Characteristics of eligible studies
| Nudging approach | Authors (year, journal) | Study location | Study population | Sample size | Study design | Target disease | Outcome measures* |
| Make available information salient | Lwembe et al (2016, BMC Family Practice)46 | UK | Parents or caregivers of children under 5, policymakers and practitioners | 31 parents,15 policymakers and 9 practitioners | Qualitative design: FGD, telephone interviews | Not specific (vaccine-preventable childhood diseases) | Perception of the intervention (+) |
| Borg et al (2018, Vaccine)47 | Australia | Parents or guardians of children (6 months–<5 years) | 5534 | RCT | Influenza | Vaccination uptake (influenza vaccine) (0) | |
| Uddin et al (2016, Vaccine)53 | Bangladesh | Pregnant women, mothers with children aged 0–11 months, and Expanded Program on Immunisation (EPI) service providers in study areas | 4158 | Non-randomised (quasi-experimental) | Not specific (vaccine-preventable childhood diseases) | Vaccination uptake (all childhood vaccines) (+) | |
| Ahlers-Schmidt et al (2012, Vaccine)54 | USA | Parents of newborns | 90 | RCT (pilot study) | Not specific (vaccine-preventable childhood diseases) | Vaccination uptake (all childhood vaccines) (−) | |
| Kim et al (2018, JAMA Network Open)56 | USA | Adult patients | 96 291 | Quantitative descriptive study (Quality improvement) | Influenza | Vaccination uptake (influenza vaccine) (+) | |
| Patel et al (2017, Journal of General Internal Medicine)55 | USA | Adults | 45 926 | Non-randomised (observational study) | Influenza | Vaccination uptake (influenza vaccine) (+) | |
| Changolkar et al (2020, PLoS One)57 | USA | Primary care physicians from 10 primary care practices | 56 | Non-randomised study (quasi- experimental) | Influenza | Vaccination uptake (influenza vaccine) (+) | |
| Duvall (2019, Pediatric Nursing)58 | USA | Families of paediatric inpatients older than 6 months of age, physicians and nurses | 173 | Quantitative descriptive study (quality improvement) | Influenza | Vaccination uptake (influenza vaccine) and perception of intervention (+) | |
| Milkman et al (2011, Proceedings of the National Academy of Sciences of the USA (PNAS))59 | USA | Employees aged >50 years | 3272 | RCT | Influenza | Vaccination uptake (influenza vaccine) (+) | |
| Kempe et al (2013, American Journal of Public Health)60 | USA | Parents of children who were aged 19–35 months | 31 567 | RCT | Not specific (vaccine-preventable childhood diseases) | Childhood immunisation status (up to date) and cost-comparison benefit (+) | |
| Szilagyi et al (2020, JAMA Internal Medicine)61 | USA | Patients in 52 primary care practices | 164 205 | RCT | Influenza | Vaccination uptake (influenza vaccine) (+) | |
| Porter et al (2018, Vaccine)63 | USA | Parents with daughters aged 9–17 years | 761 | RCT | HPV | Intention to vaccinate and vaccine confidence (−) | |
| Saitoh et al (2017, Human Vaccines and Immunotherapeutics)62 | Japan | Pregnant women | 160 | RCT | Influenza and PCV13 | Parental attitudes and beliefs towards vaccines and their infant’s vaccination uptake (0) | |
| Joseph et al (2016, Clinical Pediatrics)64 | USA | Mothers with daughters aged 11–15 years | 200 | RCT (pilot study) | HPV | Vaccination uptake (HPV vaccine) and knowledge about vaccines (−) | |
| Staras et al (2021, BMC Public Health)48 | USA | Parents of adolescents aged 11–12 years | 286 | RCT (feasibility trial) | HPV | Feasibility and acceptability of vaccine reminders (+) | |
| Lorini et al (2020; Vaccines)50 | Italy | Nursing home workers | 1998 | Mixed-methods study | Influenza | Intention to vaccinate (influenza vaccine) (+) | |
| Schmidtke et al (2020, BMJ Quality and Safety)52 | UK | Healthcare workers | 7540 | RCT | Influenza | Vaccination uptake (influenza vaccine) (−) | |
| Chen et al (2020; Behavioural Public Policy)51 | USA | Adults aged 65–70 years | 208 867 | RCT | Influenza, tetanus, shingles and pneumonia | Vaccination uptake (influenza, shingles, tetanus, pneumonia vaccine) (+) | |
| Milkman et al (2021, PNAS)49 | USA | Patients in 2 large health facilities | 47 306 | RCT | Influenza | Vaccination uptake (influenza vaccine) (+) | |
| Maltz and Sarid (2020, Medical Decision Making)66 | Israel | Adults aged 18–65 years | 3271 | RCT | Influenza | Intention to vaccinate (influenza vaccine) (+) | |
| Panozzo et al (2020, Journal of Adolescent Health)65 | USA | Mothers with children aged 11–14 years | 762 | RCT | HPV | Intention to vaccinate (HPV vaccine) (−) | |
| Change the way outcomes are framed | Lechuga et al (2011, Annals of Behavioural Medicine)77 | USA | Mothers with daughters aged 9–17 years | 150 | Mixed-methods design (formative and experimental study) | HPV | Intention to vaccinate (HPV vaccine) (+) |
| Fahy and Desmond (2010, Irish Journal of Medical Science)76 | Ireland | Mothers with daughters aged 8–16 years | 72 | Non-randomised study (single group pre-test and post-test) | HPV | Attitudes towards vaccine and intention to vaccinate (HPV vaccine) (0) | |
| Liu et al (2019, Patient Education and Counselling)79 | China | Women aged 18–45 years | 453 | Quantitative descriptive study (Survey) | HPV | Intention to vaccinate (HPV vaccine) (0) | |
| Frew et al (2014, Vaccine)81 | USA | Pregnant women | 272 | RCT | Influenza | Intention to vaccinate (influenza vaccine) (−) | |
| Hendrix et al (2014, Pediatrics)82 | USA | Parents with an infant <12 months of age | 802 | RCT | MMR | Intention to vaccinate (MMR vaccine) (+) | |
| Motta et al (2021, Frontiers in Political Science)44† | USA | Adults | 7064 | RCT | COVID-19 | Intention to vaccinate (COVID-19 vaccine) (+) | |
| Freeman et al (2021, The Lancet Public Health)78 | UK | Adults (vaccine hesitant) | 18 855 | RCT | COVID-19 | Intention to vaccinate (COVID-19 vaccine) (+) | |
| Xu et al (2020, Aslib Journal of Information Management)80 | China | College students | 300 | Non-randomised study (quasi-experimental) | HPV | Intention and information need to vaccinate (HPV vaccine) (+) | |
| Okuno et al (2021, Pediatrics International)83 | Japan | Mothers | 81 | RCT | Haemophilus influenzae type b (HiB) and pneumonia (PCV) | Intention to vaccinate (HiB and PCV vaccines) (−) | |
| Invoke social norms | Lee et al (2018, Applied Nursing Research)84 | USA | Mothers and daughters aged 14–17 years | 18 dyads (mother and daughter) | Mixed-methods design (community-based participatory research with pilot RCT) | HPV | Intention to vaccinate and vaccination uptake (HPV vaccine) (0) |
| Attwell and Freeman (2015, Vaccine)85 | Australia | Parents with children | 304 | Mixed-methods design (evaluation study) | Not specific (vaccine-preventable childhood diseases) | Attitudes towards vaccine (−) | |
| Encourage emotional affect | Papapchrisanthou and Loman (2018; Public Health Nursing)86 | USA | Parents of infants aged 4–14 days | 40 | Non-randomised study | DTaP, Polio, Influenza, Hepatitis B and Pneumonia | Parental perception of immunisations, perceived knowledge of disease, comfort with immunisation decision making, satisfaction with provider and vaccine schedule adherence (0) |
| Blanchard et al (2020, Journal of Public Health)87 | USA | Adolescents aged 13–18 years | 598 | Non-randomised study (single group pre-test and post-test) | Not specific (vaccine-preventable childhood diseases) | Knowledge, attitudes and beliefs about vaccines (+) | |
| Kuru et al (2021, PLoS One)88 | USA | Adults | 2345 | RCT | MMR | Vaccine intentions (MMR vaccines) (+) | |
| Nyhan et al (2014, Pediatrics)91 | USA | Parents with children aged <17 years | 2229 | RCT | MMR | Perception about vaccine’s safety and intention to vaccinate (MMR vaccine) (−) | |
| Kepka et al (2011, Journal of Community Health)89 | USA | Parents with daughters aged 9–17 years | 88 | RCT | HPV | Vaccination awareness and uptake (HPV) (+) | |
| Cox et al (2010, Health Psychology)90 | USA | Mothers with daughters aged 11–16 years | 522 | RCT | HPV | Intention to vaccinate (HPV) (+) | |
| Change defaults | Giubilini et al (2019, HEC Forum)73 | UK | General population (61.9% are parents with children) | 457 | Quantitative descriptive study (survey) | MMR | Vaccination policy at schools (+) |
| Reiter et al (2012, Journal of Behavioural Medicine)74 | USA | Parents with adolescent sons aged 11–17 years | 404 | RCT | HPV, influenza and meningococcemia | Intentions to vaccinate (HPV, seasonal influenza and meningococcal vaccine) (0) | |
| Brewer et al (2017, Pediatrics)72 | USA | Primary care clinics with patients aged 11 or 12 years | 29 | RCT | HPV | Vaccination uptake (HPV vaccine) (+) | |
| Opel et al (2015, American Journal of Public Health)71 | USA | Paediatric providers and parents of children aged 1–19 months | 16 | Non-randomised (cross-sectional observational study) | Not specific (vaccine-preventable childhood diseases) | Parental verbal acceptance of recommended vaccines at visit’s end (0) | |
| Offer incentives | Zeng et al (2019, Vaccine)67 | China | Parents with young children aged 3–6 years | 1506 | Non-randomised (cross-sectional survey) | Influenza | Intention to vaccinate (influenza vaccine) (+) |
| Buttenheim et al (2016, Vaccine)45‡ | USA | Parents and caregivers of infants | 95 | RCT (feasibility study) | Tdap | Vaccination uptake (Tdap) (−) | |
| Bronchetti et al (2015, Journal of Economic Behaviour and Organisation)68 | USA | College students | 9358 | RCT | Influenza | Intention to vaccinate (influenza vaccine) (0) | |
| Rockliffe et al (2020, PLoS One)69 | UK | Students aged 13–14 years | 36 students (n=6 FGDs), 181 students | Qualitative design | HPV | Acceptability of financial incentives (0) | |
| Banerjee et al (2010, BMJ)70 | India | Households with children 0–5 years | 2188 | RCT | Not specific (vaccine-preventable childhood diseases) | Vaccination uptake (all childhood vaccines) (+) | |
| Change the messenger | Schoeppe et al (2017, Health Promotion Practice)75 | USA | Parent advocates | 33 (across three study years) | Mixed-methods design (evaluation study) | Not specific (vaccine-preventable childhood diseases) | Knowledge, attitudes and behaviour on vaccines (+) |
*The sign in the brackets indicates whether the results support the effectiveness of the respective intervention (+), indicate negative evidence for the effectiveness (−) or the results are mixed (0).
† Used an additional nudge - ‘Change the messenger’
‡ Used an additional nudge - ‘Invoke social norms’
DTaP, diptheria, tetanus and accelular pertussis; FGD, focus group discussion; MMR, measles, mumps and rubella; PCV13, pneumococcal conjugate; RCT, randomised controlled trial; Tdap, tetanus, diphtheria and pertussis.