The first participant in a clinical trial for a vaccine to protect against the new coronavirus will receive an experimental dose on Monday, according to a US government official.
The National Institutes of Health is funding the trial, which is taking place at the Kaiser Permanente Washington Health Research Institute in Seattle.
Public health officials say it will take a year to 18 months to fully validate any potential vaccine.
Testing will begin with 45 young, healthy volunteers with different doses of shots co-developed by NIH and Moderna Inc.
There is no chance participants could get infected from the jabs, because they do not contain the virus itself.
The goal is purely to check that the vaccines show no worrisome side effects, setting the stage for larger tests.
Dozens of research groups around the world are racing to create a vaccine as Covid-19 cases continue to grow.
Importantly, they are pursuing different types of vaccines — jabs developed from new technologies that not only are faster to produce than traditional inoculations but might prove more potent.
Some researchers even aim for temporary vaccines, such as jabs that might guard people’s health a month or two at a time while longer-lasting protection is developed.
Also in the works: Inovio Pharmaceuticals aims to begin safety tests of its vaccine candidate next month in a few dozen volunteers at the University of Pennsylvania and a testing centre in Kansas City, Missouri, followed by a similar study in China and South Korea.
Even if initial safety tests go well, “you’re talking about a year to a year and a half” before any vaccine could be ready for widespread use, according to Dr Anthony Fauci, director of NIH’s National Institute of Allergy and Infectious Diseases.
That still would be a record-setting pace. But manufacturers know the wait — required because it takes additional studies of thousands of people to tell if a vaccine truly protects and does no harm — is hard for a frightened public.
US president Donald Trump has been pushing for swift action on a vaccine, saying in recent days that the work is “moving along very quickly” and he hopes to see a vaccine “relatively soon”.
Today, there are no proven treatments.
In China, scientists have been testing a combination of HIV drugs against the new coronavirus, as well as an experimental drug named remdesivir that was in development to fight Ebola.
In the US, the University of Nebraska Medical Centre also began testing remdesivir in some Americans who were found to have Covid-19 after being evacuated from a cruise ship in Japan.
For most people, the new coronavirus causes only mild or moderate symptoms, such as fever and cough.
For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia.
The worldwide outbreak has sickened more than 156,000 people and left more than 5,800 dead.
The vast majority of people recover.
According to the World Health Organisation, people with mild illness recover in about two weeks, while those with more severe illness may take three weeks to six weeks to recover.