Table 1.

Main characteristics of the studies included in the review (n/r = not reported or not explicitly reported).

Author, year	Setting	Period of study	Method	Inclusion criteria	Participants	Investigated vaccine	Sociodemographic characteristics	Attitude toward vaccination
Olagoke, 2020	USA	22 March 2020	Survey	->18 years old -Living in USA	501	COVID-19	-Mean age 32.44 (SD 11.94) years -Females 55.29% -White 53.71% -Employed 53.71%	-Black/African, unemployed, and with personal belief against vaccines had lower COVID-19 vaccination intention -Religiosity was negatively correlated with COVID-19 vaccination
Kreps, 2020	USA	9 July 2020	Questionnaire	-US adults	1971	2 Hypothetical COVID-19 vaccinesa	-Median age 43 years (range 30–58) -Females 51% -White 73%	-56% participants declared to choose the presented vaccine -A greater vaccine efficacy, a longer protection duration and a lower incidence of side effects were associated to a higher probability of choosing a vaccine -Respondents were less likely to choose vaccines developed outside of the United States, particularly from China -Respondents who declared Democratic political partisanship were significantly more likely to choose to receive vaccination -Women, black, low education, and low age were associated to a lower willingness to receive vaccination
Salali, 2020	UK and Turkey	May 2020	Survey	->18 years old -Living in UK or Turkey	-1088 in UK -3936 in Turkey	COVID-19	n/r	-31% (Turkey) and 14% (UK) were unsure to be vaccinated -3% in both countries refused to be vaccinated -Acceptance was higher among those who believed the natural origin of pandemics, among those who had higher anxiety related to COVID-19 -Men were more likely to accept vaccines -Have a graduate degree and children decreased the odds of vaccine acceptance in Turkey, but not in UK
Ward, 2020	France	April 2020	Cross-sectional online survey	n/r	5018	COVID-19	-<35 years old (N = 1290) -35–64 years old (N = 2494) ->64 years old (N = 1234) -Females (N02629) -Males (N = 2389)	-Women, young people (<35 years old) and those with a lower income were more likely to refuse vaccines -No difference was observed between those who were diagnosed with COVID-19 and those who were not -Those who were highly concerned about being infected were less likely to refuse the vaccine -Those who felt close to radical parties or those who did not vote/did not feel close to any party were significantly more likely to refuse the vaccine -Most given reasons to refuse vaccine were: being against vaccines in general (27.6%), thinking that a vaccine produced in a rush is too dangerous (64.4%), considering the vaccine useless because of the harmless nature of COVID-19 (9.6%). Other respondents refused vaccine because of a general lack of trust, doubts about the efficiency of the vaccine or belief to be already immunized
Pogue, 2020	USA	n/r	Survey	n/r	316	COVID-19	-<18 years old 2.16% -18–25 years old 12.45% -26–35 years old 18.21% -36–45 years old 31.48% -46–55 years old 3.4% ->55 years old 32.41% -Females 49.38% -White 63.27%	-Respondents routinely vaccinated were more likely to receive COVID-19 vaccine -Respondents who had a greater perceived impact of COVID-19 in America were more likely to receive COVID-19 vaccine -Income and political ideology had no relationship with the attitude toward vaccination -68.57% of respondents indicated they were amenable to receive the vaccine -15.89% neither agreed or disagreed -The main reasons to refuse vaccine were: concerns about safety (45.45%) and lack of trust in the source (13.54%) and other reasons (15.45% – above all more testing before accepting vaccine)
Graffigna, 2020	Italy	Early days of the so-called phase 2	Survey	-Italian adult citizens	1004	COVID-19	-18–38 years old 34.4% -39–52 years old 33.6% ->52 years old 32.1% -Females 50.9%	-58.6% of respondents indicated they agreed to receive the vaccine -15.4% disagreed -26.2% were uncertain about receiving the vaccine -Respondents with a general positive attitude toward vaccine were more likely to receive COVID-19 vaccine -There was a positive relationship between health engagement and willingness to vaccinate
Detoc, 2020	France	26 March 2020–20 April 2020	Survey	n/r	3259	COVID-19	-<30 years old 20.6% -30–49 years old 46.11% -50–64 years old 24.6% -65–80 years old 8.3% ->80 years old 0.4% -Females 67.4% -24.1% had chronic medical conditions	-Vaccine hesitancy 35.3% -77.6% will certainly or probably be vaccinated against COVID-19 -83.1% men and 74.2% women were COVID-19 vaccine acceptors (P < 0.05) -81.5% healthcare workers and 73.7 non-healthcare workers were COVID-19 vaccine acceptors (P < 0.05) -Older age, male gender, fear about COVID-19, be healthcare workers and individual perceived risk were associated with COVID-19 vaccine acceptance
Fisher, 2020	USA	16–20 April 2020	Survey	-Adults	991	COVID-19	-18–29 years old 20.4% -30–44 years old 25% -45–59 years old 24.6% ->60 years old 30% -Females 51.5% -White 63.3%	-57.6% participants intended to be vaccinated -31.6% were not sure -10.8% did not intend to be vaccinated -Females, young, black/hispanic, those with a lower education and income, those who did not receive influenza vaccine were less likely to have intention to accept vaccination -The main reasons to refuse vaccine were: concerns about the vaccine, need additional information, anti-vaccine attitude, low trust in vaccine development
Palamenghi, 2020	Italy	Phase 1 (early days after initial spread of SARS-COV-2) and Phase 2 (early days after the Italian reopening after lockdown)	Survey	-Italian citizens	968 (phase 1) 1004 (phase 2)	COVID-19	n/r	-59% of participants intended to be vaccinated (Phase 2) -Decrease in trust toward scientific research, and vaccines' efficacy -Middle age group had a reduced willingness to be vaccinated compared with 18–34 years old people and over 60 years old people.
Dror, 2020	Israel	March 2020	Survey	-Healthcare personnel or general population	1941	COVID-19	n/r	-No difference in vaccine acceptance among healthcare personnel or not -Males, those who perceived themselves at higher risk of infection, people currently vaccinated against influenza had a higher acceptance -The rate of acceptance of COVID-19 vaccine was lower than the acceptance of Influenza vaccine among healthcare workers
Barello, 2020	Italy	n/r	Cross-sectional study	-Students	934	COVID-19	-Mean age 23.6 (SD 4.9) years old -Females 79.6%	-86.1% chose to be vaccinated -13.9% refused to be vaccinated -No significant differences were observed for socio-demographic characteristics or for type of study (healthcare students or not)
COCONEL Group, 2020	France	27–29 March 2020	Online survey	-French population over 18 years old	1012	COVID-19	n/r	-26% refused to be vaccinated -Refusals were higher among low-income people, young women and older than 75 years old -Those who voted for far left or far right candidate in the last elections were more likely to refuse vaccination
Grech, 2020	Malta	11–16 September 2020	Questionnaire	-Healthcare workers	1002	COVID-19 and influenza	n/r	Influenza: -Significant increase in willingness to be vaccinated (from 49% to 69%) COVID-19 -Almost 50% expressed their willingness to be vaccinated -Almost 25% were undecided and almost 25% did not want to be vaccinated -Men were more likely to accept vaccine
Wang, 2020	Hong Kong	26 February – 31 March 2020	Survey	-Nurses (not retired or working in administrative or academic positions)	806	COVID-19 and Influenza	-18–29 years old 22.7% -30–39 years old 36% -40–49 years old 24.2% ->50 years old 17.1% -Females 80.8% -25.8% had chronic medical conditions	Influenza: -Similar acceptance rate between 2019 and 2020 (47.5% and 44.7% respectively) COVID-19 -40% nurses had intention to accept COVID-19 vaccination -Males, those with chronic diseases, or those who accepted the seasonal influenza vaccine in 2019 were more likely to have intention to accept COVID-19 vaccination -The main reasons to refuse vaccine were: suspicion on efficacy, effectiveness, safety (76.43%); believing vaccination is not necessary (18.05%)
Goldman, 2020	USA, Canada, Israel, Japan, Spain, Switzerland	27 march 2020–30 June 2020	Survey	-Parents or caregivers of patients older than 1 year and younger than 19 years old	2422	Influenza	-274 (26.7%) +102 (24.4%) fathersb -723 (70.5%)+299 (71.5%) mothersb -Mean age 40.7	-54.3% intended to vaccinate their children (+15.9% compared to the past 12 months) -58.3% intended to receive a vaccine for themselves -1025 had no intention to vaccinate their children -Parents who received vaccination or vaccinated their children in the past or those who were worried about COVID-19 had a higher probability to vaccinate their children

^aBecause the study was conducted before the development of a vaccine

^bCalculated respectively on who do not want plan to vaccinate (1025) and who plan to vaccinate (418)