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Table 2 Separate and joint effects of the preventive exposures “Influenza vaccination” and “OFC” on the risk of ILI after recoding and results of analyses of interaction

From: Do the omeprazole family compounds exert a protective effect against influenza-like illness?

Odds Ratios representing separate effects OR (95% CI)
Non-OFC users 4.38 (2.54 – 7.53)
Users of OFC 1 (reference category)
Not Vaccinated 3.8 (2.15 – 6.71)
Vaccinated 1 (reference category)
Odds Ratios representing joint effects  
OR11 non-OFC users and unvaccinated 5.75 (2.71 – 12.22)*
OR10 non-OFC users but vaccinated 1.48 (0.64 – 3.40)
OR01 users of OFC but unvaccinated 0.92 (0.33 – 2.53)
OR00 users of OFC and vaccinated 1 (reference category)
Measure of effect of interaction on additive scale  
RERI 4.34 (1.46 - 7.26)
  1. *Observed OR = 5.75, while expected OR in the absence of interaction on an additive scale was 1.40, calculated as [(1.48 – 1) + (0.92 – 1) + 1], where 1.48 = OR non-OFC users but vaccinated and 0.92 = OR users of OFC but unvaccinated.