| Level of evidence based on research design |
| I |
Evidence obtained from at least one properly randomized, controlled trial. |
| II-1 |
Evidence obtained from well-designed, controlled trials without randomization. |
| II-2 |
Evidence obtained from well-designed cohort or case-control analytic studies, preferably from more than one centre or research group (including immunogenicity studies). |
| II-3 |
Evidence obtained from comparisons between times or places with or without the intervention. Dramatic results in uncontrolled experiments could also be included in this category. |
| III |
Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees. |
| Quality (internal validity) rating |
| Good |
A study (including meta-analyses or systematic reviews) that meets all design-specific criteria* well. |
| Fair |
A study (including meta-analyses or systematic reviews) that does not meet (or it is not clear that it meets) at least one design-specific criterion* but has no known “fatal flaw.” |
| Poor |
A study (including meta-analyses or systematic reviews) that has at least one design-specific* “fatal flaw,” or an accumulation of lesser flaws to the extent that the results of the study are not deemed able to inform recommendations. |
| *General design specific criteria are outlined in Harris et al., 2001. (32) |
| NACI recommendation for immunization: grades |
| A |
NACI concludes that there is good evidence to recommend immunization. |
| B |
NACI concludes that there is fair evidence to recommend immunization. |
| C |
NACI concludes that the existing evidence is conflicting and does not allow making a recommendation for or against immunization; however, other factors may influence decision. |
| D |
NACI concludes that there is fair evidence to recommend against immunization. |
| E |
NACI concludes that there is good evidence to recommend against immunization. |
| I |
NACI concludes that there is insufficient evidence (in either quantity and/or quality) to make a recommendation; however, other factors may influence decision making. |
