Seroprevalence studies directly measure antibodies, acquired by natural infection or vaccination, at a population level, providing a profile of humoral immunity. They provide information on subclinical or under-reported infections that may have been missed by routine diagnostic testing and are interpreted in conjunction with routine data sources such as COVID-19 case notifications and vaccine coverage. Therefore, seroprevalence studies assist efforts related to understanding the epidemiology of COVID-19 that is essential to control the pandemic and mitigate its impact. These efforts require combining data from different sources including COVID-19 specific seroprevalence studies and multi-source surveillance systems.
COVID-19 specific seroprevalence studies entail testing a representative sample of a population for the presence of SARS-CoV-2 antibodies. These are designed as one-time or repeat cross-sectional or prospective cohort studies that can be used to understand infection in specific population groups (e.g. health care workers, at-risk patient groups), and to collect useful ancillary data, such as vaccine coverage, risk or preventive behaviours, morbidity and mortality.
Seroprevalence data that emerges has the potential to inform implementation of infection prevention and control interventions, public health and social measures (PHSM) and vaccination. This data can be interpreted while accounting for current knowledge of SARS-CoV-2 humoral and cellular immunity, antibody types being detected, antibody waning, performance of serological assays, population represented and design and quality of the overall study. By comparing seroprevalence between different groups (e.g. age, sex, geography, etc.) it is possible to identify susceptible sub-populations that may require a review of PHSM or targeting of vaccination programmes and Interpret these SARS-CoV-2 seroprevalence between different groups for effective public health decision-making.
Providing support to Myanmar country office
The WHO UNITY protocols provide a standardized and timely international investigation framework for conducting COVID-19 specific seroprevalence studies in Member States. Currently, Myanmar is involved in developing a study methodology in line with the WHO’s Unity protocol. It sought WHO’s three level assistance between the Unity desk of WHO HQ, SEARO team and WHO country office of Myanmar to develop a sound study methodology for conducting a COVID-19 specific seroprevalence survey in the country and seek other related technical assistance.
The decision to undertake such a survey was taken during the second wave of the transmission of the Delta variant of SARS-CoV-2 virus with a view to providing valuable inputs in the development of the vaccination strategy in the country. It was anticipated that this strategy would help the country in estimating the current level of seroprevalence that is emerging due to naturally acquired or vaccine induced immunity.
The health operations team of the Incident Management Support Team (IMST) together with the research policy and corporation (RPC) unit of the WHO SEA Regional Office facilitated the discussion between the WHO HQ, Regional Office and the WHO’s country office for Myanmar focusing on providing support for developing the study methodology in alignment with WHO’s Unity study protocol for the proposed seroprevalence survey. One key focus area was to achieve a balance between feasibility and operational cost in selecting the study population along with a reasonable sample size to provide valid estimates of the national seroprevalence estimates. The other areas of interest were related to the WHO recommended laboratory diagnostic methods, supplies, and logistics.
The Regional Office provided data collection forms used in seroprevalence studies conducted in other countries. Further, their team gave clear specifications for both tests to be used in seroprevalence studies as per WHO recommendations. HQ team also offered support for calculation of the sample size and sampling technique. Where vaccination programmes are concerned, interpretation of seroprevalence data will depend on the uptake and types of vaccines employed among the population under study. If vaccine uptake in the study population is very low, seropositivity will be mostly attributed to infection. Where vaccine uptake is high, consideration should be given to the type of vaccine deployed in the study population.
A methods paper (Early epidemiological investigations: World Health Organization Unity protocols provide a standardized and timely international investigation framework during the COVID-19 pandemic) prepared by WHO with the involvement of all levels was shared as part of the orientation and discussions. Currently Myanmar country office is involved in the development of the study methodology based on inputs provided.