A limited supply of COVID-19 vaccines could be available before the end of 2020, the US’ Centers for Disease Control and Prevention (CDC) said.

“Many vaccines are being developed and tested, but some might be ready before others – CDC is planning for many possibilities,” the agency said in a statement on Wednesday.

It said the safety of any possible vaccine is a top priority and supply of a successful vaccine would be increased over months.

In case of limited supply, the CDC said “some groups may be recommended to get a COVID-19 vaccine first” and experts are working on how to distribute them in “a fair, ethical, and transparent way.”

On Tuesday, the National Institutes of Health, the main US agency responsible for biomedical and health research, said it had started a study to determine whether certain approved drugs show promise against COVID-19.

It said experimental antiviral drug Remdesivir has demonstrated clinical benefit for patients.

US President Donald Trump was also administered the drug when he was hospitalized after testing positive for virus.

The Trump administration’s Operation Warp Speed aims to deliver millions of doses of a COVID-19 vaccine by the end of 2020.

In July, the US government agreed to pay Pfizer and BioNTech $1.95 billion for 100 million doses of their vaccine, if it proves to be safe and effective.

It also has a $1.6 billion agreement with Novavax to manufacture and deliver 100 million doses by January 2021.

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