INTRODUCTION:
SARS Coronavirus-2 (SARS CoV-2) causing the COVID-19 pandemic has
undergone continuous genetic and antigenic evolution from the Wuhan
strain (Wu Hu-1) to numerous variants of concern (VOC)-Alpha, Beta,
Delta and recently, Omicron, resulting in global waves of infection. VOC
have shown higher replication efficiency, enhanced ACE2 receptor binding
and ability to evade immunity induced by natural infection or
vaccination.1 Mutations resulting in increased
replication fitness lead to higher viral loads of delta VOC as compared
to Wu Hu-1 and alpha variants.2 Recently emerged
variants (Omicron and its sub-lineages) have shown a higher replicative
fitness than delta.3
The infection spectrum (asymptomatic to severe) of SARS CoV-2 is similar
in children and adults, but children have fewer
symptoms,4 recover faster, with better prognosis and
fewer deaths overall.5 Children rarely manifest a
hyper-inflammatory severe illness - multisystem inflammatory syndrome in
children (MIS-C).6 It is based on this notion of
milder paediatric illness that covid-19 vaccines (Wu Hu-1-based or
bivalent boosters) have been widely approved for use globally in adults
and children >12 years of age.7
Real-time RT-PCR (rRT-PCR), the diagnostic modality of choice for
COVID-19 provides a Ct value readout that may be used as
a metric of virus load.8 Ct values
correlate poorly with severity,9 but have shown
improved relationship, with differences between
variants.10 Children have higher respiratory virus
loads compared to adults,11 but loads do not correlate
with severity.12 Presence of SARS CoV-2 specific
antibody (IgM/IgG) anti-spike antibodies indicates virus exposure and if
neutralising are considered a correlate of
protection.13 Levels of antibody correlate with severe
disease in adults.14 Children, respond to infection
with a robust, long-lasting immune response, which is skewed towards the
spike protein compared to nucleoprotein (unlike in adults), irrespective
of illness severity.15 Few studies have reported the
relationship of Ct value, antibody response and clinical
severity among adults and very limited among
children.16
To understand antibody dynamics in paediatric SARS CoV-2 infection, we
recruited PCR positive children across the infection spectrum
(asymptomatic to severe disease including MIS-C) during the wild-type
and delta waves in India. Sera
were tested for antibodies to
SARS CoV-2 nucleoprotein(anti-N) and spike(anti-S) proteins. We examined
the relationship of virus load at detection, clinical severity on
antibody levels (anti-N and anti-S) 4-6 weeks after infection. We
observed differences in virus load and antibody response between
wild-type and delta variants in mild-to-moderate disease.