The emergence and spread of SARS-CoV-2 has caused significant morbidity and mortality across the globe. As of August 2022, the number of total worldwide confirmed COVID-19 cases is estimated to be over 600 million, and over 6.5 million COVID-19-related deaths have been recorded [1]. Moreover, the COVID-19 pandemic continuous to threaten public health since breakthrough infections and new contagious variants of SARS-CoV-2 affect even fully vaccinated individuals ^[2][3][2,3].

The impact of the pandemic on healthcare workers (HCWs) has been unprecedented; between 80,000 and 180,000 HCWs died from COVID-19 between January 2020 and May 2021 according to WHO data [4]. HCWs are at increased risk of COVID-19 and hospitalization due to close and long contact with COVID-19 patients and occupational exposure to SARS-CoV-2 [5]. “Front-door” and patient-facing HCWs are at higher risk for COVID-19-related outcomes ^[6][7][6,7]. According to a meta-analysis with 119,883 HCWs, 51.7% of HCWs became infected with SARS-CoV-2 [8], while another meta-analysis with 230,398 HCWs found that 5% of COVID-19 cases in HCWs had severe complications, and 0.5% of HCWs died [9].

Globally, HCWs were among the first groups to be offered the COVID-19 vaccines since they are a high-risk group during the pandemic. Although safety and effectiveness of COVID-19 vaccines are proven both in randomized clinical trials ^[10][11][10,11] and real-world studies ^[12][13][12,13], COVID-19 vaccination hesitancy in HCWs worldwide continues to be a challenge ^[14][15][16][14,15,16]. For instance, the average prevalence of COVID-19 vaccination hesitancy worldwide in a total sample of 76,471 HCWs from 21 countries was 22.51%, ranging from 4.3 to 72% [14]. Sociodemographic factors (female gender, younger age, nurse profession, absence of history of influenza vaccination), concerns about vaccine safety and effectiveness, fear of adverse events, lack of information about vaccination, and mistrust of government and institutions are associated with COVID-19 vaccination hesitancy ^[14][17][18][14,17,18].

The overall prevalence of COVID-19 vaccine uptake among HCWs, 77.3%, is higher than that detected in the general population, 67.6% ^[19][57]. This finding is confirmed by the literature since HCWs are more likely than the general population to accept a COVID-19 vaccine ^[20][21][58,59]. Lack of scientific knowledge and low understanding of COVID-19 vaccines among non-healthcare workers could explain the higher acceptance rate of healthcare workers.

Although the study showed a high COVID-19 vaccine uptake rate among HCWs, not all of them received a COVID-19 vaccine. In particular, an important percentage (22.7%) of the HCWs in our study refused vaccination despite availability and accessibility showing that HCWs are not immune to vaccine hesitancy. Indeed, the WHO defines vaccine hesitancy as 1 of the 10 most important threats to global health in 2019 ^[22][60]. It is necessary to increase the uptake of COVID-19 vaccination by HCWs since they provide care to COVID-19 patients, and high infection rate among HCWs could result in a significant reduction in this essential workforce. Moreover, vaccinated and well-informed HCWs are an important source of COVID-19 vaccine information and are more likely to recommend COVID-19 vaccination to families, colleagues, and their patients ^[23][61]. HCWs should inform individuals and especially patients about the safety and effectiveness of COVID-19 vaccination since their vaccine hesitancy may exacerbate patient hesitancy ^[24][62]. HCWs are trusted professionals and could serve as a role model of healthy behavior of the general population, improving vaccine coverage ^[25][63].

The findings demonstrate the highest prevalence of COVID-19 vaccine uptake among HCWs in North America (85.6%) and the lowest prevalence among those in Africa (65.6%). A similar trend is observed in the vaccination of the general population worldwide since the percentage of population to have received at least one dose of a COVID-19 vaccine is 80% in North America and Asia, 69% in Europe, and 27% in Africa ^[19][57]. The majority of the countries in Africa missed the WHO targets: 40% of a country’s population should have been vaccinated by end December 2021, and 70% by mid-2022 ^[26][64]. Inconsistent supply of COVID-19 vaccines to Africa, low country-level preparedness against a pandemic, vaccine hesitancy, and distrust are the main reasons for the low vaccination uptake in Africa ^[26][64]. Africa’s low vaccination rate is a threat to global effectiveness of COVID-19 vaccines since new variants could emerge from populations with low vaccine coverage. Therefore, positive attitudes of HCWs in Africa towards COVID-19 vaccination is paramount since they are a professional trusted source of information, and their opinion could improve vaccination coverage ^[27][65].

2.2. Predictors of COVID-19 Vaccine Uptake

Variation in vaccine uptake across races since white HCWs are more likely to receive a COVID-19 vaccine. Several studies in the general population confirm that COVID-19 vaccination uptake is higher among white individuals than ethnic minority groups and especially black individuals ^[28][29][30][66,67,68]. Reduced vaccine uptake in ethnic minority groups is not unique to COVID-19 since this phenomenon was also observed for the H1N1 flu pandemic in 2009 ^[31][32][69,70]. Ethnicity is interrelated with other barriers to COVID-19 vaccine uptake, such as lower educational level and socioeconomic status, religion, belief in conspiracy theories, and lack of trust in the government, healthcare systems, and employers ^[33][34][35][71,72,73]. These findings give significant cause for concern, since SARS-CoV-2 infection rate and COVID-19-related adverse outcomes are higher in these groups ^{[6][36][37][38]}[6,74,75,76]. Thus, there is an urgent to implement targeted interventions in order to overcome barriers to COVID-19 vaccination in ethnic minority groups ^[34][35][39][72,73,77]. Physicians were more likely to be vaccinated than other staff groups. Moreover, the overall prevalence of COVID-19 vaccine uptake among physicians in our meta-analysis, 83.6%, is higher than that detected for nurses, 77.4%. Concerns about the safety, effectiveness, and side effects of COVID-19 vaccines and lack of perceived need for vaccination are the main reasons for vaccine hesitancy among nurses ^[40][41][78,79]. Nurses’ unwillingness to accept a COVID-19 vaccine is concerning since they are among the most trusted HCWs, and their attitudes towards vaccination can influence patient vaccination decisions ^[42][43][80,81]. Moreover, nurses are the frontline HCWs that provide direct care to COVID-19 patients, and thus nurses’ occupational risk of exposure to SARS-CoV-2 is very high ^{[44][45][46][47]}[82,83,84,85]. The situation is worse for the nurses in ethnic minority groups since they have already been disproportionately affected by the pandemic. For instance, Filipino nurses comprise 25% of COVID-19-related deaths among nurses in the USA, although they make up 4% of the nursing workforce in the country ^[48][86]. Confidence in COVID-19 vaccine safety and effectiveness was found to be a positive predictor of COVID-19 vaccine uptake in our systematic review. Negative attitudes towards COVID-19 vaccination, concerns for side effects and future effects, and lack of confidence in safety and effectiveness are more common among unvaccinated HCWs ^[49][50][51][44,87,88]. The novelty and the rapid production of COVID-19 vaccines worldwide could explain mistrust of HCWs ^[52][89]. It is reasonable that some HCWs may have delayed vaccination until new data emerged. Therefore, additional and updated information about safety and effectiveness of vaccines may increase vaccine acceptance among HCWs. Detailed data on safety and surveillance regarding the COVID-19 vaccines could help HCWs to overcome their fear and hesitancy. Seasonal influenza vaccination is a positive predictor of COVID-19 vaccine uptake. Flu vaccination denotes a positive attitude of HCWs towards vaccines, and promotion of annual influenza vaccination may have a positive effect in future COVID-19 vaccine acceptance. A psystemapertic review has already shown that influenza vaccination positively affects HWCs’ intention to receive a COVID-19 vaccine ^[53][21]. However, since the flu vaccination rate among HCWs is low ^[54][55][90,91], investment and promotion of seasonal influenza vaccination is crucial. Direct care for COVID-19 patients was associated with vaccine uptake among HCWs. The literature supports this finding since a scoping review of 35 studies with 16,158 HCWs that found that HCWs that provide care to COVID-19 patients are more likely to accept COVID-19 vaccines [14]. Direct patient care may be associated with higher severity perception of COVID-19, which drives nurses to be vaccinated more often [56]. It is not surprising that older age was a positive predictor of COVID-19 vaccine uptake among HCWs. Early studies in the general population of the USA confirm this finding since vaccination coverage is lower and increased more slowly over time among younger adults ^[29][57][67,92]. Older age is a well-known significant predictor of COVID-19 mortality ^[58][59][93,94]. Thus, older adults may feel more vulnerable to COVID-19, which probably encourages them to take a COVID-19 vaccine considering health benefits. On the other hand, younger adults may perceive a lower personal risk of COVID-19-related outcomes. There is a prior SARS-CoV-2 infection is associated with a decrease in COVID-19 vaccine uptake. This finding can be explained by the fact that HCWs with a confirmed SARS-CoV-2 infection may believe that they have acquired sufficient immunological protection ^[60][41]. However, waning humoral immunity to SARS-CoV-2 in those who have had confirmed COVID-19 ^[61][95] and new variants of SARS-CoV-2 [2] threaten people’s immunization and increase risk of infection over time.

3. Conclusions

It found that 77.3% out of 555,561 HCWs worldwide have received at least one dose of a COVID-19 vaccine. The overall prevalence of COVID-19 vaccine uptake was 83.6% and 77.4% for physicians and nurses, respectively. Being older, white, or a physician; receiving the seasonal influenza vaccine; providing care to COVID-19 patients; and trusting COVID-19 vaccines were enabling factors for the COVID-19 vaccine uptake. Deep understanding of the factors that influence HCWs’ decisions to receive a COVID-19 vaccine is critical to implementing tailored communication strategies for HCWs who are at risk for not getting vaccinated, e.g., HCWs who belong to ethnic minority groups.