Factors such as health behaviors, opportunities to benefit from healthcare services, genetic structures and social structuring increase the tendency of individuals to develop healthy lifestyle behaviors. In this sense, immunization, one of the preventive, and promoting healthcare services, is of prime importance. Vaccines are one of the most important tools that contribute to the lifelong health protection and promotion of individuals and affect, especially the social dimension (Biasio et al., 2021). They reduce disease-induced disability and death, prevent epidemics, and offer a holistic approach to the health system (Demir Uslu et al., 2021). Vaccination services do not target herd immunity but are provided only at the individual level so that individuals can be protected somehow, nevertheless, the spread of vaccine-preventable diseases cannot be prevented. The mortality rate of vaccine-preventable diseases is at least two hundred times greater for adults than for children. More than 50.000 people die each year due to vaccine-preventable diseases (Sarıgül et al., 2021). The World Health Organization recommends vaccination for all individuals regardless of who they are, how old they are, or where they live (Toprak et al., 2018). Even though adult vaccines are easily accessible, vaccination rates for adults have not reached the desired level. In a study conducted in Turkey, adult vaccination rates were reported as 9.1 % for influenza, 22.8 % for tetanus, and 4.1 % for hepatitis B (Toprak et al., 2018). The pandemic has highlighted this picture even further (Dinleyici et al., 2020).

The coronavirus disease-2019 (COVID-19) has still been a global threat to humanity, which has presented experts, policymakers, and governments with various problems that go far beyond the health and well-being outcomes (Frenck et al., 2021). The COVID-19 pandemic, which has also influenced life-saving immunization services in low- and middle-income countries and even in developed countries, has caused people of all ages to be faced with the risk of death due to vaccine-preventable diseases. During the quarantine period of the pandemic, numerous countries have had to interrupt some mass vaccination campaigns like measles, diphtheria, meningitis, and poliomyelitis to prevent the risk of infection; however, 80 million children have been negatively affected by the lack of these immunization services (WHO, 2020). Arguments on the reliability and need for COVID-19 vaccine rapidly increased on printed and social media thus leading to vaccine hesitancy and refusal all around the world including Turkey (Wilson & Wiysonge, 2020). Individuals' vaccine attitudes and beliefs may in turn affect their attitudes toward adult immunization and thus the COVID-19 vaccine. According to the studies, some people have not been vaccinated against COVID-19 and other diseases, and they have also refused to allow their children to be vaccinated (Aygun & Tortop, 2020; Ikişik et al., 2022). During pandemics such as COVID-19, the media may broadcast misinformation about the virus's true effects, how treatment will be administered, and how vaccine research is progressing, encouraging people to trust such information (Aydın, 2020). Unfortunately, vaccine hesitancy, especially against the COVID-19 vaccine, has become a serious global issue due to the increasing effect of anti-vaccine movements (WHO, 2022; Feleszka et al., 2021; WHO, 2019; Ikişik et al., 2022).

The underlying causes of vaccination hesitancy are complicated and include more than a lack of information. Providing evidence to people who are doubtful is important, but it will not be sufficient to change the minds of those who are opposed to vaccination or have reservations about it. As a result, communication about vaccines should be planned and implemented with people's vaccine literacy in mind. Because vaccine information is sometimes complex, understanding it takes a certain degree of reading and numerical skills, making it challenging for young adults with limited health literacy to comprehend the information (Rowlands, 2014). Also, critical and appraisal skills are required to search for accurate information (Paul et al., 2021). In such a scenario, health literacy, and in particular vaccine literacy, should be considered as potential determinants of vaccine hesitancy, as it may affect vaccine uptake (Biasio, 2017). Vaccine literacy is a basic health literacy that is urgently needed to address the COVID-19 pandemic. Vaccine literacy occurs when people's skills and abilities are aligned with the content, processes, and systems required for vaccination. Vaccine literacy refers to one's ability to figure out, obtain and process basic health information, in order to make sound decisions about vaccinations (Ratzan, 2011). How individuals adhere to the pandemic measures is another important factor in increasing vaccination rates during this period. For this reason, individuals' perceptions on pandemic and their attitudes toward the fight against of the pandemic are important. Knowing these perceptions and attitudes by health authorities will guide them in both managing and fighting against the pandemic (Geniş et al., 2020).

The data of the WHO and the Turkish Ministry of Health show that those in the age group of 18–25 years are not accepted as a group at risk for developing a severe disease during the pandemic (T.C Sağlik Bakanlığı, 2021; WHO, 2020). The 18–25 age range is defined as adulthood, during which individuals face several hardships and decisions in their lives, such as seeking identity and changing their worldviews (Larson et al., 2015). In this sense, it is essential to know the views of people in this age group as they prepare the way for their decisions on their own health and the health of their children during this period. Health services in a society succeed only if individuals in that society give their full support to and participate in those services. When studies are examined, it has been emphasized that while vaccine-preventable diseases are decreasing in children, they are more common in adolescents and adults (WHO, 2020; Williams et al., 2017; Wilson & Wiysonge, 2020). It was also stated that adult vaccination rates are low in Turkey (Leidner et al., 2020; Tan, 2015). But, in addition to the effect of university education on adult immunization, it has been observed that no study has been found in which adult vaccine knowledge, attitudes toward the COVID-19 vaccine, and the level of COVID-19 vaccine literacy were evaluated together. Therefore, the aim of this study is to examine students' knowledge and attitudes about adult immunization and COVID-19 vaccine-related factors and to contribute to both national and international literature.