In April, during the height of the coronavirus lockdown, Trump administration health experts hailed a test that would confirm if someone had already had the virus and therefore couldn't get sick again.
The antibody test would show who might have "the wonderful, beautiful immunity," President Donald Trump said was needed to get the nation working again.
Months later, the tests exist but haven't fulfilled their promise of allowing Americans to reclaim their lives, said Dr. Jennifer Rakeman of New York City's Public Health Laboratory.
In fighting off the virus, the body makes antibodies, which the tests measure. Unfortunately, scientists are still figuring out how well and for how long antibodies provide the immunity that protects against another infection by the coronavirus.
In truth, "there's no easy path to this knowledge" about immunity, Marc Jenkins of the University of Minnesota said. Long-term human or animal studies are usually needed to reach answers about immunity. Much of that work is done by the National Institutes of Health and universities, but they are occupied developing a vaccine against the coronavirus.
Until more is known, antibody tests should not be used to determine when it is safe to return to work or school, says the Centers for Disease Control and Prevention and the American Medical Association.
But the tests are useful in large studies to see how widely the coronavirus has spread and to screen people who have recovered and could donate their blood plasma for use as a treatment for those in the throes of COVID-19, the disease caused by the coronavirus.
WHO: Learn from pandemic
Earlier Monday the World Health Organization (WHO) said that countries that built up their health care systems in recent years fared better amid the COVID-19 pandemic.
In his daily briefing, WHO Director-General Tedros Adhanom Ghebreyesus urged countries to learn from the current pandemic to prepare for the next one. He praised Thailand, Mongolia, Senegal and other countries for their response to the virus.
"Many of these countries have done well because they learned lessons from previous outbreaks of SARS, MERS, measles, polio, Ebola, flu and other diseases," he said. "That's why it's vital that we all learn the lessons this pandemic is teaching us."
Meanwhile on Monday, India passed Brazil as the country with the second-highest number of confirmed coronavirus cases.
The Indian health ministry reported a record 90,802 new cases Monday, for a total of more than 4.2 million since the outbreak began. India also added 1,016 deaths Monday, pushing its overall toll to 71,642.
Brazil reported 14,521 new cases on Sunday, and while it now trails India in terms of overall cases, at 4.1 million, the country still trails only the United States in terms of deaths with 126,960.
As of Monday, the United States leads the world with about 6.3 million confirmed cases and more than 189,000 deaths, according to the Johns Hopkins University Coronavirus Resource Center.
In Australia, officials in the state of Victoria said Monday there were 41 new cases, the lowest single-day increase since late June.
Victoria has been battling to contain what has been the biggest outbreak in Australia. Authorities instituted lockdown restrictions in early August, and with the progress seen since then, announced Sunday some relaxation of the rules.
Prime Minister Scott Morrison also said Monday that Australia has an agreement in place with the biotech company CSL to manufacture two coronavirus vaccines, should they prove to be safe and effective in trials.
One potential vaccine is being developed by CSL and is set to move into stage two clinical trials later this year.
The other vaccine is a joint project between AstraZeneca and Oxford University currently in late-stage trials. Morrison said Monday that CSL will manufacture that vaccine as well for distribution in Australia, and that he expects 3.8 million doses to be available in January or February 2021.
Israel is beginning partial nighttime lockdowns in 40 cities and towns with the country's highest infection rates. Schools in those areas will also be closed, and gatherings will be limited to 10 people inside and 20 outdoors.
"I know that these restrictions are not easy but in the current situation there is no avoiding them," Prime Minister Benjamin Netanyahu said in a statement.