The United States is likely to have enough safe and effective Covid-19 vaccines available to inoculate the most vulnerable Americans by the end of 2020, Health and Human Services Secretary Alex Azar said on Wednesday.

The US government is “cautiously optimistic” that one or two vaccines, likely from Pfizer Inc or Moderna Inc, will be available by the end of the year and can begin to be distributed to Americans, officials said during a news conference.

Azar said he expects all seniors, healthcare workers, and first responders will be able to receive a vaccine as soon as January, with the rest of the American public able to get a vaccine by April.

Also read:China’s province to hand out Covid-19 vaccine to non-priority groups as well

Companies participating in the US government’s effort to develop a vaccine for Covid-19, dubbed Operation Warp Speed, have begun developing manufacturing capabilities even before any vaccinations have been authorised by regulators.

In an open letter published last week, Pfizer said it is unlikely to have enough data to submit for a US regulatory authorisation until late November, after the US presidential election.

Also read:AstraZeneca Covid-19 vaccine: Volunteer dies, but the trial will continue, says Brazil

The coronavirus outbreak has been worsening in recent weeks as cold weather pushes Americans indoors, raising the chance of contracting the virus. Some 38 US states and two territories have reported rising case counts. More than eight million Americans have been infected with the novel coronavirus and more than two lakh have died.