 Abstract | | |
Background: As the world has been going through a pandemic of coronavirus disease 2019 (COVID-19) for the past two years, a safe and effective vaccine was urgently needed. Vaccination against the disease was launched in India on January 16, 2021 with healthcare workers, frontline workers, and the elderly above 60 years being the first beneficiaries. Vaccines being used in India are Covishield and Covaxin. Material and methods: Fifteen healthcare workers (HCWs) who were vaccinated with Covishield or Covaxin were included in the study, and T cell, B cell and antibody response of the HCWs were analyzed. Blood samples collected from every subject were sent for antibody analysis, hematological workup for cell counts, and flow cytometry was performed for various subsets of lymphocytes. Hematological variables in naïve HCWs (who never had any natural infection) and recovered HCWs (those recovered from natural infection) were compared. Results: Antibody index among recovered HCWs was significantly higher than the naïve HCWs. All the leucocyte parameters showed a higher median value in the recovered group except total leucocyte count (TLC), T helper cell count (Th cell), T helper cell to T cytotoxic cell (Th cell: CTL) ratio and natural killer (NK) cell. But only Th: CTL ratio showed a statistically significant difference. Conclusion: This study shows that the antibody index among individuals who had both vaccination and COVID-19 infection is significantly higher than those who just had vaccination. T helper cell to T cytotoxic cell ratio is lowered in the recovered HCWs as compared to the naïve HCWs and this finding is statistically significant.
Keywords: COVID-19, Covaxin, Covishield, immune response
How to cite this URL:
Kumar R, Singh S, Chawla R, Balhara K, Dhar L. COVID-19 vaccination: Immune response in healthcare workers—A study with review of literature. Indian J Pathol Microbiol [Epub ahead of print] [cited 2023 Sep 24]. Available from: https://www.ijpmonline.org/preprintarticle.asp?id=361289 |
| Introduction | |  |
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has caused a global pandemic, and thus a safe and effective vaccine was urgently needed. Strong, Th1-skewed T cell responses can drive protective humoral and cell-mediated immune responses and might reduce the potential for disease enhancement.[1],[2] Cytotoxic T cells clear virus-infected host cells and contribute to the control of infection.[3] Studies of patients infected with SARS-CoV-2 have suggested a protective role for both humoral and cell-mediated immune responses in recovery from COVID-19.[4],[5]
Vaccination against the disease was launched in India on January 16, 2021, with healthcare workers (HCWs), frontline workers, and the elderly above 60 years being the first beneficiaries. Two vaccines have so far been used in India: Covishield and Covaxin. The Covishield vaccine is a viral-vectored vaccine, developed by the Serum Institute of India in line with the vaccine developed in the UK by Jenner Institute, University of Oxford. Covaxin is an inactivated virus vaccine, developed by Bharat Biotech in collaboration with the Indian Council of Medical Research.[6]
During the early stages of vaccination, there were public concerns about the safety and efficacy of the vaccines. This was mainly due to the rapid approvals given to their usage.[7],[8] Subsequently, several scientific publications have validated the safety of these vaccines.[9] The efficacy as determined by seroconversion after the first and second doses of Covishield is 91% and 100%, respectively and that of Covaxin is 98.3% at 56 days post-vaccination.[10],[11]
This study describes, in detail, exploratory analyses of the immune responses in adults aged 22–50 years, 4–8 weeks after vaccination with two doses of Covishield or Covaxin in naïve HCWs and 4–8 weeks post clinical and serological recovery in recovered HCWs.
Replication-deficient adenovirus vectors or inactivated COVID-19 virus are potent inducers of both antibodies and cytotoxic T cells; the latter can clear virus-infected host cells and contribute to the control of infection, alleviating disease symptoms.[12] Importantly, high-frequency T cell responses targeting the SARS-CoV-2 spike protein have been detected in patients who recover from COVID-19, with recent data suggesting a role for T cells during COVID-19.[13],[14],[15]
Currently, there are no defined correlates of protection against COVID-19 infection, and the immunological thresholds required for vaccine efficacy remain undefined.[16] Clinical studies have suggested a protective role for both humoral and cell-mediated immunity in recovery from SARS-CoV-2 infection.[17]
This study compares T cell, B cell, and antibody response in those fully vaccinated HCWs against COVID-19 and those who got infected even after being fully vaccinated.
| Material and Methods | | |
Between February 2021 and April 2021, 15 HCWs were vaccinated with Covishield or Covaxin. All of them received two doses of 50 μg within a duration of one month. The study population consisted of healthy males and non-pregnant females with a median age of 28 years (range 22–50 years) with female preponderance. The study focused on T cell, B cell, and antibody response. Informed consent and detailed history were taken from the subjects. Peripheral venous blood of 3 ml was collected in a plain vial with a clot activator from the study subjects. Serum was separated and tested for the presence of total SARS-CoV-2 antibodies using WantaiTM SARS-CoV-2-Ab ELISA kit, an enzyme-linked immunosorbent assay (ELISA) for semiquantitative detection of total antibodies to SARS-CoV-2 virus in human serum or plasma specimens. The assay is a two-step incubation antigen “sandwich” enzyme immunoassay, which uses polystyrene microwell strips pre-coated with recombinant SARS-CoV-2 antigen. The sensitivity and specificity of the assay have been reported to be 94.5% and 100%, respectively, as per the kit literature. Another sample of 3 ml in EDTA anti-coagulated vial was used for hematological workup. Sampling and processing of samples were done four to eight weeks after vaccination with two doses of Covishield or Covaxin in naïve HCWs while four to eight weeks post clinical and serological recovery in recovered HCWS. In hematology lab blood sample was run on blood routine-analyser (Sysmex XN1000i, SYSMEX Corporation, Kobe City, Japan) for cell counts, peripheral smear was made, stained in giemsa, and the rest of the sample was kept for flow cytometry. Total leucocyte count (TLC) and differential count of peripheral blood were noted. Flow cytometry was performed on three lasers, five-color flow cytometer (Cytomics FC 500, Beckman Coulter, Inc., California, USA) to assess lymphocyte subsets in peripheral blood. TLC, absolute lymphocyte count (ALC), absolute T lymphocyte count (ATLC), absolute B lymphocyte count (ABLC), absolute natural killer cell (NK cell) count, absolute T helper cell count (Th) and absolute cytotoxic cell count (CTL) were analyzed, and ratios of Th/CTL were calculated.
For analysis of lymphocyte subsets according to flow cytometry results, CD45 positivity refers to lymphocytes and CD3 positivity refers to T lymphocytes (Th: CD3+/CD4+; CTL: CD3+/CD8+). CD19 positivity refers to B cells and CD56/CD16 positivity refer to NK cells. Following panel of antibodies were used: CD10, CD19, CD20, CD38, CD3, CD4, CD5, CD7, CD8, CD16, and CD56.
Statistical analyses were performed using IBM SPSS 26. Medians, means, ranges, standard deviation, and standard errors were calculated for each immunohematological parameter. Student's t-test was used to compare the distribution of the lymphocyte subsets between naïve and recovered HCWs. A two-tailed P value of ≤0.05 was considered significant.
| Results | | |
In this study, fifteen HCWs were studied, three of them were vaccinated with Covaxin and twelve were vaccinated with Covishield. All of them received two doses of vaccine (50 μg) within four to seven weeks duration, except one subject whose second dose was delayed due to corona infection after the first dose of vaccine. Out of fifteen HCWs who were fully vaccinated, eight got infected with coronavirus within four to seven weeks of the second dose except one case who got infected after twelve weeks. Out of these eight, three subjects had a history of corona infection, prevaccination [Table 1]. The age of the subjects ranged from 22 to 50 years, with a median age of 28 years. Adverse reactions noted postvaccination included pain/soreness in 66.7% (10/15) at injection site as most common, whereas fever in 33.3% (5/15), headache in 33.3% (5/15), myalgia in 26.7% (4/15), and fatigue in 20% (3/15). Majority of adverse events resolved in three to four days without significant morbidity and treatment.
In the naïve HCWs group, TLC ranged from 4300 to 10360/mm3 with a median of 7700/mm3, ALC ranged from 1317 to 3700/mm3 with a median of 1540/mm3, ATLC ranged from 859 to 2627/mm3 with a median of 1092/mm3, ABLC ranged from 127 to 573/mm3 with a median 294/mm3, T helper cells ranged from 347 to 1200/mm3 with a median of 735/mm3, T cytotoxic cells ranged from 232 to 1114/mm3 with a median of 458/mm3, T helper cell to T cytotoxic cell ratio ranged from 0.9 to 2.89 with a median of 1.4, NK cells ranged from 0 to 113/mm3 with a median of 57/mm3 and antibody index ranged from 13.43 to 19.14 with a median of 16.06 [Table 2] and [Figure 1]. (reference range[18]) | Table 2: Various parameters studied in HCWs (per mm3) (reference range[18])
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 | Figure 1: (a): Gating for lymphocytes (CD45 expression versus side scatter) on flow cytometry graph in naïve HCW. (b): CD3 expression versus CD4 expression on flow cytometry graph in naïve HCW. (c): CD4 expression versus CD8 expression on flow cytometry graph in naïve HCW. (d): CD3 expression versus CD56 expression on flow cytometry graph in naïve HCW
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In the recovered HCWs group TLC ranged from 6120 to 8130/mm3 with a median of 7210/mm3, ALC ranged from 1507 to 3175/mm3 with a median of 2231/mm3, ATLC ranged from 1020 to 2711/mm3 with a median of 1687.5/mm3, ABLC ranged from 174 to 387/mm3 with a median of 318.5/mm3, T helper cells ranged from 290 to 1326/mm3 with a median of 612/mm3, T cytotoxic cells ranged from 385 to 1149/mm3 with a median of 781/mm3, T helper cell to T cytotoxic cell ratio ranged from 0.5 to 1.76 with a median of 0.88, NK cells ranged from 0 to 136/mm3 with a median of 18.5/mm3, and antibody index ranged from 17.43 to 19.5 with a median of 19.14 [Table 2] and [Figure 2]. | Figure 2: (a): Gating for lymphocytes (CD45 expression versus Side scatter) on flow cytometry graph in recovered HCW. (b): CD3 expression versus CD4 expression on flow cytometry graph in recovered HCW. (c): CD4 expression versus CD8 expression on flow cytometry graph in recovered HCW. (d): CD3 expression versus CD56 expression on flow cytometry graph in recovered HCW
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| Discussion | | |
There have been very few studies on the postvaccination immune status assessment of recipient's lymphocyte and antibody response and negligible study on the HCWs, who bore the brunt of the pandemic for 18 months. We studied the immune response of fifteen fully vaccinated HCWs, out of which eight got infected with COVID-19 postvaccination. Thirteen out of fifteen subjects were females. The age of the subjects ranged from 22 to 50 years with a median age of 28 years. All the subjects (8 out of 15) who got infected with COVID-19 developed mild disease. Adverse reactions noted postvaccination included pain/soreness (66.7%) at the injection site as the most common symptom followed by fever (33.3%), headache (33.3%), myalgia (26.7%), and fatigue (20%). Majority of adverse events are resolved in three to four days.
Kataria et al.[19] reported similar adverse events, pain (62.7%) and soreness (24.1%) at the injection site as the most common symptoms, whereas fever (48.4%), headache (43.4%), myalgia (38.4%), fatigue (33.4%), joint pain (27.0%), and nausea (16.0%) were the most common solicited systemic adverse events on day one. Majority of local and systemic adverse events were seen in the first two days postvaccination and thereafter they resolved.
In this study, semiquantitative detection of total antibodies to recombinant antigen of SARS-CoV-2 was performed using WantaiTM SARS-CoV-2-Ab ELISA kit.
This study showed that antibodies index ranged from 13.43 to 19.14 with a median of 16.06 in the naïve HCWs group and ranged from 17.43 to 19.5 with a median of 19.14 in recovered HCWs group. This postvaccination antibodies study indicates that antibody index among vaccinated and COVID-19 recovered HCWs was higher as compared to naïve HCWs who were not naturally infected, and this was statistically significant (P value = 0.015) [Table 3]. | Table 3: Statistical analysis of various parameters in naïve HCWs vs recovered HCWs
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Among the 515 HCW (305 Male, 210 Female) studied by Singh K.A et al.,[20] 425 had received Covishield and 90 were Covaxin recipients and showed seropositivity of 98.1% and 80.0%, respectively after two doses. However, both seropositivity rate and median (IQR) rise in anti-spike antibody were significantly higher in Covishield versus Covaxin recipient (98.1 versus 80.0%; 127.0 versus 53 AU/mL; both P < 0.001). In a study by Jeewandara et al.,[21] SARS-CoV-2 antibodies analysis was carried out in 607 naïve and 26 previously infected HCWs, 28 to 32 days following a single dose of the Covishield vaccine. Around 92.9% of previously naïve HCWs seroconverted after a single dose of the vaccine, irrespective of age and gender; and ACE2 blocking antibodies were detected in 67/69 (97.1%) previously naïve vaccine recipients. The ACE2blocking titers measured by the surrogate neutralization assay significantly increased (P < 0.0001) from a median of 54.1 to 97.9% of inhibition, in previously infected HCWs.
Kataria et al.[19] evaluated 1638 HCWs two weeks postvaccination with Covishield (1 dose). Serostatus improved from 48.2% positive at baseline to 79.0% positive two weeks following the first dose of vaccination. After the first dose of vaccination overall higher percentage (98.2%) of seropositivity rates were observed in those with a history of COVID 19 disease.
In the study by Guang Yang et al.,[22] there were 66 COVID-19 patients, which included 26 mild cases, 19 moderate cases, and 21 severe/critical cases. Mild cases of COVID-19 showed ALC ranged from 1310 to 2370 mm3, T helper cells ranged from 375 to 884 mm3, T cytotoxic cells ranged from 306 to 679 mm3 with T helper cells to T cytotoxic cells ratio ranging from 0.82 to 1.82. Thus, mild cases showed similar findings as the current study.
This study showed that in the naïve HCWs group TLC ranged from 4300 to 10360/mm3 with a median of 7700/mm3, ALC ranged from 1317 to 3700/mm3 with a median of 1540/mm3, ATLC ranged from 859 to 2627/mm3 with a median of 1092/mm3, ABLC ranged from 127 to 573/mm3 with a median of 294/mm3, T helper cells ranged from 347 to 1200/mm3 with a median of 735/mm3, T cytotoxic cells ranged from 232 to 1114/mm3 with a median of 458/mm3, T helper cell to t cytotoxic cell ratio ranged from 0.9 to 2.89 with a median of 1.4, NK cells ranged from 0 to 113/mm3 with a median of 57/mm3.
In the recovered HCWs group TLC ranged from 6120 to 8130/mm3 with a median of 7210/mm3, ALC ranged from 1507 to 3175/mm3 with a median of 2231/mm3, ATLC ranged from 1020 to 2711/mm3 with a median of 1687.5/mm3, ABLC ranged from 174 to 387/mm3 with a median of 318.5/mm3, T helper cells ranged from 290 to 1326/mm3 with a median of 612/mm3, T cytotoxic cells ranged from 385 to 1149/mm3 with a median of 781/mm3, T Helper cell to t cytotoxic cell ratio ranged from 0.5 to 1.76 with a median of 0.88, NK cells ranged from 0 to 136/mm3 with a median of 18.5/mm3.
This study compared the TLC, ALC, ATLC, ABLC, T helper cell, T cytotoxic cell, and NK cell in naïve HCWs and recovered HCWs and found no significant difference between them. Only T helper cell to T cytotoxic cell ratio came out to be significant between naïve and recovered HCWs with lower ratio seen in recovered HCWs (P value of 0.043) [Table 3].
| Conclusion | | |
COVID-19 infection can prove to be deadly and thus an effective and safe vaccine is needed to end this pandemic and save millions of lives. Vaccination with Covishield and Covaxin showed seroconversion in all the HCWs studied. Antibody index among recovered HCWs was significantly higher than the naïve HCWs. All the leucocyte parameters showed a higher median value in the recovered group versus naïve group except TLC, Th cell, Th cell: CTL ratio, and NK cell. But only T helper cell to T cytotoxic cell ratio showed statistically significant difference between naïve HCWs and recovered HCWs.
Thus, this study shows that antibody index among individuals who had both vaccination and COVID-19 infection is significantly higher than those who just had vaccination. T helper cell to T cytotoxic cell ratio is lowered in the recovered HCWs as compared to the naïve HCWs, and this finding is statistically significant. As this virus is an enigma that is yet to be resolved, these findings when done on a larger cohort as longitudinal studies will help to understand and solve this puzzle better.
Limitation of this study is that it is a very small cohort and not a longitudinal study and due to safety concerns flow cytometry could not be done during the active infective stage.
Declaration of patient consent
The authors certify that they have obtained all appropriate subject consent forms. In the form the subject(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The subjects understand that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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Correspondence Address:
Sarika Singh,
Department of Pathology, Maulana Azad Medical College, New Delhi
India
 Source of Support: None, Conflict of Interest: None DOI: 10.4103/ijpm.ijpm_126_22
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3] |
