OBJECTIVE: To assess the magnitude of active and recovering COVID‐19 patients among at‐risk communities and to identify the factors associated with positive serology. METHODS: Four hundred and eighty‐three close contacts of COVID‐19 patients residing in Ho Chi Minh City, Vietnam, during the fourth wave of the COVID‐19 epidemic (September and October 2021) were included. Five weeks after exposure to a COVID‐19 patient, they underwent a serology test using the BIOSYNEX COVID‐19 BSS kit. RESULTS: The median age of participants was 37 years. A total of 34.6% individuals presented at least one clinical symptom between the time of contact with the COVID‐19 patient and inclusion in study. A total of 1.7% unvaccinated individuals tested positive for SARS‐CoV‐2 using real‐time PCR, and 9.5% had evidence of recent infection (positive PCR and/or IgM). A further 26.7% unvaccinated individuals presented evidence of a past infection (positive IgG only). Socio‐demographic characteristics, vaccination status and clinical symptoms were not associated with a positive IgM test. CONCLUSION: This is the first serosurvey conducted during the fourth wave of the epidemic in Vietnam. It revealed a seropositivity rate higher than in previous studies and confirmed the hyperendemicity of SARS‐CoV‐2. Testing using rapid serological tests proved to be a reliable, easy‐to‐use method and enabled a rapid estimation of the burden of COVID‐19.
Seroprevalence of SARS‐CoV‐2 among high‐density communities and hyper‐endemicity of COVID‐19 in Vietnam