What do systematic reviews say?

Inactivated influenza vaccine vs placebo or no intervention

Inactivated parenteral influenza vaccine leads to higher fever assessed by subjective report Timing of assessment: single… compared with placebo or 'do nothing' (high certainty).

• Vaccines for preventing influenza in healthy adults 2018 · Cochrane Headline outcomes only
  RR 1.55 [1.26, 1.91]
  13 studies · 23850 participants
  High