ursula von der Leyen tweeted on Thursday. "With the number of doses we ordered, we could vaccinate up to 200 million people in the EU." On Thursday afternoon, the EMA recommended the use of the Janssen vaccine among people over 18 years of age. It is also the first Covid-19 vaccine which can be used in a single dose, said EMA's Executive Director Emer Cooke. Results from a clinical trial involving 44,000 people in the US, South Africa and Latin American countries showed that the vaccine had a 67 per cent efficacy, according to the EMA. The EU has rolled out vaccination programs aiming at inoculating 70 per cent of its adult population by September 21, 2021. Meanwhile, 263 candidate vaccines are still being developed worldwide, 81 of them in clinical trials, according to the World Health Organization. /IANS