*4.2. Strengths and Limitations*

This study used nationally representative data to investigate adult immunization coverage in India. To the best of our knowledge, this is the first study on nationwide adult immunization coverage. However, our study is limited by self-reported vaccination status which is susceptible to recall bias.

#### **5. Conclusions**

We observed a very low coverage of all vaccines among adults. Furthermore, the coverage was higher in affluent groups, depicting a disparity in accessing immunization. However, universal vaccination may not be feasible in India due to the huge population of at-risk groups and disadvantaged sections of society such as deprived strata and women, who need to be covered under the ambit of free immunization, which can help in achieving universal health coverage.

**Author Contributions:** Conceptualization, formal analysis, methodology, writing—original draft preparation, D.S.; conceptualization, formal analysis, methodology, writing—original draft preparation, A.S.; methodology, writing—review and editing, S.K.; methodology, writing—review and editing, S.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** No funds were received to conduct the present research.

**Institutional Review Board Statement:** The present study utilizes de-identified data from a secondary source. The data have been archived in the public repository of the LASI held at IIPS. The access to the data requires registration which is granted specifically for legitimate research purposes. The LASI received mandatory ethical approval from the Indian Council of Medical Research and the Institutional Review Board (IRB) held at IIPS, Mumbai. Data from the LASI are archived in a public repository; therefore, there is no need for additional ethical approval to conduct the present study. All methods were carried out in accordance with the relevant guidelines and regulations.

**Informed Consent Statement:** At the unit level, individuals were supplied with a catalogue containing the information on the purpose of the survey, confidentiality, and safety of health assessment. Written consent forms were administered at household and individual levels, in accordance with the Human Subject Protection. However, we used secondary anonymous data obtained from public source for the present study.

**Data Availability Statement:** The dataset analyzed during the current study is available in the LASI data repository held at ICT, IIPS https://iipsindia.ac.in/content/lasi-wave-I (accessed on 10 December 2022). Requests to access the data should be made to datacenter@ipsindia.ac.in.

**Acknowledgments:** The authors are grateful to the Longitudinal Ageing Study in India (LASI) for assembling and publishing accurate, nationally representative data on a range of health biomarkers and healthcare utilization indicators for the population in the age range of 45 years and older. The authors are also grateful to the LASI's project partners: the International Institute for Population Sciences (IIPS), Harvard, the T. H. Chan School of Public Health (HSPH), and the University of Southern California (USC).

**Conflicts of Interest:** The authors declare that they have no competing interests.
