Figure 1. Flowchart of inclusion of studies.

Figure 2. Forest plots with point estimates and 95% confidence intervals of effectiveness of COVID-19 vaccines against (A) infection, (B) symptomatic illness, (C) hospitalization, and (D) death. N denotes total number of participants per study, as numbers per group were usually not available [20,22,23,25,26,27,29,31,32,33,34,35]. Figure 3. Forest plots with point estimates and 95% confidence intervals of odds ratios for A. infection with COVID-19, or B. severe COVID-19 for vaccinated persons with diabetes, compared to vaccinated persons without diabetes. N denotes total number of participants per study, as numbers per group were usually not available. Ad5, Ad5-nCoV-S (CanSino); AZD, AZD-1222 (AstraZeneca); BNT, BNT162b2 (Pfizer); JNJ, JNJ-78436735 (Janssen); mRNA, mRNA-1273 (Moderna) [19,21,24,28,30].

Table 1. Characteristics of included studies.

Table 1. Characteristics of included studies.

StudyCountryDesignPersons (N)Persons with DM
(N, %)Mean age, years eWomen (%) eVaccine Type(s)Vaccine doseCOVID-19
Outcomes
(in persons with DM)Comparison: vaccinated patients with diabetes vs. unvaccinated patients without diabetesAlsaffar et al., 2022 [20]Saudi ArabiaRetrospective record review260104 (40)5246BNT162b2
AZD12221 or 2DeathChodick et al., 2022 [31]IsraelRetrospective cohort study872,454104,152 (12)5252BNT162b22Infection
Symptomatic illnessDagan et al., 2021 [32]IsraelMatched case-control study1,193,236131,541 (11)4550BNT162b21 or 2Infection
Symptomatic illnessDrawz et al., 2022 [22]USTest-negative study, and cohort study4,547,945322,090 (7) cNR aNRBNT162b2
mRNA-12732 dInfection
HospitalizationHitchings et al., 2021 [23]BrazilMatched case-control study61,36010,627
(17)6758AZD12221InfectionNiessen et al., 2022 [25]The Nether-landsTest-negative case-control study634155
(24)6843BNT162b2
AZD1222
mRNA-12731 or 2HospitalizationPilishvili et al., 2021 [26]USTest-negative case-control study4931228
(5)3783BNT162b2
mRNA-12731 or 2Symptomatic illnessRanzani et al., 2021 [33]BrazilMatched test-negative case-control study55,51911,847
(21)7656CoronaVac1 or 2Symptomatic illnessSaciuk et al., 2022 [27]IsraelRetrospective cohort study1,650,885136,777
(8)NR a52BNT162b22InfectionTenforde et al., 2021 [34]USProspective observational case-control study1212388
(32)NR a49BNT162b2
mRNA-12731 or 2HospitalizationWhitaker et al., 2022 [35]England, UKCohort study, and test negative case-control study5,591,142407,741 (7)NR aNRBNT162b2
AZD12221 or 2Symptomatic illness
Hospitalization DeathYoung-Xu, 2021 [29]USMatched test-negative case-control study75,54625,429
(34)NR a10BNT162b2
mRNA-12731 or 2InfectionComparison: vaccinated patients with DM vs. vaccinated patients without DMAgrawal et al., 2021 [19]Scotland, UKProspective cohort study2,527,008264,243 (10)NR a55BNT162b2
AZD12221Severe diseaseBasso et al., 2022 [21]ItalyRetrospective cohort study142038 (3) c47 cNRBNT162b2
mRNA-1273
JNJ-784367352 bBreakthrough-
infectionMurillo-Zamora et al., 2022 [24]MexicoRetrospective cohort study1607NR5057JNJ-78436735
BNT162b2
Ad5-nCoV-S
CoronaVac1 or 2 bPneumoniaYek et al., 2022 [28]USProspective cohort study2246633 (28)NR a58BNT162b2
AZD1222
mRNA-12732 dSevere diseaseZaqout et al., 2021 [30]QatarRetrospective cohort study199,21939,994 (20)4242BNT162b21 or 2Infection