In late December 2019, a new coronavirus strain emerged in Chinese megacity Wuhan. The World
Health Organization (WHO) named it Severe Acute Respiratory Syndrome Coronavirus 2
(SARS-CoV2) leading to coronavirus disease 2019 (COVID-19). On January 30, 2020 the
International Health Regulations Emergency Committee of the WHO declared the outbreak a
"public health emergency of international concern". On March 11, 2020 WHO characterized
COVID-19 as a pandemic and on March 14th, the Spanish President COVID-19 outbreak a "national
emergency" for second time in 40 years.

In order to fight this unanticipated pandemic, emergency measures have been implemented in
different countries such as lockdown, social distancing and testing. Massive community
testing to detect early or asymptomatic infections as well as social distancing has been used
in certain countries (South Korea, Iceland, etc..) with relatively success. In this sense,
Polymerase Chain Reaction (PCR) is considered to be the gold standard to diagnose the
infection with SARS-CoV2. On the other hand, Enzyme Linked ImmunoAssay (ELISA) has also been
widely used to determine the presence of antibodies (Immunoglobulins M, A and G) and, hence
immunological status. Some studies have reported the presence of IgM and IgA antibodies
within the first 5 days of clinical symptom onset, while IgG is usually detected on 14 days
after symptom onset, with a positive rate of 85.4%, 92.7% and 77.9%, respectively. Moreover,
a recent report of reveals that positive detection rate is significantly increased when
combined IgM/IgA ELISA assay with PCR for each patient compare with a single quantitative PCR
test. In this sense Igenomix has recently obtained the authorisation by the Valencia
Community Authority to provide these services after completing the requested process of
verification.

In this moment, when reopening phases are planning or even undertaken in the majority of
countries, the decision to enact any of these measures rests with the judgement of each
health care system. However, every country or individual community circumstances may be
unique and require contextual consideration based on three main factors: the severity of the
pandemic spread, the measures and timing implemented during the pandemic, and the moment of
the post pandemic that this population is in. Therefore, international metrics are urged to
guide the re-opening of the post pandemic era in different parts of the world to provide a
logical approach to mitigate risk to new outbreaks.

This is a retrospective, observational study in which anonymized data from subjects who
already performed PCR and ELISA test for COVID-19 detection at Igenomix, will be used to
assess the rate of immunized population as well as the rate of asymptomatic contagious
population in three hot spots of Spain (Madrid, Barcelona and Valencia) immediately after the
lockdown period. After data collection and processing, once the full anonymization process
has been completed, the pool of data will be analyzed with the aim of retrospectively
describe the immune and infective spectrum of illness from SARS-CoV-2 infection in the
general asymptomatic population in three main areas of Spain (Madrid, Barcelona and Valencia)
with high impact of COVID-19. Moreover, other additional descriptive variables such as age,
gender, etc will be assessed.

Being an observational retrospective study, the sample size would consist of the complete
database of individuals analyzed by ELISA and PCR from areas of Madrid, Barcelona and
Valencia representing approximately 1,000 cases. Waiver of informed consent form has been
duly authorized by the Ethic Committee in agreement to the local legislation.

No intervention involving patients or their biological material will be required.