Many of the states moving most quickly to roll back rules designed to slow the spread of the novel coronavirus lack benchmarks that would require them to reimpose restrictions if infections spike.

That leaves governors who are anxious to jump-start their economies untethered to clear numerical standards, alarming even some of the top medical officials in their states, who warn that new outbreaks are on the horizon.

“There’s just a lot more that needs to be done,” said Scott Harris, Alabama’s chief health officer. “We still feel like we could do a better job with getting real-time information that would help us make those decisions. But we don’t have hard triggers at this point.”

Alabama is hardly alone. Georgia also has not built specific triggers into its reopening plan, though Candice Broce, a spokeswoman for Brian Kemp, said the Republican governor “would do whatever is necessary based on our data and the advice of public health officials.” In Tennessee, there is “no set threshold to reimpose certain restrictions, but they’re certainly on the table if we deem a reimposition needed,” said Gillum Ferguson, a spokesman for Gov. Bill Lee (R).

As nail salons, restaurants, and gyms began to reopen on May 15 in parts of Virginia, business owners and customers are proceeding with caution. (The Washington Post)

Colorado Gov. Jared Polis (D) has empowered local authorities to reimpose restrictions as they see fit. In Pennsylvania, there is not a “specific metric that would trigger further restrictions,” said Nate Wardle, a spokesman for the state health department, but officials are “looking at the case counts being reported, the contact tracing occurring and determining whether any of these steps need to be taken.”

Mark McClellan, a former commissioner of the Food and Drug Administration and administrator of the Centers for Medicare and Medicaid Services under President George W. Bush, said state leaders know “they may need to pause or even step back.”

“But we haven’t seen a whole lot of detail on those specific plans in most states,” said McClellan, a member of the advisory group assisting Texas Gov. Greg Abbott (R). “It’s going to be important as the reopening occurs to track key data and move quickly if there are signs of an increase in the reproduction rate of the virus.”

As more states reopen their economies stalled by the coronavirus, governors discuss the latest in the response on May 3. (The Washington Post)

Texas, two weeks after the beginning of its phased reopening, on Thursday reported a single-day high in cases of the coronavirus and deaths from covid-19, the disease it causes. McClellan said some of the upward trends were related to outbreaks in high-risk settings, such as nursing homes.

A spokesman for Abbott did not respond to a request for comment. Several officials in some of the other states pursuing aggressive reopening plans, such as Arizona and Florida, also did not respond.

Asa Hutchinson, the Republican governor of Arkansas, said this week he may pull the state back from the second phase of reopening, expected to begin Monday, after one of the biggest jumps Thursday in new cases of covid-19 since March. “This is not encouraging,” he told reporters Thursday.

The need for circuit breakers is on vivid display globally, as some of the countries initially able to contain the virus, from South Korea to Lebanon, have experienced new outbreaks, causing them to clamp down.

Seoul, which last week eased rules in anticipation of “a new daily life with covid-19,” shut bars and nightclubs after the discovery of a cluster of cases. German Chancellor Angela Merkel, who has a PhD in quantum chemistry, has required that restrictions be reinstated in any region that records more than 50 new cases for every 100,000 residents in a week.

No such specificity appears in the White House’s nonbinding guidelines for a phased reopening, which warn of “rebound” but do not establish parameters for measuring one. That has left states to decide on their own whether to build into their reopening plans rules that would compel them to snap restrictions back into place.

A few states have taken steps in that direction, but even these states often lack firm benchmarks.

Minnesota has a “Dial Back Dashboard” setting out key metrics — from a rise in covid-19 cases to the capacity for testing — informing decisions “about re-establishing restrictions to slow the spread of the virus.”

In California, Gov. Gavin Newsom (D) is relying on six “indicators for modifying the stay-at-home order,” one of which is the “ability to determine when to reinstitute certain measures, such as the stay-at-home orders, if necessary.” The state’s road map offers little about how to make that determination.

New York’s framework is among the most detailed, dividing the state into 10 regions and evaluating each by seven metrics, such as holding hospitalization rates below 2 per 100,000 residents and maintaining a testing rate of 30 per 1,000 residents.

If any measure is not met, “you have a circuit breaker, you stop,” Gov. Andrew M. Cuomo (D) said. “You close the valve on reopening.”

Illinois officials similarly split the state into four regions and laid out a five-phase plan with benchmarks that could require new lockdown measures in parts of the state. Triggers include sustained increases in the rate of people testing positive for the virus, increases in hospital admissions, reduction in hospital capacity and a significant regional outbreak.

Reimposing restrictions would be the “most difficult thing we would have to do,” said Anne Caprara, chief of staff to Gov. J.B. Pritzker (D). But having a clear plan backed by science would allow residents to understand the rationale, she said, and hopefully ease some of their anger.

Even the detailed guidelines adopted by certain states failed to satisfy some epidemiologists. Isaac Weisfuse, a Cornell University epidemiologist who was a deputy health commissioner in New York City during the H1N1 swine flu outbreak in 2009, said New York should expand its criteria to include earlier indicators, such as outpatient medical records for people who report “complaining of the signs and symptoms of covid-19” before they get seriously ill. He also suggested “behavioral surveillance,” in which officials track whether the public complies with relaxed measures designed to allow people more access to life outside their homes while still keeping the virus in check.

Many experts share Weisfuse’s concerns, saying the country still lacks the tools to predict a coming surge fast enough to fend off its escalation into an unmanageable outbreak. Many of the common metrics, such as hospitalizations and even rates of positive test results, lag far behind the actual transmission of the disease.

“We need a comprehensive battle strategy, meticulously implemented,” said Tom Frieden, former director of the Centers for Disease Control and Prevention.

Not all state health officials see specific benchmarks as necessary.

“We have very robust data — number of cases, cases in nursing homes, hospitalizations, people on ventilators — but at the end of the day, I practiced medicine for 30 years, and we treat the patient, not the chart,” said Randall W. Williams, director of the Missouri Department of Health and Senior Services. “There’s no one threshold. Every day, we analyze the data and take that into consideration.”

Clay B. Marsh, West Virginia University’s chief health officer and the state’s coronavirus coordinator, said officials are examining the rate at which the virus spreads and the seven-day rolling average of new cases in each county. A 50 percent increase in cases would be worrisome, he said, while a 75 percent increase would require designation as a high-alert county and give rise to recommendations to the governor.

Asked whether such benchmarks should be made public, he said, “I think it’d be a smart thing to do,” not just for West Virginians wondering how their state is making decisions but for other states as well.

“Eventually, we should be learning from each other,” Marsh said. “This next phase — of reopening — is much more difficult and much more dangerous.”