Thu, Dec 17, 2020 page3

• CECC downplays results of blood test study

  • By Lee I-chia / Staff reporter
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  The Central Epidemic Command Center (CECC) yesterday downplayed a study earlier this year by Taipei Veterans General Hospital that suggested about 11,800 adults in Taiwan might have contracted the virus that causes COVID-19, based on a seroprevalence rate of antibodies to SARS-CoV-2 of 0.05 percent.

  The center said the study, which was published in the international medical journal Lancet Regional Health — Western Pacific in October, cannot reflect the general population.

  The study’s researchers used residual specimens from blood tests administered to 14,765 adults that visited the hospital’s outpatient and emergency departments over two periods — May 25 to 30 and July 6 to 8 — and screened them for anti-SARS-CoV-2 antibodies.

  Seven of the specimens collected in May and four collected in July tested positive for the antibody, and the unweighted seroprevalence was approximately 0.07 percent.

  However, as about 78.2 percent of people whose specimens were used in the study were older than 50, the researchers weighted the prevalence by age, resulting in an overall weighted seroprevalence of 0.05 percent.

  That 0.05 percent rate implies that about 11,800 adults in Taiwan might have anti-SARS-CoV-2 antibodies, which is about 24 times the number of confirmed cases reported as of Sept. 2, the article said.

  The authors wrote that “a large proportion of Taiwanese people might have been infected with SARS-CoV-2 virus, however, most of them were asymptomatic or mildly symptomatic and not qualified for a diagnostic viral nucleic acid test.”

  Their journal article said the seroprevalence of 0.05 percent in Taiwan is significantly lower than most nations in the world, and that the detection rate did not increase in about a week after a four-day long holiday (the June 25 to 28 Dragon Boat Festival), in which many people took part in social activities, indicating that Taiwan’s disease prevention measures were effective.

  Asked by reporters to comment on the study, Centers for Disease Control (CDC) Deputy Director-General Chuang Jen-hsiang (莊人祥), who is also the CECC spokesperson, said the study used two types of serological assays, which could possibly have prevented cross-reactivity of antibodies against other viruses.

  The study did not identify whether the people whose blood contained antibodies against SARS-CoV-2 had returned to Taiwan from other countries or had been exposed to confirmed cases, so the research findings could not be used to reflect the general population.

  National Taiwan University vice president Chang Shan-chwen (張上淳), convener of the CECC specialist advisory panel, said one of the serological assays used by the study was a commercial assay and the other was developed by an Academia Sinica laboratory, but the sensitivity and specificity of the assays were still up for debate.

  How the people enrolled in the study were selected and whether they could represent the general population was also subject to discussion, as the study did not provide their background information, including whether they had recently returned to Taiwan from abroad.

  “What we can clearly see is the seroprevalence in Taiwan is very low, especially given that the study’s second period of specimen collection was after a long holiday, the seropositive rate did not increase, nor was community spread observed,” Chang said.

  That showed that more discussion was needed as to whether the study could be used to estimate how many people in Taiwan have been infected with the virus.
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