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  Table of Contents    
Year : 2023  |  Volume : 66  |  Issue : 2  |  Page : 431-432
The dilemma of choosing the optimum vaccine interval

1 Department of Microbiology, Saveetha Dental College and Hospital, Chennai, Tamil Nadu, India
2 Department of Microbiology, Dr. ALM PG Institute of Basic Medical Sciences, University of Madras, Chennai, Tamil Nadu, India

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Date of Submission08-Aug-2021
Date of Decision01-Oct-2021
Date of Acceptance06-Oct-2021
Date of Web Publication27-Apr-2022

How to cite this article:
Menon T, Balasubramanian R, Veeraraghavan GR, Perumal MN. The dilemma of choosing the optimum vaccine interval. Indian J Pathol Microbiol 2023;66:431-2

How to cite this URL:
Menon T, Balasubramanian R, Veeraraghavan GR, Perumal MN. The dilemma of choosing the optimum vaccine interval. Indian J Pathol Microbiol [serial online] 2023 [cited 2023 Jun 3];66:431-2. Available from:

Dear Editor,

The Covid-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to be a global threat. Vaccine strategies are important to contain the pandemic.[1],[2] According to a recent communication issued by the U.S. Food and Drug Administration (FDA), SARS-CoV-2 antibody tests should not be used to evaluate a person's level of immunity after COVID-19 vaccination. Yet, scientists in several countries are carrying out vaccine evaluation studies using validated serological assays. Antibody titers that indicate vaccine efficacy are currently not known.[3]

In India, majority of the vaccinated people have been administered the Serum Institute of India's Covishield vaccine. After the vaccine was licensed in January 2021, India adopted the 4–6 weeks' interval between the two doses. Subsequently, clinical trial data from other countries pointed to a better immune response when the gap was extended to 12 weeks and, presently, the recommendation followed in India is to administer the second dose at 12–16 weeks' interval (i.e., at least 84 days after administration of the first dose). The efficacy of the vaccine at various intervals is still under study and continues to be a gray area for want of robust supporting data. In a pilot study, we assayed the post-vaccination immune response in 91 staff and students in an educational institution using the Anti-SARS-CoV-2 IgG ELISA kit (EUROIMMUN MedizinischeLabordiagnostika AG) according to the manufacturer's instructions. The reagent wells of this kit are coated with an S1 domain of the spike protein of SARS-CoV-2 expressed recombinantly in the human cell line HEK 293. We detected optical density (OD) at 450 nm and evaluated the results semi quantitatively by calculating the OD ratio of each sample to that of the calibrator included in the kit.

Eighty-three of the 91 participants had been administered two doses of the Covishield vaccine at varying intervals ranging from 4 weeks to 16 weeks, and the last dose had been given 1–22 weeks prior to the collection of the sample. Antibody levels were detectable in participants from 1 week to 20 weeks after the second dose of the vaccine and peaked at 8 weeks [Figure 1]. The best antibody response as judged by the OD values were in participants who had taken the vaccine at a 7-week interval, followed by those who had taken it at intervals of 11 weeks and 16 weeks. However, we had only one participant in the 16-week interval group. The optimum interval between the two samples appeared to be 7–11 weeks [Figure 2]. Due to the small sample size and inadequate numbers representing each time interval, it was difficult to come to a precise conclusion. However, the data generated in this pilot study can be used to plan a larger and more rigorous investigation. Immune responses to vaccines are known to vary in different geographic regions[4] and data related to patients in India would be useful in planning guidelines and future strategies.
Figure 1: Antibody response at different periods postvaccination.

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Figure 2: Antibody response in relation to the interval between doses

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The authors wish to thank the Management, staff, and students of Saveetha Dental College for their support and participation in this study and to the University Grants Commission, New Delhi for providing funds for the purchase of the serological kit.

Financial support and sponsorship

The ELISA Euroimmun kit was purchased from research funds of a UGC funded project.

Conflicts of interest

There are no conflicts of interest.

   References Top

Amodio E, Capra G, Casuccio A, De Grazia S, Genovese D, Pizzo S, et al. Antibodies responses to SARS-CoV-2 in a large cohort of vaccinated subjects and seropositive patients. Vaccines 2021;9:714.  Back to cited text no. 1
Okba NMA, Müller MA, Li W, Wang C, Geurtsvan Kessel CH, Corman VM, et al. Severe acute respiratory syndrome coronavirus 2 − specific antibody responses in coronavirus disease patients. Emerg Infect Dis 2020;26:1478-88.  Back to cited text no. 2
Doria-Rose N, Suthar MS, Makowski M, O'Connell S, McDermott AB, Flach B, et al. Antibody persistence through 6 months after the second dose of mRNA-1273 vaccine for Covid-19. N Engl J Med 2021;384:2259-61.  Back to cited text no. 3
Choe YJ, Blatt DB, Lee HJ, Choi EH. Associations between geographic region and immune response variations to pneumococcal conjugate vaccines in clinical trials: A systematic review and meta-analysis. Int J Infect Dis 2020;92:261-8.  Back to cited text no. 4

Correspondence Address:
Thangam Menon
Professor Emeritus, Department of Microbiology, Saveetha Dental College and Hospital, 162, Poonamallee High Road, Velappanchavadi, Chennai - 600 077, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_800_21

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