Epidemiological and virological factors determining dengue transmission in Sri Lanka during the COVID-19 pandemic (preprint)

Background: With the onset of the COVID-19 pandemic in early 2020 there was a drastic reduction in the number of dengue cases in Sri Lanka, with an increase towards the end of 2021. We sought to study the contribution of virological factors, human mobility, school closure and mosquito factors in affecting these changes in dengue transmission in Sri Lanka during this time. Methods and findings: To understand the reasons for the differences in the dengue case numbers in 2020 to 2021 compared to previous years, we determined the association between the case numbers in Colombo (which has continuously reported the highest number of cases) with school closures, stringency index, changes in dengue virus (DENV) serotypes and vector densities. There was a 79.4% drop in dengue cases from 2019 to 2020 in Colombo. A significant negative correlation was seen with the number of cases and school closures (Spearmans r=-0.4732, p=<0.0001) and a negative correlation, which was not significant, between the stringency index and case numbers (Spearmans r= -0.3755 p=0.0587). There was no change in the circulating DENV serotypes with DENV2 remaining the most prevalent serotype by early 2022 (65%), similar to the frequencies observed by end of 2019. The Aedes aegypti premise and container indices showed positive but insignificant correlations with dengue case numbers (Spearman r= 0.8827, p=0.93). Conclusions: Lockdown measures, especially school closures seemed to have had a significant impact on the number of dengue cases, while the vector indices had a limited effect.

Antibody and T-cell responses to a single dose of the AZD1222/Covishield vaccine in previously SARS-CoV-2 infected and naive health care workers in Sri Lanka (preprint)

BackgroundIn order to determine the immunogenicity of a single dose of the AZD1222/Covishield vaccine in a real-world situation, we assessed the immunogenicity, in a large cohort of health care workers in Sri Lanka. MethodsSARS-CoV-2 antibodies was carried out in 607 naive and 26 previously infected health care workers (HCWs) 28 to 32 days following a single dose of the vaccine. Haemagglutination test (HAT) for antibodies to the receptor binding domain (RBD) of the wild type virus, B.1.1.7, B.1.351 and the surrogate neutralization assay (sVNT) was carried out in 69 naive and 26 previously infected individuals. Spike protein (pools S1 and S2) specific T cell responses were measured by ex vivo ELISpot IFN{gamma} assays in 76 individuals. Results92.9% of previously naive HCWs seroconverted to a single dose of the vaccine, irrespective of age and gender; and ACE2 blocking antibodies were detected in 67/69 (97.1%) previously naive vaccine recipients. Although high levels of antibodies were found to the RBD of the wild type virus, the titres for B.1.1.7 and B.1.351 were lower in previously naive HCWs. Ex vivo T cell responses were observed to S1 in 63.9% HCWs and S2 in 31.9%. The ACE2 blocking titres measured by the sVNT significantly increased (p<0.0001) from a median of 54.1 to 97.9 % of inhibition, in previously infected HCWs and antibodies to the RBD for the variants B.1.1.7 and B.1.351 also significantly increased. Discussiona single dose of the AZD1222/Covishield vaccine was shown to be highly immunogenic in previously naive individuals inducing antibody levels greater than following natural infection. In infected individuals, a single dose induced very high levels of ACE2 blocking antibodies and antibodies to RBDs of SARS-CoV-2 variants of concern. FundingWe are grateful to the World Health Organization, UK Medical Research Council and the Foreign and Commonwealth Office.

COVID-19 Case Prediction and Outbreak Control of Navy Cluster in Sri Lanka: Effectiveness of SIR Model (preprint)

Introduction: Infectious diseases such as coronavirus disease 2019 (COVID-19) can spread contagiously fast in semi-confined places, which demand prompt public health interventions such as isolation and quarantine for their effective control. An outbreak of COVID-19 was reported within a cluster of Navy personnel in the Western Province of Sri Lanka commencing from 22nd April 2020. In response, an aggressive outbreak management program was launched by the Epidemiology Unit of the Ministry of Health supported by the Sri Lanka Navy. The objective of this research was to predict possible number of cases within the susceptible population in Sri Lanka Navy. Methods: COVID-19 Hospital Impact Model for Epidemics (CHIME) developed by Predictive Health Care Team at Penn Medicine, Philadelphia, USA, which was a Susceptibility, Infected and Removed (SIR) model was used. The model was run on 20.05.2020 for a susceptible population of 10400, with number of hospitalized patients on the day of running the model being 357, first case hospitalized on 22.04.2020 and social distancing being implemented on 26.04.2020. Social distancing scenarios of 0, 25, 50 and 74% were run with 10 days of infectious period and 30 days of projection period. Results: With increasing social distancing measures, the peak number of infected persons decreased, and the duration of the curve extended. With increasing social distancing from 0% to 74%, the date on which the peak number of infected cases was reported increased from 49th day to the 54th day, the doubling time increased from 3.1 days to 4.1 days, the Ro decreased from 3.54 to 2.83, and expected daily growth rate decreased from 25.38% to 18.53%. The number of COVID-19 cases prevented as per the model ranged from 2.3 – 21.1 %, compared to the base line prediction of no social distancing. When comparing the observed number of cases with the baseline model with no social distancing, a 90.3% reduction was observed.  Conclusion: The research demonstrated the practical use of a prediction model made readily available through an online open-source platform for the operational aspects of controlling outbreaks such as COVID-19 in a closed community. Predictive modelling is a useful tool for outbreak management. 

Epidemiological Characteristics of COVID-19 and Efforts to Prevent Community Transmission: The Sri Lankan Experience (preprint)

Background – With the onset of COVID-19 pandemic, the government of Sri Lanka took proactive measures to prevent a community outbreak in the country. This paper describes the measures taken by the government in the initial stages to contain the virus, along with the epidemiological characteristics of the first 200 laboratory confirmed COVID-19 patients.Methods – Telephone interviews were conducted for first 200 consecutive patients diagnosed with COVID-19, after obtaining informed verbal consent. Descriptive data are presented as binary variables and in frequency distribution tables.Results- From the diagnosis of the first patient, 76 days elapsed for the first 200 patients to be diagnosed. Majority were males in the 40-49 age group. There were three foreign nationals, while others were Sri Lankans. Among the Sri Lankans, 81 (41.1%) had an overseas travel history. Following implementation of the cohort quarantine concept, 47% of the overseas returnees were reported from quarantine centres. Over two-thirds of the patients presented with symptoms (n=137, 68.5%) and the most common symptoms were fever, cough and sore throat. The case fatality rate for the sample was 3.5%. out of the 200 patients, 103 (51.5%) were primary patients, while 92 (46%) were secondary patients. The source of exposure could not be determined for five patients. Conclusions – Due to measures instigated by the government, such as cohort quarantining, extensive contact tracing and testing of close contacts, Sri Lanka was able to prevent a wide spread community outbreak of COVID-19.