Highlights Serum IgG antibody responses developed in 95% of mildly symptomatic individuals by day 14 and all subjects had seroconverted by day 30. Serum IgM and IgA antibody responses were lower and less frequent than corresponding IgG responses, and peaked and declined earlier 100% of mild symptomatic individuals developed an IgG antibody response by day 30. Fewer than 45% of asymptomatic infected individuals had seroconverted by day 30 post-PCR diagnosis. Impact on modeling of herd immunity.

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Background: In December 2019, the COVID-19 pandemic began in Wuhan and quickly spread in China and other countries in the world. The SARS-CoV-2 virus reached Bangladesh in March 2020 and the index case of the first cluster of COVID-19 was reported on 13 March, 2020, in Madaripur District. Methods: A team from the Institute of Epidemiology, Disease Control and Research (IEDCR), of Ministry of Health and Family Welfare, Bangladesh investigated the cluster, established active syndromic surveillance for respiratory diseases, and implemented control activities. Results: The index case traveled from Italy to Bangladesh and developed respiratory symptoms and sought medical treatment in Dhaka. He was diagnosed with COVID-19 and transferred and isolated in a hospital on the day of diagnosis. We followed up his contacts as soon as we got their names and contact information. We quarantined 34 among 139 contacts, rest of them were missed contacts. The attack rate among the index cases’ contacts was 18% (6/34). Eight cases in Madaripur District with COVID-19 were epidemiologically linked to the index case. The most common symptoms were fever (100%) and cough (86%). One case was asymptomatic. The Bangladesh influenza pandemic containment plan was modified for COVID-19 mitigation which included establishing a containment zone, mobilizing the local administrative authorities, and obtaining support from local community, religious and political leaders. Active case search in the containment zone identified new cases. No new cases were linked with the nine COVID-19 cases. Conclusion: Active surveillance by health authority, prompt isolation of cases, quarantine of contacts and establishing a containment zone to focus mitigation efforts supported the prevention efforts for further transmission of the virus from this first COVID-19 cluster in Bangladesh.