Low seroprevalence of COVID-19 in Lao PDR, late 2020

Abstract

Background In 2020 Lao PDR had low reported COVID-19 cases but it was unclear whether this masked silent transmission. A seroprevalence study was done August - September 2020 to determine SARS-CoV-2 exposure. Methods Participants were from the general community (n=2433) or healthcare workers (n=666) in five provinces and bat/wildlife contacts (n=74) were from Vientiane province. ELISAs detected anti- SARS-CoV-2 Nucleoprotein (N; n=3173 tested) and Spike (S; n=1417 tested) antibodies. Double-positive samples were checked by IgM/IgG rapid tests. Controls were confirmed COVID-19 cases (n=15) and pre-COVID-19 samples (n=265). Seroprevalence for the general community was weighted to account for complex survey sample design, age and sex. Findings In pre-COVID-19 samples, 5·3%, [95% CI=3·1-8·7%] were anti-N antibody single-positive and 1·1% [0·3-3·5%] were anti-S antibody single positive. None were double positive. Anti-N and anti-S antibodies were detected in 5·2% [4·2-6·5%] and 2·1% [1·1-3·9%] of the general community, 2·0% [1·1-3·3%] and 1·4% [0·5-3·7%] of healthcare workers and 20·3% [12·6-31·0%] and 6·8% [2·8-15·3%] of bat/wildlife contacts. 0·1% [0·02-0·3%] were double positive for anti-N and anti-S antibodies (rapid test negative). Interpretation We find no evidence for significant SARS-CoV-2 circulation in Lao PDR before September 2020. This likely results from early decisive measures taken by the government, social behavior, and low population density. High anti-N /low anti-S seroprevalence in bat/wildlife contacts may indicate exposure to cross-reactive animal coronaviruses with threat of emerging novel viruses. Funding Agence Française de Développement. Additional; Institut Pasteur du Laos, Institute Pasteur, Paris and Luxembourg Ministry of Foreign and European Affairs (“PaReCIDS II”).

The Pandemic Experience in Southeast Asia: Interface Between SARS-CoV-2, Malaria, and Dengue

“…The true scale of the problem may have been underestimated in several countries due to case under-reporting related to poor testing infrastructure (11) and civil unrest (12). Even so, a few serosurveys conducted during the second half of 2020 demonstrated relative population naivety (13,14). While the Western world was swept by devastating case numbers and fatalities, SEA seemed to emerge from the 2020 pandemic year relatively unscathed.…”

A strategy to assess spillover risk of bat SARS-related coronaviruses in Southeast Asia

“…The authors also tested serum samples collected during the pandemic (August–September 2020) and detected antibodies in 5.2% (anti-N) and 2.1% (anti-S) of the general public, and in 20.3% (anti-N) and 6.8% (anti-S) of bat/wildlife contacts (bat guano collectors, wildlife animal vendors, and family members of bat contacts, catchers or guano collectors). The authors noted that high seroprevalence may also reflect the frequent trade in bush meat and low biosafety awareness reported in earlier surveys in Lao PDR 60 , 65 .…”

“…We believe we are justified in using non-CoV data in our analyses for several reasons. First, there are very few pre-COVID human serosurveys that specifically tested for SARSr-CoV exposure 17 , 60 , and we wanted to parameterize our spillover estimate with a wide range of possible values for infection and seroconversion using other RNA viruses that are known or likely able to be transmitted via direct exposure to bats or bat excreta. We acknowledge that there may be substantial variation in the ability of different SARSr-CoVs or other bat-harbored viruses to cause infection and seroconversion in humans; however, we know little about the large diversity of viral strains circulating in bat populations and the host cellular and immunological factors that could influence seroconversion after exposure for most viruses 61 .…”

“…Data from serological analysis also demonstrates high seroprevalence in Lao PDR. Specifically, Virachith and colleagues detected SARS-CoV-2-specific anti-N and anti-S antibodies in 5.3% and 1.1%, respectively, of human serum samples collected in 2018 (i.e., pre-COVID-19) in Lao PDR 60 . The authors also tested serum samples collected during the pandemic (August–September 2020) and detected antibodies in 5.2% (anti-N) and 2.1% (anti-S) of the general public, and in 20.3% (anti-N) and 6.8% (anti-S) of bat/wildlife contacts (bat guano collectors, wildlife animal vendors, and family members of bat contacts, catchers or guano collectors).…”

Covid-19: What went wrong after initial success in Laos?

“…In a study published in the Lancet , researchers estimated that there were just 4640 excess deaths in Laos between January 2020 and December 2021, fewer than any other country bordering China except for Bhutan and North Korea 1. A survey of antibody prevalence2 in five provinces suggested there was no widespread transmission of SARS-CoV-2 up to September 2020,3 while only 49 confirmed cases were confirmed as of 10 April 2021.…”