What do systematic reviews say?

Influenza vaccine vs placebo

Influenza vaccine showed no clear difference in fever compared with placebo (moderate certainty).

• Vaccines for preventing influenza in the elderly 2018 · Cochrane Headline outcomes only
  RR 1.57 [0.92, 2.71]
  3 studies · 2519 participants
  Moderate

Influenza vaccine vs control

Influenza vaccine may leads to higher fever compared with control (low certainty).

• Influenza vaccines for preventing acute otitis media in infants and children 2017 · Cochrane Headline outcomes only
  RR 1.15 [1.06, 1.24]
  7 studies · 10615 participants
  Low

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

Inactivated influenza vaccine vs placebo or no intervention

The review found no eligible studies for this question.

• Vaccines for preventing influenza in healthy children 2018 · Cochrane Headline outcomes only
  no estimate extracted
  Studies not reported
  No studies found

Live attenuated influenza vaccine vs placebo or no intervention

• Vaccines for preventing influenza in healthy children 2018 · Cochrane Headline outcomes only
  no estimate extracted
  4 studies · 20561 participants
  Very low