A Covid-19 vaccine may be rolled out by March 2021 to the most vulnerable, which along with other advances could fundamentally change the course of the pandemic, a senior World Health Organization (WHO) official said on Monday.Bruce Aylward also told the WHO’s annual ministerial assembly that interim results announced from Pfizer Inc’s late-stage vaccine trials were “very positive”.“There is still much work to be done, this is just interim results...but some very positive results coming today which should hold great promise hopefully for the entire world as we move forward,” Aylward told the 194-member state forum.Pfizer said its experimental Covid-19 vaccine with partner BioNTech was more than 90% effective.WHO Director-General Tedros Adhanom Ghebreyesus tweeted shortly afterwards: “We welcome the encouraging vaccine news from @pfizer & @BioNTech_Group & salute all scientists & partners around the who are developing new safe, efficacious tools to beat #Covid19.’Aylward, referring to all three pillars of the ACT (Access to Covid Tools) Accelerator launched in April, said: “In diagnostics we are in a position to massively expand testing globally, in therapeutics we have sufficient tools right now to substantially reduce the risk of dying from this disease and in the area of vaccines - with the news of today especially - we are on the verge of having the readiness in place to roll out doses for high-risk populations in the late first quarter, early 2nd quarter.”However, he warned that an “acute funding gap” of $4.5 billion could slow access to tests, medicines and vaccines in low- and middle-income countries.