Table 1.

Key words used in the search strategy.

Theme #	Theme	Key words (in title/abstract)
1	Reasons	Reasons OR reason OR motive OR motives OR motivation OR motivations
2	Child	Child OR children OR infant OR infants OR parents OR parents OR newborn OR newborns OR baby OR babies
3	Adolescent	Adolescents OR adolescent OR “young adult” OR “young adults” OR teenager OR teenagers OR teen OR teens
4	Vaccination	Vaccin* OR immunis* OR immuniz*
5	Under-vaccination	Complet* OR incomplete OR partial OR adherence OR adhesion OR compliance OR undervaccination OR under-vaccination OR under immunization OR underimmunization OR under-immunisation OR under-immunization OR coverage OR status OR dropout OR drop-out OR contin* OR suboptimal
6	Untimely vaccination	Delay* OR time*
7	Non-vaccination	Non-vaccin* OR non-immuniz* OR non-immunis* OR nonimmunis* OR nonimmuniz* OR nonvaccin*
8	Sub-Saharan Africa	Africa OR angola OR benin OR botswana OR “burkina faso” OR burundi OR cameroon OR “cape verde” OR “central african republic” OR chad OR comoros OR “democratic republic of the congo” OR “republic of the congo” OR djibouti OR equatorial guinea OR “guinea-bissau” OR guinea OR eritrea OR ethiopia OR gabon OR gambia OR ghana OR ivory coast OR “cote d’ivoire” OR kenya OR lesotho OR liberia OR madagascar OR malawi OR mali OR mauritania OR mauritius OR mozambique OR namibia OR niger OR nigeria OR rwanda OR “sao tome and principe” OR senegal OR seychelles OR “sierra leone” OR somalia OR “south africa” OR swaziland OR eswatini OR sudan OR south sudan OR tanzania OR togo OR uganda OR zambia OR zimbabwe

Notes: Search 1 AND (2 OR 3) AND 4 AND (5 OR 6 OR 7) AND 8.