Table 1.

Characteristics of the included studies

Study author, year	Country	Study type	Median age	Age range	Male(%,case/control)	Severe/immune	Severe/naive	Mild/immune	Mild/naive	NOS/Jadad
Adrielle Dos Santos Letícia et al. (2021)[23]	Brazil	Observational study	39.2	18–58	21.2/37.1	12	35	21	27	5
Hall et al. (2021)[12]	England	Observational study	45.7	18–85	17.2/14.9	50	1126	105	578	6
Murillo-Zamora et al. (2021)[13]	Mexico	Observational study	NA	≥ 20	NA	38	48,057	220	84,131	5
Bailly et al. (2021)[14]	France	Observational study	87.0	≥ 77	NA	2	4	11	1	5
Singh et al. (2021)[15]	India	Observational study	55.0	50–63	35.6/64.4	89	211	98	179	8
Slezak et al. (2021)[16]	America	Observational study	NA	≥ 15	NA	29	4094	286	71,055	6
Baden et al. (2020)[17]	America	RCT	51.4	≥ 18	52.2/53.1	4	43	7	142	6
Logunov et al. (2021)[18]	Russia	RCT	NA	≥ 18	61.1/61.5	0	20	16	42	8
Polack et al. (2020)[19]	Multinational	RCT	52	16–91	51.1/50.1	1	9	7	153	7
Sadoff et al. (2021)[20]	Multinational	RCT	52	≥ 18	55.1/54.7	14	60	103	291	7
Madhi et al. (2021)[21]	South Africa	RCT	NA	18–65	NA	4	6	15	17	6

NA Not available, NOS Newcastle–Ottawa scale, Jadad Modified Jadad scale

Severe/immune: Cases diagnosed as severe after natural infection/vaccination

Severe/naive: Cases diagnosed as severe in the initial infection

Mild/immune: Cases diagnosed as mild after natural infection/vaccination

Mild/naive: Cases diagnosed as mild in the initial infection