Sero-Prevalence of Covid-19 among workers in Malaysia

From the beginning of the pandemic in Feb 2020, Malaysia has been through 4 waves of outbreak, the magnitude of each wave is several orders larger than the preceding one. By the end of the fourth wave in October 2021, Malaysia has among the highest death toll in Asia, cumulative incidence of confirmed cases has reached 7.0% (>30% in Klang Valley). However it remains uncertain what is the true proportion of the population infected. We conducted a sero-survey on 1078 workers from 17 worksites in Klang Valley and Perak between July and September 2021. We tested them for SARS-CoV-2-specific antibodies using Ecotest, a lateral flow immunoassay (LFIA). The ability of antibody testing to detect prior infection depends on the assay and sero-reversion. We therefore adjusted the prevalence estimates to correct for potential misclassification bias due to the use of LFIA and sero-reversion using test sensitivity and specificity results estimated from an independent validation study. The mean age of the workers was 32 years, 89% were male and migrant workers comprised 81% of all subjects, 59% the subjects were from Klang valley. 33% of workers had prior RT-PCR confirmed Covid-19 infections. We estimated 82.2 percent of workers had been infected by Covid-19 by July-September 2021. Prevalence was 99.9% among migrant workers and 12.1% among local workers. Klang Valley, the most industrialized region in Malaysia where most migrant workers are found, had 100% prevalence, giving an infection-to-case ratio (ICF) of [~]3. Our sero-prevalence results show that the incidence of Covid19 is extremely high among migrant workers in Malaysia, consistent with findings from other countries such as Kuwait and Singapore which also hosted large number of migrant workers.