Seroconversion and safety of Covid-19 vaccines in pa-tients with chronic liver disease and liver transplant: A systematic review

Background and Aims: As part of the COVID-19 control strategy, a growing number of vaccine portfolios evolved and got fast-tracked through regulatory agencies, with a limited examination of their efficacy and safety in vulnerable populations, such as patients with chronic conditions and immunocompromised states. Patients with chronic liver disease (CLD), and cohorts post liver transplant (LT) in particular, were underrepresented in the determinant trials of vaccine development, hence the paucity of data on their efficacy and safety in published literature. This systematic review aims to examine the available evidence and ascertain the effectiveness and safety of Covid-19 vaccination in patients with CLD and those with LT. Methods: A systematic review of PubMed (Medline), Google Scholar, Cochrane Library, and ScienceDirect from inception until 1st March 2022 was conducted. We included observational studies and assessed vaccine efficacy regarding seroconversion or immunological rate, whereas serious or significant adverse effects have been considered safety outcomes when reported. Results: Studies comprised 45275 patients, performed in 11 different countries. Seroconversion or immunological rate after Covid-19 vaccination was mostly the primary endpoint, whereas other endpoints like covid-19 related adverse effects were also reported. Twenty-four of the final analyzed studies are prospective cohort studies, while four are retrospective cohort studies. Twenty-one studies included patients who underwent LT and received the Covid vaccine; nine included patients who had CLD due to various etiologies. The median age range of all included patients varied from 43–69 years. All patients with LT who received at least two doses of Covid vaccine had a seroconversion rate of around 60%. Patients with CLD had a seroconversion rate of about 92% post two doses of Covid vaccination. The average seroconversion rate in post-transplant recipients was around 45% after two doses of the significant Covid vaccines: Pfizer, AstraZeneca, Moderna, and Jansen. Only two studies have reported a higher seroconversion rate of 75% and 73% after the third dose of Covid vaccine. No significant adverse effects were reported in all studies; the most commonly reported negative effect was local injection site pain. Conclusion: The present systematic review, comprising real-world observational data studies, concludes that Covid-19 vaccination was associated with 92% and 60% seroconversion rates in patients with CLD and LT, respectively. No significant side effects were reported in all studies. This finding helps to resolve the uncertainty associated with Covid-19 vaccination in this cohort of patients.

Background and Aims: As part of the COVID-19 control strategy, a growing number of vaccine portfolios evolved and got fast-tracked through regulatory agencies, with a limited examination of their efficacy and safety in vulnerable populations, such as patients with chronic conditions and immunocompromised states.Patients with chronic liver disease (CLD), and cohorts post liver transplant (LT) in particular, were underrepresented in the determinant trials of vaccine development, hence the paucity of data on their efficacy and safety in published literature.This systematic review aims to examine the available evidence and ascertain the effectiveness and safety of Covid-19 vaccination in patients with CLD and those with LT.Methods: A systematic review of PubMed (Medline), Google Scholar, Cochrane Library, and ScienceDirect from inception until 1 st March 2022 was conducted.We included observational studies and assessed vaccine efficacy regarding seroconversion or immunological rate, whereas serious or significant adverse effects have been considered safety outcomes when reported.Results: Studies comprised 45275 patients, performed in 11 different countries.Seroconversion or immunological rate after Covid-19 vaccination was mostly the primary endpoint, whereas other endpoints like covid-19 related adverse effects were also reported.Twenty-four of the final analyzed studies are prospective cohort studies, while four are retrospective cohort studies.Twentyone studies included patients who underwent LT and received the Covid vaccine; nine included

INTRODUCTION
The first case of Coronavirus disease 2019 (Covid-19) was identified in Wuhan, China, on December 2019. 1 It quickly escalated to engulf the world and become a pandemic affecting every human at every phase of life, impacting politics, economics, and social policies.The beginning of the Covid-19 pandemic also led to a new era of realization that technological advancements had made it possible to create a vaccine in a year.However, it gave rise to numerous questions along the way.While due importance was given to the development of covid-19 vaccines at a rapid pace, most of these covid-19 vaccines were approved for emergency use without the data of their efficacy and side-effect profile in patients with various co-morbidities and chronic disorders, including patients with cirrhosis, chronic kidney disease, cardiovascular and chronic respiratory diseases as Seroconversion and safety of Covid-19 vaccines in patients with CLD and LT developed and validated cirrhosis severity scoring system that uses a patient's laboratory values for serum bilirubin, serum creatinine, and the international normalized ratio (INR) to predict three-month survival.In patients with cirrhosis, an increasing MELD score is associated with increasing severity of hepatic dysfunction and three-month mortality risk.A modified MELD score, called MELD-Na, recently became the standard for organ allocation for liver transplantation (LT); MELD-Na score takes into account Na values of 125-137. 17ovid-19 results in a strong humoral and cellular immune response. 18Antibodies (IgG and IgM) are classically detected in the second week of symptom onset, with IgM antibody appearing first and IgG being the most durable.Among the Covid-19 structural proteins, the Spike (S) and the Nucleocapsid (N) proteins are the main immunogens. 19The S protein consists of two subunits, S1, which contains the Receptor Binding Domain (RBD) and S2.Most available vaccines include only a fragment of the spike protein and induce antibodies to S, particularly the RBD on the S1 subunit of the spike protein. 20The Anti-RBD (or Spike) antibodies prevent the virus from penetrating the cells by inhibiting its binding to the Angiotensin-Converting Enzyme-2 (ACE-2) receptor in the epithelial cells of several human organs and tissues.Cellular immune responses against the virus, although considered essential to control the infection, are not commercially available but have been used for research purposes.Kulkarni et al.'s systematic review observed increasing Covid-related mortality, especially in liver transplant (LT) patients. 21It was also observed that cirrhotic patients' especially those with acute-onchronic liver disease and those with higher Child class and MELD scores as well as high serum creatinine levels, had higher mortality rates due to Covid-19. 3Therefore, vaccinating these individuals is of paramount importance.But data regarding CLD and the effect of vaccinations on these patients remains scarce, and the question remains unanswered related to vaccine efficacy and sideeffects concerns.Therefore, we aimed to conduct a systematic review based on already available data to determine if the efficacy and side-effect profile of Covid-19 vaccines on these particular patients' populations could be established.

Research question addressed
This systematic review was performed according to PRISMA 2021 guidelines. 22The systematic review protocol was formed before undertaking the data collection but needed to be registered.It is linked in the appendix.The research questions were: What is the effect of Covid-19 vaccines (mRNA, inactivated virion, viral vector, protein subunit vaccines) on efficacy, immunogenicity, and side effects in CLD and LT patients?

Eligibility criteria
We used the population-intervention-comparatoroutcomes (PICO) framework to establish the eligibility criteria.

Outcome
Efficacy and immunogenicity with antibodies development and reported adverse effects of Covid-19 vaccines in CLD and LT patients.We included all studies regardless of the bioanalytical methods for the determination of immunogenicity (such as Enzyme-Linked Immunoassay (ELISA), antibody assays, Chemiluminescence immunoassay [CLIA], Electrochemiluminescence immunoassay [ECLIA], etc.).

Inclusion and exclusion
We have included all prospective and retrospective studies in patients with CLD or liver transplantation except case reports and case series.References from various studies were also reviewed.All studies in English were included as the reviewer's primary VOL.2023 / ART.21   Seroconversion and safety of Covid-19 vaccines in patients with CLD and LT language of communication.All case reports, case series and analyses in languages other than English were excluded.All studies with healthy patients and animal studies were excluded.

Search strategy
Two reviewers independently performed a comprehensive search (A.A and M.E).PubMed (Medline), Google Scholar, Cochrane Library, and ScienceDirect included databases.We integrated controlled vocabulary (e.g., "Covid-19 Vaccines"[All Fields] OR "COVID-19 Vaccines"[MeSH Terms] AND liver disease OR cirrhosis OR liver transplant) and keywords (e.g., Covid-19 vaccines and CLD or cirrhosis or LT) into the searches.The comprehensive search strategy is included in the appendices for reference.Limits and filters used were language restriction to English language only and date restriction to 1 st January 2020 till 1 st March 2022.We also performed a manual reference search from pre-existing and retrieved studies.

Screening
The screening was done in two stages, with an initial title and abstract screening attempted by two reviewers independently (A.A and M.E).Articles were eligible for full-text review if they included any terms related to covid-19 vaccines and liver disease or liver transplantation.Eligible papers were then evaluated for inclusion; any discrepancy in the study selection was clarified by mutual discussion, and if still not settled by discussion, a third reviewer (A-EZ) resolved the disagreement as guided by the protocol.The PRISMA flow diagram shown in Figure 1 depicts our search methodology.

Figure1. PRISMA flow diagram.
Seroconversion and safety of Covid-19 vaccines in patients with CLD and LT

Quality appraisal with risk of bias assessment
Quality appraisal was done with standardized tools, namely Newcastle Ottawa Scale tool, for assessing the quality and risk of bias in cross-sectional and cohort studies.Quality appraisal of studies included in data synthesis is shown in Table 1.

Data extraction
Data extraction was performed utilizing preplanned templates.Data extracted included author, year of publication, study design, country, median age, patient population, control, outcome assessed, type of vaccine, and significant adverse effects.

RESULTS
Our screening initially revealed 2496 titles.After removal of duplicates, reviews, and meta-analysis, it yielded 1645, which were screened.After screening, 28 studies were included in our final review (Figure 1 shows the PRISMA flow diagram).−47 Four studies were retrospective, while the rest were prospective studies Table 1).Studies comprised 45275 patients considered in our review; patients included in our review either have CLD (cirrhosis) or post-liver transplantation.Analyses were performed in 11 different countries, and the median age range of all included patients varied from 43 to 69 years.Seroconversion or immunological rate after Covid-19 vaccination was mostly the primary endpoint, whereas other endpoints like Covid-19-related adverse effects were also reported.Twenty-one studies included patients who underwent LT and received the Covid-19 vaccine; the rest had CLD due to various etiologies.Table 1 summarizes the CLD and LT patients' characteristics, study designs, type of used vaccines, serological response rates, and significant adverse events of vaccines.All patients with LT who received at least two doses of the Covid-19 vaccine had a seroconversion rate of around 60%. Patients with CLD had a seroconversion rate of about 92% post two doses of Covid-19 vaccination.Two Del Bello et al. 23 and Kamar et al. 31 reported a higher seroconversion rate of 73% and 75%, respectively, after the third dose of the Covid-19 vaccine.No significant adverse effects were reported in all studies; the most reported adverse effects were local injection site pain; however, no derangements of liver function tests or liver-related complications were reported.Table 2 shows the status of Covid-19 infection exposure, etiology of CLD, indication for LT, and types of antibodies measured in the population of the included studies.

DISCUSSION
The finding of this review represents the first comprehensive examination of published reports on the effect of Covid-19 immunization in patients with CLD patients with cirrhosis.Our qualitative synthesis of n = 45275 patients amongst 28 studies found that patients with CLD had seroconversion rates of about 92% after receiving two doses of Covid-19 vaccination.A subset of those with LT had a comparatively lower seroconversion rate of approximately 60%.From previous reports, patients with CLD have suboptimal innate and humoralmediated responses to infective agents, making a seroconversion rate of 92%; therefore, both are reassuring, especially in the absence of significant vaccine-related adverse events.Constituents' studies in our synthesis have reported variable seroconversion proportions but with uniform rates amongst patients with CLD. 49There was no difference in seroconversion response among cirrhotic and non-cirrhotic groups. 49his undoubtedly will have tremendous implications regarding the need and immunization schedules of these vulnerable cohorts of patients.Studies thus far involving various Covid-19 patient cohorts have consistently demonstrated a poorer outcome for those with liver diseases of varying primary etiologies compared to those without. 50With the onset of the Covid-19 pandemic, several SARS-COV vaccines have been developed at a geometric pace, with subsequent review and multi-level, and sometimes     53 This mirrors our observation in these pooled analyses.Similarly, the proportion of patients with adverse events following vaccination was negligible, consistent with previous reports, including those by Tu et al. 54 In common with earlier reports, we found fatigue and dizziness remained the most reported adverse effects following COVID-19 vaccination.

Strength and limitations
Our review represents the first and the most comprehensive pooled examination of the estimates of seroconversion rates amongst patients with CLD and LT following COVID-19 immunization.Our finding of differential point estimates amongst these two populations will undoubtedly be both reassuring and provide a supporting level of evidence for consideration of booster vaccine doses in the later cohort of patients.Our observation of excellent safety profiles across vaccine formulations in this hitherto pharmacologically vulnerable population is reassuring.Consistent with previous reviews examining this variability in transplant patients, we encountered several limitations in this synthesis, including differences in the design of constituent studies, differences in the bioanalytical determination of patient-specific approval by regulatory agencies worldwide (including the FDA).These include Pfizer/ BioNTech BNT162b2 mRNA 7 Moderna mRNA-1273, 8 and the AstraZeneca/University of Oxford ChAdOx1-nCoV-19 chimpanzee adenovirus (ChAd). 9Although these vaccines reported excellent efficacy and safety profiles in healthy individuals, uncertainty remains regarding their effectiveness and safety in patients' cohorts with CLD.This arose from the paucity of available data and the small sample size of the few studies exploring this.For example, despite thousands of patients enrolled in these trials, there is conspicuous underrepresentation of the proportion of those with CLD.In the Pfizer vaccination study, for example, 217 (0•6%) of 37706 participants had liver disease, and only three (<0•1%) had moderate to severe liver disease.A similarly low proportion of patients with CLD were included in the Moderna trial (196 of 30351 patients [0•6%]).Indeed, the ChAdOx1-nCoV-19 vaccine trial excluded patients with pre-existing liver disease.
Our finding of comparatively lower seroconversion rates (60%) amongst patients with LT was rather interesting.This observation appears consistent with those of Thuluvath et al., 49, who reported a failed response rate following Johnson and Johnson vaccination of 61% and 24% for liver transplant recipients and those with CLD, respectively.Compared to other solid organ transplants (such as patients with Kidney transplants), our point estimate of seroconversion rates appears satisfactory, with 19% to 25% reported in some studies. 51athophysiologically, this could be attributable to the pervading induced immune tolerance obligated by the many immunosuppressive pharmacological agents these patients often have to take.

Table 1 . Characteristics of the studies included in this review.
Seroconversion and safety of Covid-19 vaccines in patients with CLD and LT VOL. 2023 / ART.21

Table 2 . (Cont.)
31,47A combination of other factors, including disordered inflammatory response and tardiness of B-cell response, are expected to impact the immunogenicity of administered vaccines negatively.Reassuringly both our review and recently published reports have all suggested otherwise.It is reassuring that these points estimate lies within the ballpark reported in other related morbidities characterized by underlying disease-related or pharmacologically induced immune modulation and exposure to COVID-19 vaccination.The overall pooled point estimate of seroconversion response from our review falls within the reported