San Francisco, Jul 23 (IANS): People might have to take multiple doses of a potential Covid-19 vaccine to protect themselves from the disease, said Microsoft Co-founder Bill Gates.

The billionaire philanthropist told CBS News on Wednesday that "none of the vaccines at this point appear like they'll work with a single dose."

Over 150 Covid-19 vaccines are currently at different stages of development, with a few now advancing to the late stage clinical trial.

The Bill and Melinda Gates Foundation has donated $300 million towards the global effort to beat Covid-19.

In a blog post, Gates had earlier said that developing a safe and effective vaccine is an urgent need to combat the pandemic.

"We need to make billions of doses, we need to get them out to every part of the world, and we need all of this to happen as quickly as possible," he wrote.

The world will need to manufacture and distribute at least seven billion doses of the vaccine -- or possibly 14 billion, if it is a multi-dose vaccine - to beat the pandemic, he said.

This is because in order to stop the pandemic, the vaccine will have to be made available to almost every person, Gates said.