Coronaviruses are a diverse group of viruses infecting many different animals, and th can
cause mild to severe respiratory infections in humans. At the end of 2019, a novel
coronavirus designated as SARS-CoV-2 emerged in Wuhan, China, and caused an outbreak of
unusual viral pneumonia. Being highly transmissible, this novel coronavirus disease, also
known as coronavirus disease 2019 (COVID-19), has spread fast worldwide. It has
overwhelmingly surpassed SARS and MERS regarding both the number of infected people and
the spatial range of epidemic areas. The ongoing outbreak of COVID-19 has posed an
extraordinary threat to global public health.

Studies in large cohorts of SARS-CoV-2 infected individuals indicate that antibodies to
the receptor-binding domain (RBD) of the viral spike glycoprotein appear within the first
three weeks from symptoms onset, and IgG and/or IgA seroconversion occurs either
sequentially or simultaneously with the appearance of IgM. Studies showed anti-RBD IgG in
95% of COVID-19 patients by the fourth week from symptom onset and observed that these
antibodies increased throughout follow-up until the third-month post-hospital discharge.
Moreover, the early presence of anti-RBD IgG and anti-spike IgA positively correlated
with patient survival and reduced persistence of SARS-CoV-2 RNA in nasopharyngeal swabs,
respectively. The spike glycoprotein mediates entry into target cells via the ACE2
receptor. Clinical trials with monoclonal antibodies (mAbs) against its RBD decreased
viral load in patients with recently diagnosed mild/moderate COVID-19.

Furthermore, anti-spike neutralizing antibodies (nAbs) produced by COVID-19 patients can
block viral infection of human cells in vitro and counter viral replication in vivo.
However, the impact of nAbs on the COVID-19 course is still controversial, with some
studies even suggesting either a detrimental role for nAbs in disease progression or
finding no nAbs differences among hospitalized patients who subsequently experienced
varying disease outcomes. Whether SARS-CoV-2 nAbs decline at a similar pace is yet to be
conclusively established.

Defining the antibody response to SARS-CoV-2 will be essential for understanding disease
progression, long-term immunity, and vaccine efficacy. Investigators designed a study
investigating the neutralizing antibody response among post-infected and post-vaccinated
individuals to determine how the spike protein neutralizing antibody correlates with
natural infection and vaccination and how mutations of viral strains affect associated
antibodies. New Taipei City Municipal TuCheng Hospital established a special infectious
pneumonia ward in May 2021 to treat patients infected with symptomatic SARS-CoV-2
patients. During the period, 97 patients were admitted and enrolled. In light of the
current timing of the pandemic, most published serological studies are predominantly
cross-sectional or, at most, include a longitudinal follow-up. Cognitive function and
PhenoAgeAccel will be examined for SARS-CoV-2 N and S titers decline trend analysis to
correlate long-COVID brain fog or early decline of N and S antibodies.

Therefore, investigators designed a three-year longitudinal study to detect
participantss' SARS-CoV-2 neutralizing and spike antibodies.