No abstract

As a response to the coronavirus disease 2019 (COVID-19) pandemic, Vietnam enforced strict quarantine, contact tracing and physical distancing policies resulting in one of the lowest numbers of individuals infected with severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) globally. This study aimed to determine the prevalence of SARS-CoV-2 antibody positivity among high-risk populations in Vietnam. A prevalence survey was undertaken within four communities in Vietnam, where at least two COVID-19 cases had been confirmed. Participants were classified according to the location of exposure: household contacts, close contacts, community members, and healthcare workers (HCWs) responsible for treating COVID-19 cases. Participants completed a baseline questionnaire and SARS-CoV-2 IgG antibodies were quantified using a commercial assay. A total of 3049 community members and 149 health care workers consented to the study. Among 13 individuals who were seropositive (0.4%), five household contacts (5/27, 18.5%), one close contact (1/53, 1.9%), and seven community members (7/2954, 0.2%) had detectable SARS-CoV-2 antibodies. All HCWs were negative for SARS-CoV-2 antibodies. Participants were tested a median of 15.1 (interquartile range from 14.9 to 15.2) weeks after exposure. Our study found a low prevalence of SARS-CoV-2 antibodies in high-risk communities and healthcare workers in communities in Vietnam with known COVID-19 cases.

BackgroundAntibodies are critical responses to protect the host from dengue virus(DENV) infection. Antibodies target DENV by two pathologic mechanisms: virus neutralization and infection enhancement. In dengue patients, the absence of neutralizing activity in the presence of FcγR implies that infection-enhancing activity hampers the neutralizing activity of antibodies, which could potentially lead to symptomatic presentations and severe clinical outcomes.MethodsA total of 100 pair serum samples from adult healthy volunteers were obtained during the dengue season in Ha Noi in 2015 for evaluation of neutralizing and infection-enhancing activity. Additionally, 20 serum samples from acute secondary DENV infection patients were also used as the patient group in this study. PRNT was performed on BHK cells and FcγR-expressing BHK cell lines for all serum samples.ResultsOut of 100 residents, positive neutralizing antibodies (N.A) were found in 44.23 and 76.92% for DENV-1; 38.46 and 75% for DENV-2; 19.23 and 15.38% for DENV-3; and 1.92 and 9.62% for DENV-4 for pre and post-dengue season respectively. The percentage of post-exposure residents having positive responses against single, two, or more than three DENV serotypes were 38.46, 44.23 and 15.38%, respectively. A total of 34 residents were DENV seropositive before the dengue season and these individuals demonstrated further elevation of IgG antibodies after the dengue season. At the end of the season, 18 residents were confirmed to be new asymptomatic DENV infection cases. In both groups, N.A titers determined on BHK cells were higher than that on FcγR-expressing BHK cells. In heterotypic N.A responses, N.A titers to the infecting serotype from the samples obtained from pre-exposure group were significantly higher than those of the patient group. However, fold enhancement to the infecting serotypes from the samples in the pre-exposure group was substantially lower as compared to that of the patient group.ConclusionBefore and after the dengue season, serum samples from healthy volunteers demonstrated high levels of neutralizing antibodies and low or absence of infection-enhancement activity. The results suggest that while infection-enhancement activity hampers neutralizing activity of antibodies, high levels of DENV neutralizing antibodies set a critical threshold in facilitating the prevention of disease progression.Electronic supplementary materialThe online version of this article (10.1186/s12879-017-2894-7) contains supplementary material, which is available to authorized users.

Aims: Our study aimed to determine neutralization antibodies against measles virus and some related factors in women of childbearing-age from 18 to 30 years old, in Hanoi, Vietnam. Methodology: In 2018, a cross-sectional study was conducted on 1,235 childbearing-age women from 18-30 years old in Bavi district, Hanoi, Vietnam. The study participants were interviewed by using a structured questionnaire which included demographic information, and history of measles. The measles neutralization antibodies (MNA) of these participants were quantified by a plaque reduction neutralization test (PRNT). The data were analyzed using the Epidata 3.1 and Stata 14.2 software. Results: The results showed that only 58.5% had MNA at sufficient protective levels (≥120mIU/ml), up to 12.5% were negative for MNA, and 358 women (29%) had MNA at insufficient protective levels. In addition, we found that the participants’ working as public employees, having two children, and being ≥ 25 years of age were all positively associated with the sufficient protective antibody levels (P<0.05). A weak positive correlation between age and MNA titers was determined (r= 0.26). Conclusion: Approximately half (41.5%) of the women of childbearing age in this study did not have sufficient protective antibodies against measles virus. The study results suggest that it is necessary to boost measles vaccine to prevent the sporadic measles infection in women of childbearing age in Hanoi and to quantify the dynamics of maternal measles antibody levels in infants born from these women, so as to provide evidences to control measles incidence in children up to 9 months of age in the future.

No abstract

No abstract