GENEVA, May 27 (Xinhua) -- The World Health Organization (WHO) said on Wednesday that no empirical evidence has been found on cross protection, a phenomenon in which a pre-existing viral infection prevents a secondary infection with the same or closely related virus, against COVID-19, but studies in this area may offer hope for long-term protection.

"There is certainly some evidence with regard to T-cells that if you have a previous coronavirus infection, you may be able to mount a more rapid response to COVID-19. But there is no empirical evidence that the previous coronavirus infections protect you from infection with COVID-19," Michael Ryan, executive director of the WHO Health Emergencies Program, said in a press conference on Wednesday in Geneva, responding to a question on the theory of cross-protection against COVID-19.

"The jury is still very much out on that. But it is interesting to know that, at least in some of the studies, if we get a more broad-based T-cell response, there's more hope for vaccines and others producing a more long-term immune response." he said.

"So for me this information is very important. It gives us hope that we're getting the kinds of immune responses that may be helpful for long-term protection and may also mean that vaccines have a broader protection," he added.

"This is something that is under development. But yes, so the results from the T-cell is welcomed news, and we know that there are a number of labs that are additionally looking at that as well," added Maria Van Kerkhove, technical lead COVID-19, WHO Health Emergencies Program.