The US Centres for Disease Control and Prevention has asked states to prepare for Covid-19 vaccine distribution as soon as late October.
Documents published by the CDC on Wednesday show that vaccines would be made available first, free of cost, to high-risk groups – including healthcare workers, national security personnel and nursing home residents and staff.
The timing could not be more important politically, as an October arrival of the vaccine would come right before US President Donald Trump seeks re-election in November.
Covid-19 has killed more than 190,000 Americans and counting – and the Trump administration has poured billions of federal dollars into developing a vaccine.
"For the purpose of initial planning, CDC provided states with certain planning assumptions as they work on state-specific plans for vaccine distribution, including possibly having limited quantities of vaccines in October and November," a CDC spokeswoman told Reuters.
The country's top infectious disease expert Anthony Fauci told MSNBC on Wednesday that based on the patient enrolment rate in vaccine trials already under way, there could be enough clinical data to know by November or December whether one of the vaccines is safe and effective.
Regulators around the world have repeatedly said development speed would not compromise vaccine safety, as quicker results would stem from conducting parallel trials that are usually done in sequence.
Drug developers including Moderna, AstraZeneca and Pfizer are currently leading the race to develop a safe and effective Covid-19 vaccine.
The CDC documents describe two potential vaccine options, which match the profiles of candidates from Pfizer and Moderna.
The news came as a Trump administration official said that the US would not pay $80 million it owes the World Health Organisation and instead direct the money to pay its bill to the United Nations.
The United States plans to leave the Geneva-based WHO on July 6, 2021, after Mr Trump accused it of becoming a puppet for China during the coronavirus pandemic. The WHO has rejected Mr Trump's assertion.
"The United States has long been the world’s most generous provider of health and humanitarian assistance to people around the world. This assistance is provided with the support of the American taxpayer with the reasonable expectation that it serve an effective purpose and reach those in need," said State Department Spokeswoman Morgan Ortagus.
"Unfortunately, the World Health Organization has failed badly by those measures, not only in its response to Covid-19, but to other health crises in recent decades. In addition, WHO has declined to adopt urgently needed reforms, starting with demonstrating its independence from the Chinese Communist Party," she said.
Under a 1948 joint resolution of the US Congress, Mr Trump had to give one-year notice of the withdrawal from the WHO and is required to pay what Washington owes for the organisation's current fiscal year.
The United States currently owes the WHO $18 million for the financial year 2019 and $62 million for the financial year 2020.
Ms Ortagus said the US would also scale down its engagement with the WHO by recalling representatives based in the organisation's headquarters and at regional offices.
Former vice president Joe Biden has said the United States will re-join the WHO if he defeats Mr Trump in the presidential election in November.
While countries continue to wait on a vaccine, increasing testing capacity is seen as key to controlling the virus.
Britain said it was investing in trials of a 20-minute Covid-19 test, with a view to rolling out widespread, systematic testing to detect outbreaks early, amid criticism over backlogs in its current testing system.
Health Minister Matt Hancock has said he hopes mass testing using faster Covid-19 tests can be rolled out towards the end of the year, adding that they are key to restoring freedoms after months of restrictions.
"I want to solve the problem by having the next generation tests at a radically bigger scale. You can't do that on the current technology very easily," he told BBC television.
Britain is looking to develop tests which do not need to be read in a lab, giving results in a matter of minutes, rather than the current next-day target.
Meanwhile, South Korea said on Thursday that it would double its critical-care hospital beds after a severe shortage highlighted the strain the pandemic is having even on well-equipped countries.
The spike in serious cases, with older people making up an increasing proportion of patients amid a broader resurgence, marks a sharp turn for a country that was seen as successful in crushing one of the worst early outbreaks of the new coronavirus outside China.
Fewer than 10 intensive-care beds were available in the greater Seoul area, a metropolis of 26 million people, as of Tuesday, health authorities said.
The crisis is growing more acute as more than 40 per cent of the country's new coronavirus victims are 60 or older, up from 20 per cent a month ago, health authorities said.
