Coronavirus disease (COVID-19) technical guidance by WHO Investigation protocol for COVID-19 | Page 5

former are likely to be lower, if they seroconvert at all, than in infected patients exhibiting
symptoms. These are considerations for the interpretation of any COVID-19 virus
seroepidemiological investigation.
2
Study procedures
2.1 Study design
The seroepidemiological investigation for COVID-19 virus infection is a population-based, age-
stratified prospective study. It is intended to provide key epidemiological and serologic
characteristics of COVID-19 virus.
There are three possibilities for how this study can be implemented:
1) Cross-sectional investigation
2) Repeated cross-sectional investigation in the same geographic area (but not necessarily the
same individuals each time)
3) Longitudinal cohort study with serial sampling of the same individuals each time
COMMENT: The first option will likely be the easiest to implement for countries to implement, while
the third provides the most comprehensive information on extent of infection, as described below.
The choice as to how this study will be implemented should be determined by feasibility and
available capacity.
The timing of the study will depend on the specific public health questions that need to be
addressed. If serial sampling is to be conducted, it is best to initiate the investigation as quickly as
possible. Serial sampling can then be conducted as long as possible, as determined by capacity and
resources.
For one-time cross-sectional investigations, there may be an interest in completing the investigation
after the peak of transmission of the epidemic wave. However, a cross-sectional investigation,
conducted at any time of the epidemic, will provide important information that can be used to
inform public health responses.
For longitudinal cohort study with serial sampling, the epidemic curve from surveillance (daily
number of new confirmed cases) can be used to adjust the frequency with which samples are
collected to provide real-time estimates of seropositivity in the general population.
2.2 Study population
The geographic scope of the investigation should first be defined. This may be limited to a local or
regional investigation, or may be conducted as a national investigation. Within the geographic scope
of the study, high incidence and low incidence areas should be identified. The selection of these
areas should be informed by the latest information on COVID-19 virus circulation, available on the
WHO website.
The study population should then be identified in at least one high incidence and one low incidence
area through the random selection of households. For the purpose of this investigation, a household
is defined as a group of people (2 or more) living in the same residence. In practice, the technical
definition may vary due to social, political and cultural practices.
Definitions of a household which may be used (but are not limited to):
5