Table 1 Methods used to evaluate the VE against persistent infections and analyses from included studies

- Observational [13, 14]

- Experimental [13, 16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40, 42,43,44,45,46]

- 2 consecutive measurements positive [13, 16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40, 42,43,44,45,46].

- 2 consecutive measurements: positive preceded by a negative measurement [14]

- Sequence of positive measurements over a certain time span [18, 41]

- 6 months^a [17, 20, 22, 25, 26, 28,29,30, 34,35,36,37,38,39, 43, 44, 46]

- 12 months^a [13, 14, 27, 40]

- 6/12 months^a [16, 18, 19, 21, 23, 24, 31,32,33, 41, 42, 45]

- Conditional exact for comparing two independent Poisson rates using a binomial distribution (14,15,24–28 [39, 41–43] ,16, 35–44,17–23)

- GEE Poisson [13, 40]

- Cox Proportional Hazard [22, 38]

- Prentice Williams Peterson total time approach [14]

- Number of cases/number of participants [17,18,19, 21, 22, 25, 27, 31,32,33, 38, 41,42,43,44]

- Number of cases/person years at risk [13, 14, 16, 20, 23, 24, 26, 28,29,30, 34,35,36,37, 39, 40, 45, 46]