The COVID-19 situation has improved due to high vaccination coverage ( Dye, 2022). Unfortunately, virus mutagenicity produces new variants known to reduce vaccine effectiveness. Boosters have been provided to maintain the protective effect of the vaccine. Even though many researchers continue to develop new vaccines with high efficacy, doubts regarding their effectiveness and safety remain an issue ( Shukla et al., 2022).

Several studies have shown a relationship between sociodemographic and physiological factors and vaccine acceptance. The sociodemographic factors include age, type of occupation, marital status and monthly income ( Faturohman et al., 2021). Moreover, psychological factors might affect vaccination acceptance, adherence and completion ( Pandolfo et al., 2022; Yanto et al., 2021). Moreover, misinformation about the COVID-19 pandemic, including the therapy and vaccination, constitutes a huge challenge to overcome ( d'Arqom et al., 2021; Pristiyono et al., 2021).

In Indonesia itself, the current president, Joko Widodo, became the first Indonesian to become vaccinated on January 13, 2021. Since then, the Indonesian government has implemented vaccination programs for certain Indonesian population groups such as Indonesia’s medical personnel and the elderly. When this study was conducted, the vaccination for the general Indonesian adult population had just started, following the vaccination for healthcare professionals, the elderly, and individuals with comorbidity ( Jiao & Aditya, 2021).

However, various concerns have risen from the general population regarding the vaccine. Among these are views towards the vaccine’s effectiveness, its lack of research, misinformation about its side effects, religious beliefs, fear of injection etc. ( Fakhriani et al., 2022; Hidayana et al., 2022; Simanjorang et al., 2022; Theodorea et al., 2021). The Indonesian government ordered the vaccine from China and approved the emergency use for mass vaccinations; unfortunately, due to the concern above, vaccine acceptance was only about 64.8% as reported by UNICEF, WHO, and ministry of health ( UNICEF et al., 2020). In the end, to increase vaccine coverage, the Indonesian government made COVID-19 vaccination a requirement for all social aspects such as transportation, direct cash assistance programs (bantuan langsung tunai), obtaining passports, and other public services ( Gunawan J et al., 2022). This strategy remains in effect. With this mandate, vaccine acceptance increased from 60 to 86.81% ( Kemenkes, 2022). However, the debate on mandatory vaccines involves human rights issues ( King et al., 2022).

As Java is the most developed island in Indonesia and the most populated, most government facilities and programs are concentrated in this area, including the COVID-19 vaccination programs during the early implementation. Therefore, this study focused on an adult population in Java ( Arifin & Anas, 2021). Moreover, knowledge and awareness are part of individual factors affecting vaccine acceptance ( Erchick et al., 2022). Thus, this study aimed to measure the effect of COVID-19 vaccine knowledge and COVID-19 acceptance among Indonesian adults in Java during the first implementation of the COVID-19 vaccination mandatory programs.

Java island is the densest and the most developed island in Indonesia. The capital city of Indonesia is located in the west part of this island. The infrastructure, including transportation and health-related structure, is most complete and advanced compared to other islands in this country ( Handayani & Kumalasari, 2015). As the densest island, Java also contributes 68% of the COVID-19 cases in Indonesia. Therefore, the vaccination program was started on this island with the fastest spreading of the vaccination ( Arifin & Anas, 2021).

This study found that most of the respondents have a knowledge about the program, or at least have ever heard about the COVID-19 vaccination program. Only small portion of the respondents had never heard about it. Most of the respondents understand about the benefit and side effects of vaccination, from mild to severe cases. The positive determinant factors of COVID-19 vaccine understanding were respondents with young age and had medical background. Respondents that can be defined as having or did not have relatives with COVID-19, rather than did not know, had higher odds of having good self-claimed knowledge about this vaccine. Moreover, respondents received information from social media, webinars, and literature or journal. Meanwhile respondents with a lower level of education and lower self-reported economic status were less likely to have a good self-claimed knowledge about this government mass program. A similar finding was reported from 449 university students in Bangladesh that concluded medical students had higher odd of having positive knowledge about vaccines, as well as students majoring in economic and business, and science and technology ( Rahman et al., 2022). However, our study did not break down the medical-related field background, such as clinical doctors, medical lecturers, pharmacist, nurses, etc. as a study in Vietnam reported that the last two professions had lower knowledge about the COVID-19 vaccine ( Duong et al., 2022). Our findings also support that low income and education were related to low levels of knowledge, as reported in 1708 adults in Vietnam. However, in term of young age, this current study showed better self-claimed knowledge than a study in Vietnam ( Duong et al., 2022). A study in 1009 Turkey adults also found that respondents with bachelor degrees were more likely to have good knowledge regarding COVID-19 vaccination ( Sonmezer et al., 2022).

Even though during COVID-19 pandemic, social media was criticized due to its circulation about the misinformation, including on vaccine, in our study, respondents who got information form social media had higher odd to have good knowledge on COVID-19 vaccination, as well as for them who received information from webinar and literature/journal, compared to news, information from friend/family, etc. We cannot find the study that showed the source of information as a positive predictor factor on COVID-19 vaccine knowledge, but half of the respondents in Turkey, that concluded 62.7% have positive perceptions, used social media as their source of information regarding the COVID-19 vaccine ( Sonmezer et al., 2022). However, a study in 233 university students in Nigeria reported only 20.6% had a good knowledge on COVID-19 vaccination, and 60% of the respondent received information from social media ( Orok et al., 2022). This discrepancy might be caused by our study using self-claimed knowledge, instead of measuring it.

It has been reported that a good knowledge or understanding of vaccination is important for a successful vaccination program, such as in the influenza vaccine ( Yaqub et al., 2014), including in the COVID-19 vaccine ( Al-kafarna et al., 2022; Yupari-Azabache et al., 2022). As this study was conducted at the beginning of the vaccination program for general adults; therefore, the experience of COVID-19 vaccination was divided into six categories, including waiting list and hesitated. Our study showed that 60-70% of respondents had already received at least one vaccine and registered on a waiting list. Due to the limited stock of vaccine numbers, cold chain storage, vaccinator, etc., the vaccination program was faster in urban areas than in rural areas, even in Java ( Arifin & Anas, 2021). The public sentiment about the vaccine used in Indonesian COVID-19 vaccination program on its early implementation has become a challenge for the government ( Xu et al., 2022). Data from Twitter mining showed that 56% of Indonesian had negative tweet in January 2021 ( Pristiyono et al., 2021). Lack of confidence about vaccine efficacy, safety, and various personal reason was major concern found in this study. The acceptance options were further minimized in the multivariate analysis as reject, hesitate, and accept (consisted of respondents had received at least one jab and on the waiting list). Our study found a young adult and middle age adult respondents were less likely to accept the vaccination, as well as respondents that never heard, ever heard, and had a little knowledge about this vaccination. Almost half of younger respondents (18-25 years old) were still hesitant to receive COVID-19 vaccination, even though they claimed to have a good or enough knowledge about the vaccine. A similar finding was also reported in a study of 6,226 Palestinian adults, with 37.8% of them did not believe in the efficacy of COVID-19 as protection toward SARS-CoV-2 infection, even though younger Palestinians showed higher knowledge ( Al-kafarna et al., 2022). Our study also found that middle age respondents also have lower odd accept the vaccination. Their rejection and hesitancy was more likely due to their possibility to develop comorbidity diseases ( Fan et al., 2021) and higher risk to develop adverse event ( Almufty et al., 2021; Orebi et al., 2022). Our study also supports that less knowledge about COVID-19 vaccine also significantly associated with lower COVID-19 acceptance. A similar finding was also reported in Vietnam, where individual with less knowledge is more likely to reject COVID-19 vaccination ( Duong et al., 2022). The only significant positive predictor factor was having medical background, which might be related that the healthcare professionals were among the priority to receive the vaccination, and more likely due to higher level of knowledge as reported in Bangladesh and Vietnam ( Duong et al., 2022; Rahman et al., 2022).

As this study only covers one most developed and densest islands in Indonesia, a study with wider coverage is necessary. Moreover, as this study was conducted in the beginning of the vaccination program, a follow-up about the reason behind high vaccination coverage in Indonesia should be investigated and analysed as a lesson for future recommendations. Measurement of knowledge, instead of self-claimed, might show more complete picture, even though the results in this study mostly have similar finding with other studies.

Taken together, this study showed high COVID-19 vaccine knowledge and acceptance among adults on Java Island. Increasing understanding or knowledge about COVID-19 vaccine risks and benefits is necessary to reduce vaccination hesitancy. Vigorous campaigns and dissemination of information are needed to increase knowledge of young adults, people at high risk, low economic background, low education level and individuals with the nonmedical-related background. Moreover, because social media constitutes the highest source of information, it could be used for stakeholders to share the correct information about the pandemic and its vaccination programs, including booster programs.