Key Takeaways

Absolute vaccine benefits depend on the population and season. Supplement claims also need to distinguish prevention from treatment.

The 2018 Cochrane review found that inactivated influenza vaccines reduced confirmed influenza from about 2.3% to 0.9% in healthy adults. Those averages came from older trial seasons. [1]
German vaccination recommendations depend on age, pregnancy, medical risk and exposure. A healthy-adult trial average cannot replace those distinctions. [2]
Cold prevention and treatment are separate questions. Zinc treatment may shorten symptoms, with uncertain evidence and adverse effects. [3]

Download the evidence pack (Markdown) ↓

Common questions

What does the flu vaccine’s absolute benefit mean?

The review estimated that about 71 healthy adults would need vaccination to prevent one confirmed influenza case. Evidence for hospitalization and work absence was uncertain. Seasonal effectiveness and individual risk vary. [1]

Who is covered by the German flu recommendation?

STIKO recommends vaccination from age 60 and for specified risk groups. Pregnancy is included from the second trimester, or the first with an underlying risk condition. Medical and occupational indications require the current RKI guidance. [2]

Is working through a respiratory infection a good default?

RKI advises staying home for three to five days and until symptoms have clearly improved, with particular care around people at higher risk. Worsening symptoms or increased medical risk warrant contact with a clinician. [4]

Does regular vitamin C prevent ordinary colds?

The Cochrane review found no meaningful reduction in general-population incidence. Regular supplementation modestly shortened duration. Starting vitamin C after symptoms began produced no consistent benefit in the trials reviewed. [5]

Does vitamin D prevent respiratory infections?

The 2025 meta-analysis did not establish a statistically significant overall preventive benefit. That question is separate from treating diagnosed deficiency or other established indications. [6]

Can zinc shorten a cold?

The 2024 Cochrane review estimated roughly two fewer days, with low-certainty evidence and substantial variation. Non-serious adverse effects increased. The pooled result does not establish one standard product or dose. [3]

Which throat symptoms need urgent care?

A rapidly worsening severe sore throat with mouth or throat swelling, difficulty breathing, inability to swallow, difficulty speaking or opening the mouth needs emergency assessment. These symptoms can occur with a tonsillar abscess. [7]

Winter Infections, Flu Vaccines and Supplements