DUBAI — The race to develop a vaccine that would end the coronavirus pandemic is accelerating as several firms move to clinical trials — but the World Health Organization (WHO) has warned that it is unlikely we will have a vaccine before the end of 2021. The development and mass distribution of a vaccine is widely seen as the most likely way to bring the coronavirus pandemic under control. Governments across the world have pumped money into vaccine research as pharmaceutical companies, startup businesses, universities, and research institutes work night and day to develop a vaccine. Three of the US' biggest pharmaceutical companies — Inovio, Moderna, and Pfizer — have already started clinical trials, seen as the first stage of developing a vaccine. In the UK, researchers at Oxford University supported by the government have said they are aiming to produce a vaccine by the autumn. While some may find hope in the fact that vaccines have reached the trial stage, which means they are being tested on humans to see if they work, senior WHO official Dale Fisher warned this week that a vaccine is unlikely to be available until the end of 2021. "I think end of next year is a very reasonable expectation," said Fisher, who is the chair of the WHO's Global Outbreak Alert and Response Network, during an interview with CNBC on Monday. "People need to have their expectations checked, I think, rather than blindly, hopefully doing what you want because you want it," he added. This is because the vaccines currently under clinical trials are in Phase 1 of the development process, but must go through Phase 2 and 3 of trials to ensure they are safe and reliable. Even once a vaccine is found to be suitable, it will then need to be mass produced and mass distributed — a potentially lengthy process in itself. US President Donald Trump has taken an optimistic tone on the development of a vaccine and said this week that he was confident there would be one available by the end of this year. "We are very confident that we are going to have a vaccine at the end of the year, by the end of the year," Trump said in a recent Fox News town hall in Washington. "We think we are going to have a vaccine by the end of this year, and we are pushing very hard." However, Fisher joined most health experts in dismissing this timeline as unrealistic, describing Trump's comments as "a bit premature." His concerns were shared by the CEO of Roche, a major pharmaceutical company in the US. "I have no doubt that as so many companies are working on a vaccine in parallel, and as we see such great collaboration with regulators including the FDA, we can actually speed up the approval of vaccines," Roche CEO Severin Schwan said to CNBC on Monday. "But still, typically it would take years to develop a new medicine," he added. "Most experts agree that it will take at least 12 to 18 months until we see a vaccine which is available in the necessary quantities for patients." — Al Arabiya English