Introduction
The 2019 coronavirus pandemic is emerging as a threat to public health [1]. COVID-19, which is considered a global emergency by the World Health Organization (WHO), was discovered in the Chinese city of Wuhan in late 2019 and quickly spread throughout the world [2]; As of October 2021, it has affected 244385444 people and caused 4961489 deaths worldwide. Iran has also reported 1008885 cases and 125716 deaths to date [3].
According to the report of the Centers for Disease Control and Prevention (CDC), the incubation period of this unknown disease is approximately two weeks [4]. The most common symptoms of this disease in the first 2-14 days include fever, fatigue, dry cough, myalgia, and shortness of breath [5]. In the absence of an effective treatment or vaccine, the best way to control infection was early detection, reporting, and isolation of people [6]. However, apart from effective public health measures, effective vaccination is necessary to limit this epidemic and also reduce its mortality [7]. In this regard, due to the production of numerous vaccines worldwide, the success of vaccination relies on its public acceptance [8]. But in recent years, public confidence in vaccines has been decreasing [9]. For example, when the H1N1 influenza virus vaccine was introduced, its acceptance rate was reported between 8% and 67% [10]. In the United States, an acceptance rate of 64% was reported [11] and in the United Kingdom, 56.1% of the studied participants accepted the flu vaccine [12].
Factors affecting the acceptance of the COVID vaccine may be as important as the discovery of the vaccine itself [13]. Studies on the acceptance of the COVID-19 vaccine showed that its acceptance varies depending on demographic factors, such as race, education level, as well as attitudes and beliefs about COVID-19 infection and vaccination [14, 15]. The official statistics of the Ministry of Health show that two months after the start of general vaccination, 30% of the groups that called for vaccination did not go to the vaccination centers against COVID-19 [16]. Studies on the acceptance of the COVID-19 vaccine showed that the acceptance of the vaccine varies depending on demographic factors, such as race, level of education, as well as people’s attitudes and beliefs about the disease and vaccination of COVID-19 [15, 17]. Halpin’s study in Ireland found that health workers avoided seasonal influenza vaccination due to misperceptions of efficacy and also a lack of confidence in the vaccine [18]. In China, demographic factors as well as people’s general perceptions were predictors of vaccination acceptance [19]. In Hong Kong, anxiety level and previous vaccination history were considered the most important reasons for vaccine acceptance [20].
Although Iran is one of the countries that has declared the highest agreement with the importance of the vaccine [9], the rate of acceptance of the COVID-19 vaccination is much lower than expected by the WHO [21]. As a result, many factors can affect people’s willingness to accept the vaccine; therefore, determining these factors in people who have accepted the COVID-19 vaccine or people who have not accepted the COVID-19 vaccine can provide useful information to resolve some ambiguities and obstacles created around vaccination. Therefore, the current study was conducted to reveal the factors that determine the acceptance of the COVID-19 vaccine in Gonabad.
Materials and Methods
The current study is a descriptive-analytical study that was conducted from June to July 2021 on 605 people using comprehensive health service centers in Gonabad.
Based on previous similar studies [8], taking into account the 60% rate of vaccination acceptance at the first type error level of α=0.05 and the test power of 80%, as well as the accuracy of 0.08, a sample size of 257 people, was calculated using the sample size estimation formula based on ratio estimation. Considering the possible loss of samples, the final sample size was estimated at least 275 people in each group, which can reach up to 330 people. Due to the similarity of the two populations (vaccinated and unvaccinated), the final sample size was considered double (Equation 1).


The inclusion criteria in the two studied groups were as follows: Membership in the integrated health system (SIB), the age of over 18 years, speaking in Persian and having the ability to communicate verbally, living in Gonabad at the time of the study, and no history of confirmed psychological disorders as stated by participants. In the vaccinated group, the person’s history of vaccination (at least once based on having a vaccination card) was also considered as one of the inclusion criteria. Also, the exclusion criteria in the two groups included failure to complete the questionnaire, with the difference that in the vaccinated group, unwillingness to inoculate subsequent doses of the vaccine was also considered an exclusion criterion.
The data collection tools in this study included a demographic information questionnaire, a researcher-made checklist assessing the reasons for vaccination by vaccinated people, and a researcher-made checklist assessing the reasons for the rejection of vaccination by unvaccinated people.
Demographic information checklist: The demographic information checklist included information related to age, sex, marital status, education, occupation, place of residence, history of underlying disease, history of smoking, history of COVID-19 vaccination, type of vaccine (in the vaccinated group), history of being infected with COVID-19, and a history of hospitalization due to COVID-19.
The researcher-made questionnaire on the reasons for vaccination of vaccinated people: This checklist, which was developed according to previous studies [22, 23, 24, 25] and also the opinions of experts, included eight items in the form of three main categories, including social factors (two items), individual factors (three items) and compulsions (three items). Also, an option titled “Other reasons” was added for people to state reasons that were not on the checklist. In this tool, vaccinated people could choose from one to eight cases as reasons for getting vaccinated.
The researcher-made questionnaire on the reasons for non-vaccination of unvaccinated people: This checklist is also based on previous studies [22, 23, 24, 25] and experts’ opinions designed with 21 items in the form of three main categories, including social factors (three items), individual factors (ten items), and factors related to vaccination (eight items). Individual factors were divided into two subscales: personal belief (three items) and lack of knowledge (seven items). Also, an option titled “Other reasons” was added for people to state reasons that were not included in the checklist. In this tool, unvaccinated people could choose from 1 to 21 cases as reasons for getting vaccinated. It should be mentioned that for the content validity, after determining the items of the questionnaire, it was sent to eight members of the academic staff in nursing groups in the specialties of geriatric nursing, gerontology and community health nursing, and university health in the specialties of epidemiology and health education and health promotion. The experts were requested to evaluate the questionnaire according to the subject of the study and express their opinions and suggestions. After collecting opinions and suggestions, the final questionnaire was prepared with the agreement of the research team. The reliability of the questionnaires was obtained using Cronbach’s alpha coefficient of 0.74 for the checklist on the reasons for vaccination in vaccinated people and 0.89 for the checklist on the reasons for not vaccinating in unvaccinated people.
The sampling method in this study was multi-stage. First, three health centers of comprehensive health services in Gonabad city were considered as clusters, and eligible people were selected from each cluster and divided into vaccinated and unvaccinated groups according to vaccination history. Individuals from each group were selected randomly and contacted (due to the possibility of contagion and spread of the disease). During the introduction, the researcher gave necessary explanations of the objectives of the project and the confidentiality of the participants’ information and obtained their verbal consent. Then, depending on whether they were vaccinated or not and the demographic profile questionnaire, a checklist of “Reasons for vaccination” or “Reasons for non-vaccination” was completed in the form of a telephone interview. 
After data collection, the analysis was done using SPSS software, version 23. Descriptive statistics (frequency determination, dispersion determination, and central tendency index determination) were used to analyze the data, and the Chi-square inferential test was used to check the homogeneity of the studied variables.
Results
In this study, information about 605 people living in Gonabad city was analyzed in the form of two vaccinated (302 people) and non-vaccinated (303 people) groups, of whom 307 were men (50.7%) and 298 were women (49.3%). According to the time of conducting this study, most of the people participating in this research were 60 years old and older (69.9%). The Mean±SD age of the participants in the vaccinated group was 57.55±12.24 years and in the non-vaccinated group, it was 55.83±14.78 years. The frequency of participants’ age is reported in Table 1.


Most of the research subjects were retired (45%) and had a diploma (26.6%). Also, among the vaccinated people, the most type of inoculated vaccine was Sinopharm (73.5%). Many other demographic characteristics of the research subjects are reported in Table 2.


The results of the statistical tests also showed that the two studied groups were very similar in terms of the examined variables (P>0.05), indicating that the study subjects were chosen randomly.
The results of the study on the reasons for accepting vaccination in the vaccinated residents of Gonabad showed that job compulsion (16.5%) was the most frequent reason among the compulsions, being tired of quarantine conditions (73.7%) as the most frequent reason related to individual factors, and living with high-risk people (5.88%) was the most frequent reason related to social factors. The frequency of other reasons for accepting vaccination for each factor is listed in Table 3.


The results of the study on the reasons for not accepting vaccination in non-vaccinated residents of Gonabad showed that the fear of complications caused by the vaccine in the individual (63%) was the most frequent reason among factors related to vaccination, the coercion of people around them not to get vaccinated (26.2%) was the most frequent reason related to social factors, and concern about the content of the vaccine and lack of knowledge of its effectiveness (3.45%) was the most frequent reason among individual factors. Table 4 shows the frequency of other reasons for not accepting vaccination by sub-scales.


Discussion
This study aimed to determine the factors related to the acceptance and non-acceptance of the COVID-19 vaccine among the residents of Gonabad city in 2021. The results of the study showed that factors, such as living with high-risk people, being tired of quarantine conditions, and job pressure are reasons for accepting the vaccination of COVID-19 in vaccinated people.
The results indicated that the most important factors related to the acceptance of the COVID-19 vaccination are social factors. Kashmiri et al. also considered social support as the most important factor influencing the acceptance of vaccination [8] because social support through providing information to people, encouraging them to get vaccinated, and also providing convenient access to the vaccine can improve vaccine acceptance [8]. The results of this research showed that 80.9% of the vaccinated residents put forward the observance of the rights of others by being vaccinated as one of the reasons for accepting the COVID-19 vaccination. Similar to Bell’s study, vaccination to protect oneself and others was the most common reason for accepting the COVID-19 vaccine. Machida et al. also stated that 54.77% of the researched population had a high desire to protect others with their vaccination [1]. This statistic was reported to be nearly 65.5% in another study that investigated people’s attitudes toward the COVID-19 vaccination [26]. In this study, being tired of the quarantine conditions, with a frequency of 7.73%, was expressed as another important factor in accepting vaccination. This shows that people who accepted the conditions of quarantine and social distancing were more willing to get vaccinated. Edward et al. also stated that people who observed higher levels of behaviors, such as social distancing had less resistance to accepting the COVID-19 vaccination [27].
The results of the present study showed that factors, such as fear of side effects caused by the vaccine, concern about the content of the vaccine, and lack of knowledge of its effectiveness, as well as the coercion of others not to get vaccinated, are related to the non-acceptance of COVID-19 vaccination. In this regard, 63% of the participants said that they refuse to inject a vaccine due to the fear of possible side effects of the vaccine. Gadoth et al. showed that 35% of health workers are worried about the side effects of the COVID-19 vaccine [28]. Qattan et al. reported that 26.73% of the people refused to inject the vaccine due to fear of adverse side effects [29]. This statistic is lower than the results obtained in the present study, which can be due to the greater frequency of elderly people in the present study (47%) compared to the mentioned study (3.57%). It seems that due to the changes caused by aging, co-morbidities, and also greater vulnerability to immune risks [30], they refused to get vaccinated against COVID-19. 
The present study showed that 4.6% of the participants refused to inject the vaccine due to insufficient knowledge about the COVID-19 vaccine. A study conducted on health workers also showed that the lack of transparency and information available to the public about a vaccine is considered the main reason for the reluctance to inject vaccination [28]. Also, Bell et al. stated that 4.8% of the participants are not willing to be vaccinated due to the lack of information about the vaccine [17]. The results of the present study also showed that nearly 3.45% of the concern of the subjects was due to a lack of knowledge about the content and efficacy of the vaccine, which can be a reason for people’s lack of trust in vaccination. This means that to convince communities to accept vaccination, strong reasons and evidence about the safety and effectiveness of the vaccine are needed. For example, Mannan et al. stated that 42.6% of the participants had a positive attitude regarding the lack of trust in the benefits of the COVID-19 vaccine [26]. This statistic was very close to the statistics obtained from the present study. The results of the study showed that 0.6% of the participants do not believe in the existence of COVID-19. Qattan et al. also showed that 0.6% of participants did not believe in the existence of COVID-19 [29]. This statistic is very close to the statistics obtained from the present study. This research also showed that nearly 4% of participants refuse to get vaccinated because they have been infected with COVID-19 in the past. At the same time, the results of Bell et al. also stated that only 6% of the people participating in the research avoid the injection of the vaccine due to being infected with COVID-19 [17]. Also, nearly 3.4% of the participants mentioned a lack of belief in vaccination as a reason for not injecting the vaccine. Meanwhile, 91.6% of participants in a study conducted on Saudi health workers stated that masks and disinfectants are sufficient to protect against COVID-19 [29]. This statistic is almost similar to the statistics of the present study.
Conclusion 
Considering that getting rid of the COVID-19 epidemic requires maximum vaccination coverage for all members of society, and in this research, the fear of complications and concern about the content and ineffectiveness of the vaccine are among the main factors for rejecting the COVID-19 vaccination, increasing the awareness and knowledge of the public about the effectiveness of vaccines available in the country through reliable sources and also efforts to reduce the fear of its side effects require planning and investment at the macro level in the country. Also, measures to increase people’s willingness to protect others by their vaccination, such as increasing people’s correct information through networks and social media may be the key to promoting the acceptance of the COVID-19 vaccination. These results may be useful in planning educational activities to increase the acceptance of the COVID-19 vaccine as well as to address the factors of non-acceptance of the COVID-19 vaccine.
This study had strengths and limitations. Based on the studies conducted, as far as we know, the present study is the first study that investigated the factors related to the acceptance and non-acceptance of COVID-19 vaccination in Iranian society. Using the cluster sampling method enabled the researchers to examine people from all areas of Gonabad city. However, conducting this research was accompanied by limitations. Among the limitations of the current research is using a questionnaire completed using the phone, which deprived the researchers of the possibility of face-to-face and effective communication. In addition, some people hung up the phone while completing the questionnaire due to fatigue or other issues that were not visible to the researcher. Another limitation of the study was the self-reporting of the subjects to answer the questions in the questionnaire and some of them, despite emphasizing the confidentiality of the answers, refused to provide the real answer or avoided answering the questions correctly for some reason. Finally, because the factors of acceptance of COVID-19 vaccination may be different in each region, it is suggested that another study be conducted to investigate the factors related to the acceptance of COVID-19 vaccination in a wider population (for example, in Iran). 

Ethical Considerations
Compliance with ethical guidelines
To comply with all ethical issues, permission to conduct the research was obtained from the Deputy of Research and Technology of Gonabad University of Medical Sciences and Code of Ethics under reference number IR.GMU.REC.1400.039. Informed consent for the participants was verbal and in the form of an agreement to participate and continue the study. They were also assured about the confidentiality of their information.

Funding
This research was done with the financial support of the Gonabad University of Medical Sciences.

Authors' contributions
Conceptualization and design of the main idea: Erfan Pourshahri; Methodology: Leila Sadegh Moghadam and Nasim Khajavian; Research and review: all authors; Writing the original version, editing, and finalizing the text: All authors.

Conflicts of interest
All authors declared no conflict of interest. 

Acknowledgements
Hereby, we would like to express our gratitude to the financial and moral support of the respected research vice-chancellor of Gonabad University of Medical Sciences, as well as to all the people who contributed to this study.


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