China testing Wuhan residents to find out actual rate of Covid-19 infection, antibodies

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China is carrying out a large-scale “seroprevalence” survey to check for Covid-19 antibodies in the population of Wuhan where the novel coronavirus first emerged late last year before spreading rapidly in three months to trigger a global pandemic.

It was initiated in March under China’s national health commission (NHC), the central ministry coordinating the country’s control and containment measures against the outbreak.

A seroprevalence study is carried out by collecting blood samples from a large population sample across age groups to check for antibodies against particular disease – in this case, Covid-19.

Besides the general population, the “sero” investigation is likely focussing on high-risk groups like those who worked in wet markets in Wuhan, and people who dealt and traded in wildlife.

The result will aid in separating the confirmed and symptomatic cases from the asymptomatic ones or those individuals, who have been infected, do not show any symptom but could infect others.

In simple terms, the survey results will reveal for the first time the total number of Covid-19 infections in Wuhan, and not just the number of the disease cases.

China has so far not made public any information about the study, which could have potentially been done on hundreds of thousands of Wuhan residents, the first epicentre of the pandemic and a city of around 11 million people.

The Chinese Centre for Disease Control and Prevention (CDC) – which works under the NHC – and the office of respiratory expert, Dr. Zhong Nanshan, who heads the top experts’ team advising the government on fighting the outbreak did not respond to HT’s questions on the survey.

HT’s questions were sent out through the information department of China’s cabinet, the State Council.

Wuhan has so far accounted for over 2500 deaths and more than 50000 infections in China’s tally of 81708 confirmed cases and 3331 deaths.

China has only started to share the number of asymptomatic patients in the country from last week.

The WHO is not part of the survey but is aware that it is being conducted, the WHO’s china representative, Gauden Galea, told HT earlier.

“We know that China is now doing a ‘sero’ survey. This is a survey to look at antibodies in the blood of people in Wuhan,” Galea said.

Galea explained both the survey and its importance.

“I distinguish between infection and disease. So, being infected is the process of getting the infection and it taking hold inside the body. And, then it manifests as the disease Covid-19. But the disease is distinct from the infection but when people are infected, their immune system reacts and develops antibodies,” Galea explained.

Why is it important?

“…there’s a big question in the world how many asymptomatic people are there who got infected but don’t (show symptoms)…you hear very many estimates…but seroprevalence survey would give the answer. It would tell you,” Galea said.

In a recent medical paper on Covid-19 titled “Estimating the ascertainment rate of SARS-CoV-2 infection in Wuhan”, an expert on epidemiological surveillance and intervention, Theodore Lytras, from the Athens-based National Public Health Organisation wrote about the importance of seroprevalence surveys.

“That’s the most important conclusion that should be drawn for our study. We urgently need seroprevalence surveys, which involves testing blood from a population sample to find out whether they have antibodies to the coronavirus, and thus how many of them had been infected,” Lytras told media reporters.

Lytras’ and his colleagues’ modelling suggested that most of the population in Wuhan became infected (probably with little to no symptoms), and although the lockdown obviously helped, the outbreak stopped because there were few uninfected people left for the virus to infect.

“This (seroprevalence survey) will give us definite answers about how many people are actually infected with the coronavirus. Our modelling for Wuhan suggests that nearly every one got infected, but we could be wrong. Only a seroprevalence survey will tell,” Lytras added.

The WHO’s Galea said the results of the survey – when published – will be avidly followed by governments, researchers and planners all around the world.

“This (China) is the first country that has experienced a wave of community transmission, at least in Wuhan. Therefore (the seroprevalence survey) will give you the shape of the infection curve, and not just the disease curve, which is what we have been able to see up to now,” Galea said.