The World Health Organization warned on Monday that, despite strong hopes for a vaccine, "there is no silver bullet at the moment, and there might never be."
The director-general of the WHO said there were concerns that vaccines might not prove effective, or that they might convey protections for just a few months.
He said for now, stopping outbreaks hinged on the difficult task of testing, tracing, and social distancing.
According to a Reuters tally more than 18 million people around the world are reported to have been infected with the disease and 688,000 have died.
With cases spiraling globally, the fatality rate appears to hover somewhere below one percent. But Maria Van Kerkhove, the WHO's lead technical expert on COVID-19, emphasized that number still reflects a global cause for alarm.
"That may not sound like a lot, but it is quite high if you think about a virus that can transmit readily, that can transmit well."
The UN body's emergencies programme director said that nations with particularly high transmission rates such as Brazil and India needed to gird themselves for a grinding fight against the novel coronavirus.
"The way out is long, and it requires a sustained commitment to doing many, many, what on the face are very simple things but are difficult to actually implement."
The United States remains the global epicenter of the pandemic, with more than four-and-a-half million cases and north of 155,000 deaths.
"It's not our job to tell the U.S. what it should be doing at the subnational level."
The WHO declined to comment on Washington's response to the crisis, but said that while the science was clear, leaders weren't always willing to listen.
"The difficulty for us all is sometimes we know the right path, the difficulty is choosing to walk it."