Dr Margaret Harris from the World Health Organization has said the process to develop a Covid-19 vaccine was sped up but "corners have not been cut".
Speaking on RTÉ's Morning Ireland she said the science that was needed was done before the outbreak, and also much of the knowledge came from other viruses like SARS.
She said regulators had also been doing their work before the final data and were ready to review it. Dr Harris has described the development of vaccines for the virus as "much wanted good news" before Christmas.
She does not envisage any major problems regarding the storage of the vaccines and certain temperatures required for some. "The Ebola vaccine that we have used in conflict zones is one that has to be stored also at -79