Study: Wuhan SARS-CoV-2 Antibody Seroprevalence Less Than 7%

March 19, 2021
Kevin Kunzmann

Regardless of symptom status, the rate of participants positive for pan-immunoglobulins with neutralizing antibodies at baseline remained stable throughout 2020.

New seroprevalence data from the COVID-19 outbreak epicenter of the world shows SARS-CoV-2 antibodies were prevalent in fewer than 7% of its population.

The Wuhan, China-based cross-sectional data, which observed nearly 10,000 individuals in the area from the initial COVID-19 outbreak to early December 2020, emphasized the need for effective mass vaccination strategies in lieu of reduced confidence in antibody prevalence among originally exposed persons.

Investigators from the Wuhan Center for Disease Control & Prevention and the Peking Union Medical College in Beijing conducted the longitudinal assessment to observe the seroprevalence and kinetics of anti-SARS-CoV-2 antibodies at Wuhan’s population level. As they noted, nearly 60% of confirmed mainland China cases originated in Wuhan, despite rapid containment attempts of the virus in the region from late January through early April 2020.

“With the spreading of COVID-19 to other countries, the declaration of a global pandemic, and the development of vaccines, assessing the proportion of the population that have been infected and who are immune is of utmost importance for determining effective prevention and control strategies to reduce the likelihood of future resurgence of the pandemic,” investigators wrote.

The team conducted its multi-stage, cluster random sampling assessment with 100 systematically-selected communities from Wuhan’s 13 districts. Family members from selected communities were invited to participate at their community health centers, with eligible individuals being those who lived in Wuhan for ≥14 days since December 1, 2019.

Volunteer participants completed standardized electronic questionnaires including demographic and clinic questions, as well as self-reported symptoms associated with COVID-19, or any previous COVID-19 diagnosis.

Participants also gave venous blood samples for immunological testing on April 14-15, 2020—after the end of the regional lockdown. Investigators analyzed blood samples for pan-immunoglobulins, IgM, IgA, and IgG antibodies against SARS-CoV-2 nucleocapsid protein and neutralizing antibodies.

Another 2 successive follow-ups occurred between June 11-13, then October 9 – December 2020, including more blood samples.

The observed population included 4600 randomly-selected households. Among them, 3599 families with 9702 individuals attended the baseline visit. Of those, 9542 individuals had sufficient samples for the analysis.

Investigators observed that 532 (5.6%) participants were positive for pan-immunoglobulins against SARS-CoV-2. Baseline adjusted seroprevalence was just 6.92% (95% CI, 6.41 – 7.43) in the population.

Among pan-immunoglobulin-positive patients, 437 (82.1%) were asymptomatic. Another 69 (13%) were positive for IgM antibodies; 84 (15.8%) were positive for IgA antibodies; 212 (39.8%) were positive for neutralizing antibodies at baseline. All patients (n = 532) were positive for IgG antibodies.

The rate of participants positive for pan-immunoglobulins with neutralizing antibodies at baseline remained stable for the June (44.6%) and October – December (41.2%) follow-ups.

Among the 335 individuals who attended all 3 follow-up visits and remained positive for pan-immunoglobulins, neutralizing antibody levels did not significantly decrease over the trial period. That said, neutralizing antibody titers observed in asymptomatic individuals were lower than in the confirmed COVID-19 cases and symptomatic individuals.

“Among those with available data, the proportions of participants who were positive for IgG and neutralizing antibodies and the concentrations of neutralizing antibodies were relatively stable for at least 9 months across the study period, regardless of whether the individuals were symptomatic or not,” investigators wrote. “Individuals who were positive for antibodies against SARS-CoV-2 tended to be clustered in family groups.”

Given the low estimated seroprevalence in Wuhan, the original COVID-19 epicenter, the investigators concluded that vaccination will be necessary to achieve herd immunity.

“The proportions of participants who were positive for IgG and neutralizing antibodies were stable for at least 9 months after exposure, regardless of whether individuals were asymptomatic, which indicates that passive and active immune strategies could be considered to protect the at-risk population from severe infection or reinfection,” they wrote.