The coronavirus disease 2019 (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first emerged in Wuhan, China, in December 2019. It has since spread to 192 countries and territories, infecting over 100 million individuals and claiming over 2.2 million lives. To date, Japan has reported 391,945 cases and 5,833 deaths.
A team of researchers in Japan have developed commercially available antibody tests to estimate the seroprevalence of SARS-CoV-2 infection in a population. Given the importance of this in pandemic management policies, cost-effective and efficient seroprevalence testing methods can help manage local and nationwide outbreaks.
The study, published in the U.S. Centers for Disease Control and Prevention (CDC)’s Emerging Infectious Diseases journal, showed that using reliable antibody tests in conjunction is an effective way to estimate seroprevalence in low prevalence settings. Japan has low seroprevalence, showing the country’s success in preventing the spread of the virus.
The study
The study highlights the importance of antibody testing in countries affected by the coronavirus pandemic. Since many COVID-19-positive individuals may have no symptoms at all, some people may have been infected without realizing it.
Antibody testing can help the government and public health authorities determine the extent of the pandemic in a certain region or country. This can help formulate policies and health measures to prevent another bout of infection.
Countries with low seroprevalence are at a higher risk of a second wave of infection, as this lack of herd immunity allows transmission chains to proliferate.
The researchers used two commercially available antibody tests to detect the SARS-CoV-2 nucleocapsid antigen, including Abbott’s SARS-CoV-2 IgG immunoassay, a chemiluminescent microparticle immunoassay, and Hoffman-La Roche’s Elecsys Anti-SARS-CoV-2 immunoassay, an electrochemiluminescence immunoassay.
To arrive at the study findings, the team conducted a seroprevalence survey of COVID-19 illness in three prefectures of Japan between June 1 and 7, 2020. The researchers chose two prefectures with a relatively high incidence of COVID-19 cases from May 31, 2020. These include Tokyo and Osaka. To compare the findings, the team also selected a prefecture with a low incidence, which is Miyagi, Japan.
All the eligible participants in each prefecture were more than 20 years old and presented with no symptoms of SARS-CoV-2 infection. They completed a questionnaire before the collection of blood samples by trained healthcare professionals. From there, the researchers collected serum and tested these samples using the two antibody tests.
The samples that were positive or borderline negative were sent to Japan’s National Institute of Infectious Diseases for a neutralizing antibody assay with VeroE6 or TMPRSS2 cells.
What the study found
Overall, 13,547 people were invited to participate in the study. However, only 7,950 approved to participate. Of these, eight people were seropositive in both, which means they contracted SARS-CoV-2 in the past and developed antibodies against it. However, 30 samples tested positive by only one test, 15 each for Abbott and Roche tests.
Despite some testing positive for just one test, only eight samples that were positive for both commercial tests also tested positive for the neutralizing antibody assay. The study findings demonstrated that two positive test results accurately identified seropositive participants.
The team concluded that the two commercial tests with high sensitivity and specificity would be appropriate to use to determine the extent of the pandemic in a particular region.
We estimate that SARS-CoV-2 seroprevalence ranged from 0.03%–0.17% in Japan in early June 2020. Public health officials in low prevalence areas should consider using 2 antibody tests in conjunction for accurate surveillance.”
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