Introduction

The Corona Virus Disease-2019 (COVID-19) had severe effects on health and wellbeing, economy, and healthcare delivery systems1,2. Vaccines against the disease became available by the end of 20203. Emergency use authorization was granted to two mRNA COVID-19 vaccines, the Pfizer-BioNTech and the Moderna COVID-19 vaccines and they protected against severe complications, reduced fatality rates, and deceased hospital admissions4,5. Millions of COVID-19 vaccine doses have been administered since December 2020. By 2021, it was clear that one dose of these vaccines would not provide adequate protection and that booster dose/s would be needed6. Several studies assessed booster dose acceptance and factors associated with intention to take boosters7. The percentage of persons willing to receive the COVID booster among the fully vaccinated was highest in Brazil (96%), Mexico (93%), China (90%), and lowest in Italy (66%) and Russia (62%)8. In the Middle East and North Africa (MENA), the intention to take the booster dose in different countries ranged from 45 to 78%9,10,11, and the overall estimate from several low and middle countries in the MENA region in another study was 26%7. Fear of complications and vaccine hesitancy were common among the populations in the region12.

Behaviour modification theories offer a framework to explain and address vaccination hesitancy. These theories include the health belief model (HBM) 7, the extended protection motivation theory 13, the theory of planned behaviour (TPB)14, and a combination of these theories15. According to the HBM, people engage in a preventive behaviour if they believe that they are vulnerable to a serious disease, that the disease can be prevented, and that they can manage the barriers against the preventive behaviour to prevent the disease15. On the other hand, the TPB15 explains the factors affecting the intention to adopt a behaviour and the intention, in turn, predicts behaviours. The TPB posits that intention depends on one’s attitude toward the behaviour, perceived control over the behaviour, and perceived norms regarding the behaviour. The HBM and the TPB provide a comprehensive framework to identify factors associated with vaccination16. Both theories explained Chinese parents’ decision to give a COVID-19 vaccine booster dose to their children and a study showed that attitude and behavioural control were significantly associated with parents’ intentions whereas subjective norms, perceived severity and susceptibility had no significant association with this intention17. Research also assessed the ability of constructs from the two theories to affect the uptake of the COVID-19 vaccine booster among adults in Italy and only subjective norms were directly associated with vaccination intention whereas perceived vulnerability and perceived disease severity were indirectly associated with vaccination intention through fear of COVID-1918. Thus, constructs from these two theories previously explained vaccine booster uptake in different settings and may, thus, be of value in explaining the same behaviour in Egypt.

In Egypt, there have been 516,023 confirmed cases of COVID-19 with 24,830 deaths until February 16th 202419. Egypt ranked 7th after China, USA, Brazil, India, Italy, and France in case fatality rate due to COVID-1920. Also, Egypt had one of the lowest administration rates of the first dose of the COVID-19 vaccine and its boosters21. The low uptake of the vaccine was due to concerns about safety and side effects22. However, Egypt is one of the few middle-income countries that were able to locally produce COVID-19 vaccines23 and this was assumed to increase vaccine availability and boosters’ administration. A study assessed the intention of using the COVID-19 vaccine booster in Egypt and reported that 60.2% of participants were willing to receive a booster dose and 20.4% were reluctant12. The primary reasons for refusing the booster dose were uncertainty about safety and considering that the booster dose was not necessary. However, this study shed no light on the determinants of the intention to take a booster dose12. Another study assessed the opinions regarding COVID-19 vaccines in Egypt in 2021 and reported that 81.4% of participants were afraid of the vaccines, especially females and residents of rural areas24. In 2022, The Ministry of Health in Egypt conducted a national survey to assess the perception of COVID-19 vaccination and reported that only 41.8% were fully vaccinated. The study attributed incomplete vaccination to administrative issues such as crowded health facilities and registration problems but the determinants of booster dose uptake were not addressed25. More recently, it was reported that 47% of participants, of whom 29.3% were healthcare providers, refused to be vaccinated26, while 69% of university students accepted COVID-19 vaccination out of fear of getting infected27.

The World Health Organization (WHO) ended the international emergency because of the COVID-19 pandemic28. However, the study of vaccination and uptake of booster doses offer insights about the factors affecting the spread of the pandemic that are critical for controlling future pandemics. The international community is striving to ensure that preparedness activities are ongoing, to mobilize resources, and establish processes to address future scenarios. Research continues about the intention to take COVID-19 vaccine boosters and its determinants29,30,31,32. It is important to assess the impact of various determinants on the intention to receive a booster dose to design interventions that promote the uptake of vaccines and their boosters. This study assessed the intention to receive COVID-19 vaccines booster doses among vaccinated persons in Egypt and to identify factors associated with this intention based on a comprehensive theoretical framework including the HBM and the TPB. The study hypothesized that there would be no association between intention to receive a COVID-19 vaccine booster and the constructs of the HBM or the TPB.

Methods

Design

We used a cross-sectional online survey to collect data from participants living in Egypt between March and June 2022. This period followed an announcement by the Egyptian government of plans to export the locally produced COVID-19 vaccine to neighbouring African countries33. Ethical approval was obtained from the Research Ethics Committee, at the Faculty of Dentistry, Alexandria University (#0397-02/2022). The study was conducted in full accordance with the Helsinki declaration.

Participants and sampling

We invited a convenience sample of people living in Egypt through social media and included participants if they were adults aged 18 years or older and had access to the survey through an electronic device and the internet. There were no exclusion criteria. Sample size was calculated using GPower to detect an odds ratio of at least 1.5 of intention to take the vaccine booster in relation to determinants in a two tailed test. We specified an alpha error = 5%, power = 80% with expected percentage of intention to take a booster dose = 60%9,34. To accommodate the independent variables with various distributions, the required sample size ranged from 215 to 844. Assuming non-response = 20%, 1013 ~ 1100 participants would be needed.

Study questionnaire

We collected data using an anonymous, close-ended questionnaire based on a previous study35. The questionnaire included three sections (Appendix 1). The first section assessed participants’ demographic profile including age in years, sex (male or female), background (university student or other), and residence (the governorate in which the participant lived). The second section assessed medical history including reported history of chronic diseases (yes or no), history of COVID-19 infection (yes or no), COVID-19 vaccination history (yes or no) and perceived health (on a 5-point Likert scale ranging from very bad, bad, average, good, to very good). The third section assessed opinions toward COVID-19 vaccines including awareness of a number of COVID-19 vaccines available in Egypt (Oxford AstraZeneca, Moderna, Pfizer BionTech, Sinovac, Sinopharm, Sputnik and others)36, knowing that COVID-19 vaccine is mandatory in Egypt (yes, no, do not know), agreeing that vaccines are harmful (on a 5-point Likert scale ranging from not at all, no, neutral, yes, to yes completely), agreeing that vaccines may lead to death (yes, no, do not know), and confidence in locally- and foreign-manufactured vaccines (on a 4-point Likert scale including not at all, no, yes, and yes completely). This section also asked about the percentage of persons in the participants’ own circle who were vaccinated (none to 25%, more than 25 to 50%, more than 50 to 75% and more than 75 to 100%) and whether the participants intended to take the COVID-19 vaccine booster (on a 4-point Likert scale including definitely no, maybe no, maybe yes and definitely yes).

The study team developed the questions and response items in simple language to avoid confusion and elicit accurate responses. Two bilingual researchers, fluent in Arabic and English, independently translated the original questionnaire from English then back-translated the Arabic version to English and compared the two English versions to assess differences and edited to ensure accuracy and appropriateness to the local context37. We assessed content validity by asking six healthcare providers to rate the relevance of the items in the different sections and calculated the content validity ratio (CVR). The CVR was 0.86 which was greater than the recommended value38. We further piloted the questionnaire with persons from the general population including seven visitors to the outpatient clinic in Alexandria University hospital and they indicated that the questionnaire had good flow, the questions were easy to understand, and the options covered all scenarios.

A researcher uploaded the survey to SurveyMonkey. The survey included an introduction explaining the study purpose and inviting people to participate after affirming the confidentiality of responses, emphasizing voluntary participation, describing that participants can withdraw at any time and inviting them to communicate with the principal investigator if they had questions. Respondents had to click on a button to indicate consent to participate and procced to the survey. Participants could make only one submission per electronic device to avoid duplicate answers. No IPs or emails were collected to ensure confidentiality. The survey took 10–15 min to answer. The participants received no incentives to answer the survey.

Data collection

The core team from Alexandria University reached out to researchers from various regions in Egypt to ensure geographic inclusion including the Delta, Upper Egypt, Suez Canal area, the Eastern area, the greater Cairo area, and Alexandria area. The extended study team members distributed the survey links to people in their networks using social media groups on Facebook, WhatsApp groups and Telegram for professionals, university students, and lay people. The survey links were posted in late March 2022 then reposted again in May then June to maximize response rates.

Analysis

Data were cleaned and imported to SPSS version 23.0 (IBM Corp., Armonk, N.Y., USA). Only complete responses were used for analysis. We categorized the place of residence into 5 areas39: (i) greater Cairo (Cairo, Giza and Qalyubia), (ii) Alexandria area (Alexandria, Beheira and Matruh), (iii) Delta area (Dakahlia, Kafr El Sheikh, Gharbia, Menoufia and Damietta), (iv) Suez Canal area (Port Said, Ismailia, Suez, Sharqia, North Sinai and South Sinai), and (v) Upper Egypt (Beni Suef, Minya, Faiyum, Asyut, New Valley, Sohag, Qena, Luxor, Aswan and the Red Sea). We calculated the score for awareness of types of vaccines by adding the number of vaccine types the participants identified, ranging from zero (not aware of any type) to 7 (aware of all types). We selected the participants answering “yes” to the question about the history of COVID-19 vaccination for multiple binary logistic regression analysis.

Estimation model

The dependent variable was “intention to take a COVID-19 booster”, categorized into yes (definitely yes and maybe yes) and no (definitely no and maybe no). The independent variables were indicators of the HBM constructs: perceived susceptibility to COVID-19 infection including “history of chronic disease”, “perceived health” and “history of COVID-19 infection” and possibility of preventing the disease including “score of awareness of types of COVID-19 vaccines available in Egypt”. The third construct in the HBM, ability to address barriers to the health behaviour (booster uptake), was conceptualized as increased vaccine availability through local manufacture which applied at country level and, thus, we did not include it in the regression model since all participants were exposed to it. The indicators of the TPB constructs were attitude toward COVID-19 vaccines including “agreeing that vaccines were harmful”, “that they may lead to death” and “confidence in vaccines, local and foreign”; perceived norms including “percentage of vaccinated persons in the participant’s circle” and perceived control over the behaviour including “knowing about the presence of government mandates to be vaccinated against COVID-19”.

The confounders were socioeconomic indicators including “age”, “sex”, “background”, “place of residence” and “time in days since the beginning of the survey” as a quantitative variable because the survey was open for several months. The independent variables were introduced individually in a series of unadjusted models then together in a multiple adjusted model. We calculated the unadjusted and adjusted odds ratios (UORs and AORs), 95% confidence intervals (95% CIs) and p values as well as the unadjusted and adjusted estimated marginal effects of the logit model and displayed them for all subgroups and also included them in Appendix 2 for the full model. Significance level was set at 5%.

Results

The study included 1113 complete responses out of 1401 collected responses (79.4%). Table 1 shows that the average (SD) age of participants was 25 (9.5) years, 66.7% (n = 742) were females, and 68.6% (n = 764) were university students. The greatest percentage of participants were from Alexandria region (31.9%; n = 355). Most participants had no chronic diseases, no history of COVID-19 infection and good/ very good perceived health. On average, they were aware of 3.7 types of COVID-19 vaccines available in Egypt out of 7 and indicated that COVID-19 vaccines were mandatory in Egypt (64.4%; n = 717). Also, 16% (n = 178) thought that vaccines may lead to death. A total of 43.4% had confidence or complete confidence in locally manufactured vaccines and 67.3% had confidence in foreign manufactured vaccines. Also, 76% thought that more than 50% of the people in their circle were vaccinated against COVID-19. In total, 70.6% (n = 785) expressed an intention to take the COVID-19 vaccine booster dose. Those who had already taken the COVID-19 vaccine were 1064 (95.6%) and regression analysis was restricted to them. No statistically significant differences existed between the whole sample and vaccinated persons in all factors (P > 0.05).

Table 1 Socioeconomic background, medical history, awareness, attitude toward vaccine, percentage of vaccinated acquaintances and intention to take COVID-19 vaccine booster dose.
Full size table

Table 2 shows that in unadjusted analysis, intention to take a booster dose of the COVID-19 vaccine was significantly associated with history of COVID-19 infection where participants with a history of COVID-19 infection had 31% higher odds of intending to use a booster dose than those without a history (P = 0.049). Not thinking that vaccine may lead to death was associated with 59% higher odds of intending to use a booster dose (P = 0.002) whereas not knowing whether vaccines lead to death was associated with 46% lower odds of intending to use a booster dose than thinking that vaccines lead to death. Agreeing that vaccines were not harmful at all, not harmful or being neutral about their harm was associated with 6.48% to 30.75% higher odds of intending to use a booster dose than completely agreeing that they were harmful (P < 0.001). Also, participants having no confidence at all in locally manufactured vaccines had 86% lower odds of intending to get a booster dose whereas participants with no confidence at all or no confidence in foreign manufactured vaccines had 97 to 88% lower odds of intending to take a booster dose than participants with complete confidence in locally and foreign manufactured vaccines respectively (P < 0.001). Participants with more than 25% of persons in their circle who were COVID-19 vaccinated had 118% to 205% higher odds of intending to take a booster dose than participants with 0–25% persons in their circle who were vaccinated (P < 0.05).

Table 2: Factors associated with intention to use a COVID-19 vaccine booster dose among vaccinated participants from Egypt (n = 1064) in multiple binary logistic regression (logit model) and estimated marginal effects.
Full size table

In multiple regression, intending to take a booster dose was significantly associated with not agreeing (P < 0.001) or not agreeing at all (P = 0.001) that vaccines were harmful. Those who did not agree that vaccines were harmful had 387% higher odds and those who did not agree at all that vaccines were harmful had 746% higher odds of intending to take a booster dose than those who completely agreed that vaccines were harmful. There was a significant association between intending to take a booster dose and having no confidence or no confidence at all (P < 0.001) in foreign manufactured vaccines. Those with no confidence had 79% lower odds and those with no confidence at all had 86% lower odds of taking a booster dose than those with complete confidence in foreign manufactured vaccines.

Based on the regression estimates in the logit model, the logit equation was.

log(p/1-p) = -0.668 + 0.017*χ1 – 0.115*χ2 – 0.505*χ3 + 0.666*χ4-1 +  + 0.623*χ4-2 + 0.184*χ4-3 + 0.0.815*χ4-4 + 0.166*χ5 + 0.194*χ6 + 0.433*χ7-1 – 0.622*χ7-2 + 0.267*χ7-3 + 0.220*χ7-4 – 0.032*χ8 – 0.222*χ9-1 – 0.013*χ9-2 + 0.066*χ10-1 + 0.164*χ10-2 + 2.105*χ11-1 + 1.622*χ11-2 + 0.852*χ11-3 + 0.046*χ11-4 – 0.361*χ12-1 + 0.604*χ12-2 + 1.093*χ12-3 – 2.207*χ13-1 – 1.697*χ13-2 – 0.431*χ13-3 – 0.547*χ14-1 + 0.105*χ14-2 – 0.212*χ14-3 + 0.011*χ15.

where p is the probability of intending to take a booster dose of the COVID-19 vaccine, χ1 to χ15 are the variables listed in Table 1 and χ4-1 to χ4-4,….. are the categories of the variable χ4 and so on.

The estimated marginal effects in Table 2 show the same directions of relationships as the UORs and the AORs. In unadjusted analysis, the greatest differences between subgroups in intention to use a booster dose marginal effects were between participants who agreed that vaccines were not at all harmful and those who completely agreed they were harmful (90.1 and 22.9%) which were reduced in adjusted analysis to 76.9 and 28.8% respectively and the difference between participants who had no confidence at all in foreign manufactured vaccines and those who had complete confidence in them (20.5 and 89.4%) which were reduced in adjusted analysis to 24.9 and 75.1% respectively

Discussion

The study showed that in a group of vaccinated, university-educated students living in Egypt, intention to take a COVID-19 vaccine booster dose differed based on the attitude toward COVID-19 vaccine harm and confidence in foreign manufactured vaccines. An attitude considering the vaccine safe was associated with higher odds of intention to take a booster. Participants with no confidence in foreign manufactured vaccines had lower odds of intending to take a booster dose. Attitude toward COVID-19 vaccines seemed to have the greatest impact on intention to take a COVID-19 booster dose whereas perceived control, social norms and perceived susceptibility may have less importance. The study suggests that educational programs promoting COVID-19 vaccination should focus on changing the attitude of educated persons toward COVID-19 vaccines. The findings partly support the study hypothesis.

The present study has some limitations. The study is limited by its cross-sectional design which does not prove causality and can only show associations. Online surveys, like the one used in the present study and in most COVID-19 studies, are likely to have some selection bias because it is not possible to use random samples when the survey is posted online. The convenience sampling, which was used instead, meant that some subgroups had a higher probability of being included in the sample than others. In the present study, the sample mostly consisted of university students whereas statistics show that about 30% of Egyptians are illiterate40. Thus, the sample was skewed to university-educated persons. Also, the questionnaire was distributed through an online platform whereas the internet penetration rate in Egypt was 71.9% in 202241. Thus, specific groups in the population were under-represented because they had less access to the Internet. Therefore, although most regions in Egypt were represented, the findings may not apply to the general Egyptian population. We assessed participants’ income level, but most participants were university students who were still dependent on their parents for financial support. They reported the allowance they received from their parents as income and this would underestimate their socio-economic level. It is important to consider the sample profile when generalizing the study findings. The results are applicable to young, university-educated students with similar cultural backgrounds. Older populations with less education may have a lower level of intention to receive booster doses of the COVID-19 vaccine. Nevertheless, the study has several strengths including the large sample size, the wide geographic coverage at national level and the use of behavioural change theories to explain the health behaviour.

The study had several important findings. First, about three quarters of the participants, who were mainly university students, reported an intention to take a COVID-19 vaccine booster dose similar to a previous study12. Despite this, the percentage of people receiving the COVID-19 vaccine and its booster doses in Egypt remains one of the lowest worldwide21,25. It is important to address the obstacles preventing the intention to take the COVID-19 vaccine and its booster dose from becoming actual behaviors and to monitor the reduction in this gap as time passes and misinformation about the COVID-19 vaccines dispel. It is also important to acknowledge the importance of vaccine hesitancy beyond the COVID-19 pandemic context and how it impacts the spread of vaccine-preventable diseases worldwide42 which adds to the importance of the present study.

Second, people with a history of COVID-19 infection had 30% higher odds of expressing an intention to take a booster dose in unadjusted analysis. The physical and mental impact of COVID-19 infection43 may increase perceived vulnerability causing affected individuals to seek the protection offered by COVID-19 vaccine booster doses44. Our findings disagree with research45 showing that previous COVID-19 infection was associated with disinclination to receive boosters. The difference between this and our study may be attributed to the time of data collection. Earlier research might have been conducted at a stage in the pandemic when people believed that COVID-19 infection conferred lifelong immunity with no need for vaccination among those who have already been infected46.

Third, the awareness that vaccination was mandatory seemed not to be related to perceived control of the uptake of booster doses in the present study and was not significantly associated with the intention to take a booster dose. Vaccination mandates have faced opposition, with citizens demonstrating against them in several countries47. Research48 showed that mandates were likely to increase vaccination in countries where vaccination rates were initially modest, if vaccine supplies were available, in subgroups likely to face penalties if they did not follow the mandates such as visitors not allowed inside public facilities without proof of vaccination. These conditions applied to the participants in the present study. However, the question we used in the survey was about mandated COVID-19 vaccination not its booster dose which was not specifically mandated in Egypt.

Fourth, perceiving that more persons were vaccinated in one’s circle was associated with 118% to 205% higher odds of intention to take a booster dose in unadjusted analysis. In our study, 76% of participants thought that at least half the people in their circles were vaccinated. This perception of high vaccination rate may be because of the governmental decree preventing non vaccinated persons from entering public facilities in Egypt49. Campaigns in universities resulted in higher vaccination rates than the general population50. It is important to note that the intention to take a booster dose was not associated with being a student or with awareness that vaccination was mandated but was associated with perceiving vaccination to be the norm. This emphasizes the importance of perceived norms in shaping one’s intentions compared to rules or group membership per se. However, the observed association was not significant in the adjusted analysis when attitude was included. The complex interplay between the individual and the community, attitude and norms, intention and actual behavior needs exploration in future studies.

Fifth, a positive attitude toward the COVID-19 vaccine harmlessness was associated with 387% to 746% significantly higher odds of intention to take a booster dose in agreement with previous studies in other countries51,52 and in Egypt53. There was also greater confidence in foreign than locally manufactured vaccines, which disagrees with research showing bias to locally produced vaccines54. This difference may be because at the time of the study, Egypt had just started to locally manufacture the Sinovac vaccine23, and not all participants were aware of this development. Another reason may be related to the low confidence in the Sinovac vaccine itself55. However, the WHO selected Egypt and five other countries in Africa to produce the Pfizer-BioNTech® and the Moderna® vaccines56. Confidence in these vaccines may differ from that in the Sinovac vaccine and this needs to be assessed in future studies.

Sixth, in this study, attitude was significantly associated with intention to take a COVID-19 vaccine booster dose in adjusted regression where participants with no confidence in foreign manufactured vaccines had 79–86% lower odds of intending to take a booster dose. This finding agrees with studies from Germany57 and China58 showing that attitude toward the vaccine was associated with vaccination intention. By contrast, studies from Ethiopia59, India60, Pakistan61, and the United States62 reported associations between attitude, norms and control with vaccination intention. Other studies63,64,65,66 showed that both the TPB and the HBM constructs were associated with vaccination indicating the complexity of booster uptake as a behavior and possible specificity of country-level determinants.

Conclusion

This study showed that most young and university-educated Egyptians participating in the study intended to take a COVID-19 vaccine booster dose and that this intention was associated with attitude toward vaccine harm and confidence in foreign vaccines. Even among young and university-educated individuals, unfavorable attitudes may negatively impact full vaccination and, therefore, the control of pandemics. Awareness campaigns are needed to overcome the negative attitudes and disinformation that discourage people from taking booster doses.