Tests have been delayed and in short supply as the United States surpassed 5.4 million cases, leaving many uncertain about their risk of spreading the virus. And as researchers rush to develop vaccines, they've had little evidence to tell if antibodies that protect against Covid-19 last long enough to get the virus under control. But developments from researchers Monday brought optimistic outlooks to both fronts.

SalivaDirect, a test that does not require specialized supplies and can deliver results in less than three hours, could be available to the public in a matter of weeks, according to Anne Wyllie, an epidemiologist at Yale School of Public Health who was part of the team responsible for the protocol.

And though many are in early stages and have not been peer-reviewed, a recent batch of studies show that humans -- even those with mild symptoms -- have a "robust" immune response to coronavirus that could provide evidence that a vaccine could protect the public for more than just a short period of time, said Dr. Ian Lipkin, director of the Center for Infection and Immunity at Columbia University Mailman School of Public Health.

"This is very good news and it's optimistic," said Lipkin. "You know, it is a bit of blue sky that we've been looking for."

How long that protection lasts is still unclear, but the studies indicate it could last for months.

The news comes as the White House coronavirus task force coordinator said Monday she wished the early days of coronavirus in the US looked more like it did in Italy: strict lockdowns keeping people home as infections spread.

And Surgeon General Dr. Jerome Adams said that even if testing improves, the nation needs to stick with prevention efforts.

"We can't test our way out of this problem," Adams said. "We need to lean on prevention, and that's making sure everyone's wearing a mask, washing their hands, and watching their distance from others."

US has the worst response of any major country, expert says

The United States' response to the virus isn't just lacking, director of the Harvard Global Institute of Health Dr. Ashish Jha said Monday, it's the "worst response of any major country."

"We didn't get here overnight. This has really been one mishap after another," Jha said. "The single factor that really differentiates us from everybody else is denialism that has pervaded our entire approach."

Even once the public and federal government got on board with the existence of the virus, many downplayed its severity, Jha said. And now, they believe a vaccine will soon end the pandemic in just two months, which Jha said is not the case.

But there was no good excuse for the lack of response because the US has been preparing for a pandemic just like this, a former US Food and Drug Administration commissioner said Monday.

"There have been efforts now over a number of decades, truly, to better prepare our nation against a range of biological threats, to invest in certain critical resources, but also to practice against simulations of threats," former FDA commissioner