Introduction
The COVID-19 pandemic has continued for more than two years infecting
half of the world population either by natural infection or by
vaccination. More than 760 million people have been infected and about
6.9 million deaths have occurred owing to SARS-CoV-2 infection as of
April 2023.1 The available vaccines in India at the
time of study were the Astra Zeneca (ChAdOx1 nCoV-19) vaccine
(Covishield, Oxford/Astra Zeneca COVID-19 AZD1222, Serum Institute of
India), a non-replicating viral vector vaccine (NRVV) and Bharat biotech
BBV152 (Covaxin [BBV152]) containing inactivated whole virus; both
of which required two doses for effective action. Covishield vaccine
uses modified viral vector platform of chimpanzee adenovirus (ChAdOx1)
that permits it to transfer spike protein of COVID-19 virus into human
cells. Study based on the in-vitro live-virus neutralization and T-cell
immune responses to the spike protein, showed that the efficacy of two
doses of Covishield vaccine against moderate-to-severe COVID-19 was
~ 81.5%.3 Multiple studies have
quoted that after natural SARS-CoV-2 infection or vaccination, vigorous
T-cells response is responsible for production of anti-spike
Neutralizing antibodies against multiple viral epitopes like spike
Anti-receptor binding domain (RBD) & N-Terminal domain
(NTD).4-6 The mRNA and adjuvant vaccines promote
intracellular production of spike protein which is presented by antigen
presenting cells to naïve T-cells (both CD8+ and CD4+ T cells) causing
activation and differentiation of T-cells into effector cells and
different subsets of memory T-cells. These memory cells once invoked
either by natural infection or by vaccination, can persists even after
decades. The interplay of this cellular and humoral response is
essential for effective immunity.7-9
Vaccination against COVID-19 has reduced the severity of the disease,
yet we are still facing waves of COVID-19 infection like the recent
surge in China and India.10,11 Demand for booster dose
is brought up with each wave of COVID-19, especially in vulnerable
population like elderly, cancer patients and immunocompromised
population.12 Studies have monitored the titer of
neutralizing antibody at different time interval to check for adequate
humoral immune response in healthy individuals.13-15Few studies have mentioned waning effect of humoral response at six
months of vaccination by measuring IgG neutralizing antibodies (NAb) levels and proposed that reactivity & durability of cellular response (
CD8+ cells) can prevent severe disease against viral variant even when
they escape from Nab. Equally, T-cell response at different time period
has also been studied in healthy individuals. 4,16,17But there is paucity of data in immunocompromised individuals for
sustained immune response especially with regards to T-cell-based
immunity. Cirrhosis is associated with impairment of innate and adaptive
immune system leading to acquired immunodeficiency. Both B and T-cell
mediated immunity is hampered in form of B and T-cell depletion and
dysfunction because of multifactorial causes like impaired production,
proliferation and increased apoptosis.18,19 Hence, we
selected patients of cirrhosis as immunocompromised population in our
study. We studied different subset of T-cell memory cells along with
antibody titer at baseline and at one year duration in vaccinated
healthy individuals and patients with liver cirrhosis at one year to
observe any difference in immune response.