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Wuhan tests show coronavirus herd immunity is a long way off
Authorities in the coronavirus pandemic’s original epicenter have started testing for antibodies among thousands of people returning to work, and others without symptoms, to gain a clearer picture of immunity levels in the city and try to prevent a second wave of disease.

There is good and bad news in the initial results—for Wuhan and for other hard-hit places around the world.

The good news is that the proportion of people with antibodies is considerably higher than that of confirmed cases, suggesting many people here were infected without realizing it, developed mild or no symptoms, and could now be immune.

The bad news is that the number of those with antibodies still falls far short of “herd immunity”—levels above 50% typically needed for the virus to die out. And there could still be thousands of unidentified asymptomatic cases in the city of 11 million, the results suggest.

Wuhan’s Zhongnan Hospital found that 2.4% of its employees and 2% to 3% of recent patients and other visitors, including people tested before returning to work, had developed antibodies, according to senior doctors there.

Quote:“This is a long way from herd immunity,” said Wang Xinghuan, the head of Zhongnan hospital, one of the city’s largest. “So a vaccine may be our last hope.”

Until a vaccine is developed, he and other doctors warned, many social-distancing and other restrictions would have to remain in place in Wuhan, even though a 76-day lockdown technically came to an end last Wednesday.

Doctors and public-health experts cautioned that the results are preliminary and based on relatively small samples.

Still, they offer an early indicator of what might await other hard-hit places, including New York City, that are trying to strike a balance between easing lockdowns and triggering a second wave of infections among residents who remain susceptible to the virus.

The antibody tests check the blood for immune-system markers that indicate a person has been infected by the virus and fought it off. Since the pandemic erupted, authorities in Wuhan have focused on conducting nucleic-acid tests—which are done with a throat swab and indicate current infection—on people with symptoms and those known to have had close contact with confirmed cases.

Public-health experts say wider nucleic acid testing is now required to find asymptomatic cases infected through broader “community spread.” But blood tests for antibodies are also needed, they say, to work out how much of the total population might be immune and how much likely remains susceptible.

Wuhan started to conduct more of both tests as it prepared to relax its lockdown last Wednesday, when it began allowing many residents to leave or to go back to work, as long as they could prove they were healthy.

Nucleic-acid tests are now mandatory for anyone leaving the city, and while they aren’t compulsory for those returning to work, many companies are demanding them. Some employers also require antibody tests. Several hospitals have started doing both for all patients and staff.

This week, the city launched a new initiative to test 11,000 residents—including security guards and taxi drivers—for antibodies by next Wednesday, according to official media outlets.

Similar antibody testing will also be done in nine other provinces and large cities, including Beijing and Shanghai, those state media reports said. National and Wuhan health authorities didn’t respond to requests for comment.

The antibody tests at Zhongnan Hospital involved 3,600 healthy employees, including security guards and cleaners as well as doctors and nurses. They also included about 5,000 visitors, including people who were required to take the tests before being allowed to return to work or leave Wuhan.

Only two of the hospital workers were found to still be infected with the virus, and both were asymptomatic, Dr. Wang said.

The results showing more than 2% of both groups had antibodies suggests the virus might have spread much further than indicated by China’s official figures: Wuhan accounts for 50,008 confirmed cases, or about 0.45% of its population, according to the local government.

It’s striking that antibody results were roughly the same for hospital visitors and staff, given that staff are more likely to have encountered the virus. One explanation could be that hospital staff had more exposure to the virus but also more protective gear, said Robert Garry, a virologist at Tulane University in New Orleans.

Several experts warned that further data and research were needed to establish a clear picture of how many people in the city had antibodies. They also said that it was unclear what level of immunity such antibodies would provide.

Quote:“It is not safe to assume if one has a positive antibody test, one is immune and can go back to work,” said Lin Xihong, a professor of biostatistics at the Harvard T.H. Chan School of Public Health.

Doctors in Wuhan have reported several cases in which people who became sick with the virus recovered and tested negative, only to test positive again later. While some suspect that may be due to flawed test results, others remain concerned about the potential for reinfection.

Asymptomatic cases are also still a worry for many doctors in Wuhan, although some say they are less infectious than those with symptoms.

Since lifting the lockdown, Wuhan has announced no new confirmed cases—defined as people who test positive and have symptoms. But it has revealed dozens of asymptomatic cases, defined as people who test positive but show no symptoms.

Of 143,056 people tested before going back to work between March 29 and April 10, the local government says that 113—or 0.08%—were found to be still carrying the virus. Almost all of them were asymptomatic.

Quote:“One thing that means is that even in a place where the virus has gone through and they’ve come down the other side of the curve, there are going to be new cases popping up,” said Dr. Garry,of Tulane University.

Quote:The proportion of such cases among people returning to work so far was low, said Zhongnan hospital’s Dr. Wang. But as more people resume their jobs, “there’s still a risk of another outbreak,” he said.

“We still lack an understanding of how many asymptomatic cases there actually are.”


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