What do systematic reviews say?

Inactivated influenza vaccine vs placebo or no intervention

Inactivated parenteral influenza vaccine showed no clear difference in hospitalisations Timing of assessment: single influenza season compared with placebo or 'do nothing' (low certainty).

• Vaccines for preventing influenza in healthy adults 2018 · Cochrane Headline outcomes only
  RR 0.96 [0.85, 1.08]
  3 studies · 11924 participants
  Low