Even as governors across the country plan to allow businesses to begin re-opening in May, officials and health experts are warning that Americans will still have to maintain proper social distancing measures for months.

“Social distancing will be with us through the summer to really ensure that we protect one another,” Dr Deborah Birx, the the Trump administration's coronavirus response coordinator, said on NBC's 'Meet the Press' on Sunday.

That's a more cautious message than the one Vice President Mike Pence sent just two days earlier in a podcast interview with conservative commentator Geraldo Rivera, during which he said he believes the US will "largely have this coronavirus epidemic behind us" by Memorial Day on 25 May.

Experts have warned of the potential for second and even third spikes in the number of cases and deaths from coronavirus later this year, saying that the possibility increases for a second wave of the pandemic if social distancing does not remain in some capacity.

In Colorado, Democratic Governor Jared Polis will begin loosening some restrictions on people physically going to work next Monday, but said workplaces still must maintain proper social distancing.

"Our target is about 60 to 65 per cent social distancing from the way people used to live, and how we can do that over a period of months in a psychologically sustainable way — and of course an economically sustainable way — that meets the health goals of the state," Mr Polis said on CNN on Sunday.

"We're all worried about the potential for a second spike, whether it's in the fall along with flu season ... [or] whether it's July," Mr Polis said.

Meanwhile, the World Health Organisation is taking no chances in its proclamations about how optimistic people should be about the near-term outlook on Covid-19, warning in a recent statement that even people who have contracted the disease previously may not be immune from catching it again.

"There is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection," WHO said.

Many Americans who have recently recovered from Covid-19 have been donating their plasma to health centres because it has antibodies that can "attack the virus," according to the Red Cross.

Ms Birx said WHO was being "very cautious" with its statement about the potential for re-infections.

Scientists and doctors have been using the plasma from donors who have recovered from the disease to help treat sick people and are assessing its impact in real time.

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"All that data together I think is going to create a very clear picture about antibody," Ms Birx said.