While China has lifted a more than two-month coronavirus lockdown in the city of Wuhan, testing is still too behind to know for sure when restrictions should be lifted in the United States, Harvard epidemiologist Marc Lipsitch told the USA TODAY Editorial Board on Wednesday.

Even when officials relax social distancing measures – allowing students return to school and workers to their jobs – the U.S. may see a second wave of cases, he said.

“If we relax restrictions ... there’s every reason to expect a resurgence of cases and we’re back in the same problem,” Lipsitch said.

Lipsitch, an expert in public health interventions, told the Editorial Board he believes a large portion of the population must be immune to the virus either through infection or vaccinations before the country can be reopened.

Only three states – New York, Louisiana and Washington – have matched or exceeded the testing rate of South Korea, whose testing procedures experts hold out as a model for the world. The country has performed 431,734 tests, according to the Korea Centers for Disease Control and Prevention, which is about 1 out of every 119 people.

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In comparison, Vice President Mike Pence said last week that more than 1.2 million tests have been given, which means roughly 1 in every 273 people were tested given that the U.S. population is at about 327 million.

However, Lipsitch suspects testing numbers are only a fraction of actual cases in the U.S.

The uneven testing rate among states has left public health and medical professionals without a clear picture of how much the coronavirus is spreading: Some states are not consistently reporting negative results, the U.S. Food and Drug Administration was slow to approve private sector testing. The lack of capacity has limited testing.

The country's future rests in its ability to test and its immunity to the virus, either through infection or vaccinations, Lipsitch said, which could take up to a year to develop and be distributed.

Earlier this month, the FDA authorized the first test for the coronavirus that measures antibodies in the blood. Such tests could identify people who have recovered from COVID-19, key for knowing who’s immune and for developing a vaccine.

However, a study from China suggests that patients who recover from COVID-19 may have a higher risk of reinfection than experts previously suspected. After analyzing the blood samples of 175 patients discharged from the Shanghai Public Health Clinical Center, researchers from Fudan University found that nearly a third had unexpectedly low levels of antibodies.

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In the meantime, Lipsitch doesn’t believe that anyone will have answers on when social distancing measures can be lifted at least for another month or two. Although he acknowledged that the decision is also partly economic, and not totally scientific, he warned places that prematurely reopen may ultimately “see the consequences” of their actions.

As the U.S. surpassed 400,000 cases and 14,000 deaths on Wednesday, Lipsitch called COVID-19 “the big one” – the largest pandemic that the world has seen since the Spanish Flu in 1918.

Studies suggest social distancing measures had worked against the 1918 epidemic until they were hastily lifted by some cities, like Denver, in early celebrations. Instead of continuing to “flatten the curve,” these cities experienced a second spike in cases.

“A lot of the confusion, in general, is premised on the misunderstanding that if you control the epidemic once, then you’re done,” Lipsitch said. “There’s no reason to think that.”

Contributing: Elizabeth Weise, Matt Wynn and Kevin Crowe, USA TODAY. Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.