The woman in charge of procuring possible Covid-19 treatments for Britain has said a fully effective vaccine might never be developed, and that any early versions that do get approved might not work at all for some people, Reuters reported.

There is no clinically proven vaccine against the coronavirus, though nearly 200 candidates are in development worldwide, and late-stage trial results are expected for the first of them by the end of 2020.

“However, we do not know that we will ever have a vaccine at all. It is important to guard against complacency and over-optimism”, Kate Bingham, the chair of the UK Vaccines Taskforce, wrote in an article published overnight in The Lancet medical journal.

“The first generation of vaccines is likely to be imperfect, and we should be prepared that they might not prevent infection but rather reduce symptoms and, even then, might not work for everyone or for long.”