COVID-19 vaccines knowledge and acceptance among Indonesian adults in Java Island

Study design and data collection

This cross-sectional study on COVID-19 vaccination among Indonesian adults in Java during the second wave of the pandemic was part of the Dietary Supplement, COVID-19 Vaccine Acceptance, and Mental Health among Indonesian Adults project. This study followed the Helsinki Declaration and was approved by the Health Research Ethics Committee, Faculty of Medicine, Universitas Airlangga (No. 86/EC/KEPK/FKUA/2021). The data were collected from March to June 2021 using a web-based survey generator (www.surveyplanet.com). The survey was distributed online on social media and via email. Before entering the survey, respondents were provided with a landing page consisting of the objective of the study, brief explanation of the survey, the responsible person, and an informed consent page containing permission to use the data anonymously. The respondents provided their consent by choosing the YES button. Multiple submission was prevented by the web-based generator. The inclusion criteria of the respondents were Indonesian citizen, older than 18 years old, and residing in Java when the study was conducted. The minimum sample size was 383, calculated with 5% margin of error, 95% confidence level, and unknown population number which filled with 100,000. This study followed the Checklist for Reporting Results of Internet E-Surveys (CHERRIES) guidelines, and the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines (Eysenbach, 2004; Vandenbroucke et al., 2007).

Survey instrument

Three sections of the questionnaire were developed and distributed online to measure respondents’ COVID-19 knowledge and acceptance. The sections covered sociodemographic information of the respondents, their knowledge of COVID-19 vaccine effects and their acceptance of COVID-19 vaccination. The sections of vaccine knowledge were modified from a questionnaire from UNICEF (UNICEF et al., 2020) and the COVID-19 vaccine acceptance behaviours were developed by a medical doctor and evaluated by three experts, two pharmacologists and a social science expert. Face validity was performed concerning 20 respondents to ensure their understanding of the questions, including the wording and format. A copy of the questionnaire can be found in Extended data.

Analytical procedure

Respondents were divided into two groups based on their sex: male and female. COVID-19 vaccine general knowledge and vaccine acceptance behaviours were measured using nominal scales. Data were processed and analysed using Microsoft Excel and SPSS 24.0 (IBM, Chicago, IL, USA), and visualized using GraphPad Prism 5.0. Descriptive analysis for each categorical variable was measured, followed by the chi-square test to observe differences between groups. For analysis, we converted the occupation into unemployed and employed, and religion into majority and non-majority. Multivariate ordinal regression analysis was performed to determine determinant factors of self-claimed vaccine knowledge and acceptance. All models were mutually adjusted for all potential confounders, such as sex, age, marital status, employment status, economic status, education, religion, insurance, history of testing positive for COVID-19, as well as the history of family members or relatives testing positive for COVID-19. The dummy variables included sex, marital status, religion, medical background and employment status. Vaccine acceptance points were contracted into reject, hesitate, and accept (respondents who received at least one vaccine or on the waiting list). Significance was defined as a p-value <0.05.

Characteristics of respondents

The questionnaires recorded 1,006 responses from March to June 2021. Only 910 responses were valid after the exclusion criteria. The 96 responses were excluded due to domicile outside Java. From these 910 responses, the majority were female, most numerous in the 18 to 25-year-old age group, with marital status single or unmarried, and average economic status. The majority of female respondents were unemployed and had graduated from high school, while the majority of male respondents were employed and held a bachelor’s degree (p=0.000 and p=0.005, respectively). Table 1 summarizes respondent characteristics.

Experiences of COVID-19 and its vaccination

Most respondents reported never experiencing COVID-19 symptoms such as fever, sore throat, coughing, aches and pain, loss of taste and smell, etc. More female respondents reported these conditions compared with male respondents. Only 175 (19.2%) respondents reported that they ever experienced COVID-19 symptoms, with more male respondents confirmed to have symptoms compared with female respondents, both with or without lab confirmation (Figure 1A, p= 0.002). However, the proportion of the respondents did not differ regarding knowing relatives who contracted COVID-19 (Figure 1B).

Figure 1. History of COVID-19.

(A) History of contracting COVID-19, and (B) History of family/relatives testing positive for COVID-19.

All respondents have some knowledge regarding the vaccination programs being initiated by the government, with more male respondents reporting having good knowledge levels, and more female respondents reporting having sufficient knowledge about the vaccine (p= 0.040). Less than 1% of males and females confessed never hearing about the vaccination programs (Figure 2A). No difference was found concerning respondents’ knowledge on benefits of obtaining the COVID-19 vaccine, including preventing infection and spreading infection, preventing fatality from COVID-19, and even though they contract the disease, they will only exhibit mild symptoms (Figure 2B). Similar knowledge was also observed concerning the side effects of vaccination. The respondents knew that side effects ranged from mild to severe, from soreness at the injection site to anaphylactic shock (Figure 2C). They confessed that the main source of their information was social media, friends/family members, news and others (Figure 2D).

Figure 2. Self-claimed knowledge and understanding about the COVID-19 vaccine.

(A) Self-claimed knowledge of the respondents, (B) benefits of COVID-19 vaccination, (C) side effect of the COVID-19 vaccine and (D) source of information about COVID-19 vaccination programs.

When this study was conducted, COVID-19 vaccination remained limited for healthcare providers, the elderly, people with comorbidity and just reaching general adulthood. However, data of general adults were recorded and placed on a waiting list. Therefore, vaccine acceptance in this questionnaire was divided in six categories: received two shots, received one shot, received more than three shots, on a waiting list, hesitating, and rejecting the COVID-19 vaccine.

The majority of respondents were willing to accept COVID-19 vaccines, with more female respondents receiving two doses of the COVID-19 vaccine, and more male respondents on the waiting list. One-third of male respondents hesitated whether to receive a shoot or not during this study period, which was more than female respondents (25%). The rejection number was less than 10%, with a higher proportion comprising male respondents (Figure 3A). Among respondents who received the vaccination, the strongest reason to receive was its safety, followed by its possibility to reduce COVID-19 fatality (Figure 3B). The three major side effects experienced by respondents receiving vaccination were soreness at the injection site, drowsiness, and myalgia or body aches. Only one male respondent experienced an anaphylactic reaction, even though more than 1% of male and female respondents reported allergic reactions such as itchiness and swelling (Figure 3C). For those still hesitant to receive the COVID-19 vaccine, almost two-thirds would consult healthcare professionals and their family members or friends. Different patterns concerning to whom respondents would consult were observed in this study. In all, 5.3% of the female respondents considered consulting health cadres, which was higher than that of male respondents (3.77%). Moreover, a smaller portion of female respondents considered consulting a government officer or their teacher, while none of the male respondents considered it. Less than 2% of males and females would not consult anyone, except themselves (Figure 3D). Furthermore, the strongest reasons for not receiving the COVID-19 vaccine were fear of side effects, insufficient information about this program, and doubt concerning its effectiveness and safety (Figure 3E).

Figure 3. The acceptance and experiences concerning COVID-19 vaccination.

(A) Vaccine acceptance, (B) strongest reason to receive COVID-19 jabs, (C) side effects experienced after receiving the vaccine, (D) who hesitating respondents will consult about the programs and (E) reason for vaccine rejection.

Determinants of COVID-19 knowledge and acceptance

Ordinal regression was performed to predict sociodemographic factors associated with respondents’ COVID-19 knowledge and acceptance. Table 2 shows the results from modelling the outcome as a function of several independent variables including age, sex, marital status, work, economic status, education, religion, insurance, having a relative contract COVID-19, and testing positive for COVID-19. The model in Table 2 shows that young adults were 2.654 times and 2.071 times more likely to have a good knowledge on COVID-19 vaccinations than older subjects (18-25 year olds 95% CI 1.534 to 4.592, p=0.000; >25-35 year olds 95% CI 1.130 to 3.796, p= 0.018, respectively). Respondents with a medical background were 2.176 times more likely to possess knowledge of COVID-19 shots (95% CI 1.586 to 2.984, p=0.000). Another positive predictor factor was their knowledge about relatives that had or never had contracted respondents that did not know about this matter. Respondents that could defined that they had relatives who contracted with COVID-19, either yes or no, have higher knowledge about COVID-19 vaccine compared with respondents that did not know about this matter. Respondents that had relatives with COVID-19 were 1.902 more likely to have a good knowledge about COVID-19 vaccination programs (95% CI 1.239 to 2.920, p= 0.003), in contrast, respondents with no COVID-19 positive relatives were 1.583 time more likely to have knowledge about the vaccination (95% CI 1.014 to 2.471, p= 0.043). In addition, respondents following related information, through social media and webinars were more likely to have a higher knowledge level concerning COVID-19 compared with respondents receiving information from other sources (social media: AOR 2.456, 95% CI 1.180 to 5.112, p= 0.016; webinars: AOR 3.563, 95% CI 1.524 to 8.331, p= 0.003, respectively).

The negative predictors to knowledge COVID-19 vaccination programs were economic and education status. Respondents with lower economic status, below average and average, were less likely to have a good knowledge on COVID-19 vaccinations (below average: AOR 0.439, 95% CI 0.244 to 0.790, p= 0.006; average: AOR 0.438, 95% CI 0.278 to 0.689, p= 0.000). Similarly, respondents with lower education were also less likely to have a good knowledge on vaccinations as respondents below high school level education were 0.120 more likely to have a good knowledge about this program (95% CI 0.057 to 0.254, p=0.000) and high school graduates were 0.490 more likely to have a good knowledge about this program (95% CI 0.286 to 0.838, p=0.009).

Moreover, for COVID-19 vaccination acceptance, at this study period, young adults (18-35 years old) have higher odds to receive and to accept the vaccination (18-25 years old: AOR 0.071, 95% CI 0.031 to 0.159, p= 0.000; >25-35 years old: AOR 0.287, 95% CI 0.114 to 0.724, p= 0.008), as well as middle age adults (>45-55 years old: AOR 0.222, 95% CI 0.087 to 0.567, p= 0.002). Respondents with no or less knowledge about COVID-19 vaccination programs also less likely to receive the jab. Respondents that never heard about these programs were 0.035 times more likely to obtain a vaccination (95% CI 0.005 to 0.239, p=0.001), In contrast, respondents that only heard about government programs were 0.071 times more likely to receive the COVID-19 shot (95% CI 0.035 to 0.145, p=0.000). Respondents with little knowledge about vaccination programs were 0.455 times more likely to receive a jab (0.208 to 0.994, p= 0.048). The only significant positive predictor was whether the respondents had a medical background (AOR 1.488, 95% CI 1.019 to 2.175, p=0.040). The result of ordinal regression for COVID-19 vaccine acceptance was showed in Table 3.