Table 3.
Certainty of the evidence.
| Outcome | Effect | Number of participants (studies) | Certainty of the evidence (GRADEa) | Comment |
| Uptake of vaccines assessed with Facebook, Healthy.me, WhatsApp, a website with vaccine interactive social media components, and Twitter (follow-up: mean 9 months) | Three studies showed a positive effect on the outcome [65,67,71]; 3 other studies did not show any effect [69,73,75] | 24,799 (6 randomized controlled trials) |
 (very lowb,c,d) |
We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. |
| Vaccine acceptance was assessed with Facebook, a website with vaccine information and social media components, YouTube, and Twitter (follow-up: mean 9 months) | The studies showed a positive effect on the outcome [63,68,70,72,74] | 2565 (5 randomized controlled trials) |
(very lowe,f,g) |
We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect. |
| Days unvaccinated assessed with a website with vaccine information and social media components (follow-up: 36 months) | The study showed a positive effect on the outcome [64] | 1093 (1 randomized controlled trial) |
 (highh,i,j) |
We are very confident that the true effect lies close to that of the estimate of the effect. |
aGRADE: Grading of Recommendations Assessment, Development, and Evaluation.
bTwo [73,75] of 6 studies were rated low quality, 2 studies [67,71] were rated fair quality, and 2 [65,69] were rated good quality in the risk-of-bias assessment. Two studies [67,71] were rated as having an unclear risk of bias due to insufficient information on the domain Selective reporting. Two studies [73,75] were rated as having an unclear risk of bias in 4 domains (Random sequence generation, Selective reporting, Other bias, and Incomplete outcome data).
cThe effect direction plot shows that 3 [65,67,71] of 6 studies reported a positive impact on the outcome (uptake of vaccines). Three of the studies [69,73,75] reported that the intervention had no effect on the outcome. The measures used in each study vary, so this made comparison of the studies difficult.
dThe total number of participants in these 6 studies was 24,799. Four studies [65,67,69,73] reported CI, and all of them, except from 1 [73], reported wide intervals. Three of the CIs [65,67,73] were significant (P=.02 and P=.03 [73], P=.008 [67], and P=.01 [65]).
eOne of 5 studies [74] was rated as having low quality in the risk-of-bias assessment. One study was rated as having fair quality [72], and 3 were rated as having good quality [63,68,70]. Two studies [70,72] were rated as having an unclear risk of bias in the domain Selective reporting, which is due to insufficient information to make a judgment.
fThe effect direction plot shows that all 5 studies included [63,68,70,72,74] reported a positive impact on the outcome (vaccine acceptance). The measures used in each study vary, so this makes it difficult to compare the studies.
gThe total number of participants was 2565. One study had n<60 [72]. Two studies reported CI. One was narrow and significant [63] and the other was wide and not significant [68].
hThis study [64] was rated as good quality in the risk-of-bias assessment.
iThe web-based vaccine information had a positive effect on parental vaccine behaviors.
jThis study had 1093 participants. The CI reported between the active group and the control group was significant.