Zinc for the Common Cold
Studies have found that zinc lozenges may reduce the duration of cold from a median of 7.6 days to 4.4 days.
Sambucus Elderberry for the Flu
Elderberry - Elderberries are thought to prevent or shorten the duration of herpes outbreaks, decrease pain and inflammation, and reduce symptoms of upper respiratory infections. Many people consider the elderberry plant one of the most powerful for preventing and treating colds and influenza and swear by its antiviral properties. One placebo controlled study found an improvement in 2 days in 93.3% of subjects using elderberry syrup compared to 6 days in 91.7% of subjects that received a placebo.
Vitamin C has been studied for many years as a possible treatment for colds, or as a way to help prevent colds. A meta-analysis found that vitamin C (1-6 g/day) decreased the duration of the cold episodes by 0.93 days.
Immune Boosting Probiotics
The combination of Lactobacillus acidophilus and Bifidobacterium animalis lactis probiotics by children during winter months has been found to reduce fevers by 53%, coughing by 41.4%, runny nose by 28.2%, antibiotic use by 48%, and reductions in days absent from group child care when compared to placebo.
Sambucus Elderberry: https://www.ncbi.nlm.nih.gov/pubmed?Db=pubmed&Cmd=ShowDetailView&TermToSearch=9395631
Vitamin C: https://www.tandfonline.com/doi/abs/10.1080/07315724.1995.10718483