Table 1.

The search strategy of the study

Database	Search string	Number of retrieved papers	Limits
Scopus	(TITLE-ABS-KEY (“covid19” OR corona OR “covid-19” OR “SARS-CoV-2”)) AND (TITLE-ABS-KEY (vaccine OR vaccination OR immunization OR immunisation)) AND (TITLE-ABS KEY (inequality OR inequity OR disparity OR distribution)) AND (LIMIT-TO (PUBYEAR, 2021) OR LIMIT-TO (PUBYEAR, 2020)) AND (LIMIT-TO (DOCTYPE, “ar”) OR LIMIT-TO (DOCTYPE, “re”)) AND (LIMIT-TO (LANGUAGE, “English”)) AND (LIMIT-TO (SRCTYPE, “j”))	2389	Language (only resources with at least an abstract in English), search the key words in title and abstract. Date: December 2020 (the first vaccination), up to 30 May, 2022
PubMed	Search: ((“covid19”[Title/Abstract] OR corona*[Title/Abstract] OR “covid-19”[Title/Abstract] OR “SARS-CoV-2”[Title/Abstract]) AND (vaccin*[Title/Abstract] OR immunization [Title/Abstract] OR immunization [Title/Abstract])) AND (inequality [Title/Abstract] OR inequity [Title/Abstract] OR disparity [Title/Abstract] OR distribution [Title/Abstract]) Filters: English, from 2020 to 2022	1125
WOS	TI = ((“covid19” OR corona OR “covid-19” OR “SARS-CoV-2”) AND (vaccine OR immunization OR immunisation OR vaccination) AND (inequality OR inequity OR disparity OR distribution)) AB = ((“covid19” OR corona OR “covid-19” OR “SARS-CoV-2”) AND (vaccine OR immunization OR immunisation OR vaccination) AND (inequality OR inequity OR disparity OR distribution))	916
ProQuest	TiAb(“covid19” OR corona OR “covid-19” OR “SARS-CoV-2”) AND ab (vaccine OR immunization OR immunisation OR vaccination) AND ab (inequality OR inequity OR disparity OR distribution)	193