**3. Results**

This study was based on 31,464 participants aged ≥60 years with a mean age of 68.87 ± 7.51 years. Almost half of the participants (58.51%) were 60–69 years of age (Table 1). We observed a female predilection (52.55%) in the study population. Around 70.55 of the respondents lived in rural areas. We found that 43.48% of the participants had formal education and 74.06% of respondents were currently employed. We observed that 18.24% of the participants had health insurance coverage.

The overall coverage of the diphtheria and tetanus vaccine (2.75% (95% CI: 2.75–3.12)) was highest, followed by the typhoid vaccine (1.84% (95% CI: 1.69–1.99)), hepatitis B vaccine (1.82% (95% CI: 1.67–1.97)), influenza vaccine (1.59% (95% CI: 1.45–1.73)), and pneumococcal vaccine (0.74% (95% CI: 0.65–0.84)). Further, it was observed that the participants from the most affluent group had a higher coverage of adult vaccinations compared to any other group. Diphtheria and tetanus vaccines were mostly (4.21%) taken by the most affluent group. The pneumococcal vaccine had the minimum coverage among the most deprived group, i.e., only 0.16% (Table 2).


**Table 1.** Characteristics of the study population.

**Table 2.** Coverage of various adult vaccines across wealth quintiles among older adults in India.


The adjusted multi-variable model revealed that the most affluent group had a higher chance of getting vaccinated for influenza (AOR: 3.32 (95% CI: 2.52–4.39)), pneumococcal

(AOR: 5.53 (3.41–8.99)), hepatitis B (AOR: 5.24 (95% CI: 3.99–6.87)), typhoid (AOR: 3.53 (95% CI: 2.65–4.70)), and diphtheria and tetanus (AOR: 3.60 (95% CI: 2.96–4.39)) than the most deprived group (Table 3).

**Table 3.** Association between uptake of various adult vaccines and wealth quintiles among older adults in India.


Adjusted for age, sex, residence, caste, occupation, and health insurance.

It was found that respondents with psychiatric problems (5.28%) followed by high cholesterol (3.69%), multimorbidity (2.59%), and stroke (2.46%) had taken influenza vaccines more than participants having other selected chronic conditions. Pneumococcal vaccination coverage was observed to be higher among respondents having high cholesterol (2.56%) followed by psychiatric problems (2.29%) and cancer (2.20%). The coverage for the hepatitis B vaccine was found to be higher in respondents with high cholesterol (5.53%) followed by cancer (5.51%) and psychiatric problems (5.06%). Typhoid vaccination coverage was found to be higher in respondents having high cholesterol (4.59%) followed by psychiatric problems (5%) and cancer (4.46%). Respondents with high cholesterol (10.05%) followed by psychiatric problems (6.86%) and cancer (6.84%) had higher coverage of diphtheria and tetanus vaccines (Table 4).

**Table 4.** Coverage of adult vaccines across selected non-communicable diseases among adults in India.



**Table 4.** *Cont.*

#### **4. Discussion**

The overall coverage of adult vaccination was considerably low among the participants belonging to deprived groups. The highest coverage was of the DT vaccine followed by those of typhoid, hepatitis B, influenza, and pneumococcal. Participants having high cholesterol, psychiatric conditions, and cancer had the highest coverage for all vaccines.

We observed that the DT vaccine had the highest coverage followed by typhoid, hepatitis B, influenza, and pneumococcal vaccines. A recent facility-based study conducted at an adult vaccination center in Jodhpur observed that tetanus toxoid, anti-rabies, and yellow fever vaccines had the highest coverage [1]. However, the coverage of the hepatitis B vaccine (8%), followed by the pneumococcal vaccine (7%) and typhoid vaccine (3%) was reported higher than the findings of our study [1]. Interestingly, the coverage of the influenza vaccine (1%) was found to be lower compared to the present study. Notably, there is a dearth of literature on adult vaccination in India which makes comparing our findings with similar studies difficult. A 2018 US report on adult vaccination surveillance observed the coverage of the influenza vaccine to be around 46.1%, hepatitis B around 30%, and pneumococcal around 23.3%, which is significantly lower than the coverage of adult immunization in India [7]. The major reason for this could be the disparity in accessing vaccines in India, as adult vaccination is not covered in the routine universal immunization schedule.

The increase in antibiotic-resistant bacterial strains such as *S. pneumonia* [8] due to over-the-counter drugs has led to a rise in pneumococcal infections which may also invade the bloodstream, causing meningitis. Older adults are particularly at a higher risk of becoming severely ill and dying; hence, they must be vaccinated [8,9]. This could be the probable reason for the higher coverage of the pneumococcal vaccine among participants aged ≥61 years. Influenza caused by the influenza virus affects individuals of all ages but it has the highest risk of complications among older adults [8]. However, the effectiveness of the influenza vaccine is lower among older adults [10,11]. The WHO advises for an annual influenza immunization for older adults [8,12]. Our findings are consistent with the WHO's recommendations for vaccinating older adults; however, the coverage is considerably low which may pose a challenge for UHC [8]. Pneumococcal and influenza vaccines are indicated among diabetes patients since they have irregularities in immune function, leading to a rise in morbidity and mortality from infection [11,13]. Further, diabetics have a higher chance of complications from influenza and pneumococcal infections leading to hospitalization and death [11]. Diabetics have an appropriate humoral immune response to immunization [11]. Nonetheless, previous studies have reported that the influenza vaccine has reduced hospital admission during epidemics, whereas the pneumococcal vaccine

has been effective in reducing bacteremic infections [11]. Our findings show a very low coverage of both of these vaccines among diabetics which is a grave concern.

Typhoid fever continues to be an endemic disease in Southeast Asia with a substantial number of cases among teenagers and young adults [14]. Poor sanitation facilities, especially among deprived groups, is a major cause of typhoid [14,15]. However, we observed that deprived strata had a lower coverage of the typhoid vaccine which may lead to an increased case burden in this group. Additionally, both acute and chronic infections of hepatitis B cause disproportionately higher mortality and morbidity in LMICs, where it is a significant public health issue [16]. Evidence suggests catch-up immunization for younger adults is beneficial above costs [17]. Hence, for adults in India, catch-up immunization must be planned for those who were not vaccinated in their childhood. This should specifically be for the adults who are at a higher risk of infection such as drug abusers and individuals with liver diseases. Similar to the hepatitis B vaccine, the coverage of the DT vaccine during childhood is high but previous studies have reported unsatisfactory antibody levels among adults [18]. This highlights a need for adult DT vaccination [19]. It is to be noted that we found a low coverage of all vaccines which might lead to a high disease burden among adults.

We observed a variation in the coverage of various adult vaccines across wealth indexes. Participants belonging to the most affluent groups had the highest coverage of all vaccines. Our findings are consistent with the reports from other LMICs such as China, where a study observed that people living with a finance-reimbursed vaccination policy had a higher vaccination rate [20]. Moreover, a study conducted in Pakistan observed that the majority of the participants were not receiving adult vaccines due to lack of awareness [21]. A probable reason for this could be their ability to pay. Since we do not have a universal program for adult vaccination in India, individuals need to pay to receive the vaccines. However, the disparities across deprived and affluent groups may lead to a low coverage of vaccines which needs to be equitably dealt with. These findings are relevant with the conceptual framework of the Commission on Social Determinants of Health (CSDH) [22,23]. Additionally, our findings are consistent with the findings of a systematic review which investigated the role of social determinants and seasonal influenza vaccination in adults aged 65 years and above and found that age, gender, education, ethnicity, etc. influenced immunization [22]. Here, it is worth noting that older adults in India might need information, education, and communication (IEC) to take up vaccination as, conventionally, it is thought to be for children. Lack of awareness can be a major barrier in increasing immunization coverage which needs to be strengthened.

#### *4.1. Implications for Policy and Practice*

The National Technical Advisory Group on Immunization in India (NTAGI) does not provide a clear mandate on adult vaccination in India. However, their recommendations can shape the future course of adult immunization in India. Similar to COVID-19 vaccination, a phase-wise coverage based on the assessment of risk factors is required for all adult vaccines in India. Additionally, the provision of subsidized vaccines can also help in achieving higher immunization coverage. Along with the at-risk groups, women and economically deprived groups also need to be focused on. People living in hard-to-reach areas and tribal groups also are vulnerable to VPDs; hence, they require support for vaccination. The Ayushman Bharat scheme should establish adult vaccination in the bundle of services for the deprived class. Systematic mechanisms to vaccinate individuals with chronic conditions and multimorbidity is required. For equitable and egalitarian access, the availability of vaccines should be at the nearest healthcare centers. Furthermore, IEC and behavioral change communication (BCC) are required for beneficiaries to understand the need for vaccines. Adult immunization should be included in mainstream medical education and training curricula. Future studies on operational feasibility and enablers and barriers to adult immunization need to be explored.
