This last week has been a time of stress with the passing of my father-in-law. Besides many hours without sleep, an attending relative also had a bad cold that was coughing over everyone. I started signs of exhibiting a cold. I recalled that infections alter gut-bacteria (in a manner that supplies metabolites that the infection needs), so I decided to try subverting the infection by the use of strong probiotics to out-compete the bacteria that the infection was asking to increase production (via chemical signalling). The symptoms disappeared within 2 hours. Over the following days, whenever signs of a cold appeared I took another significant dosage; the symptoms disappear again.
This seems to be confirmed by the literature:
“A subgroup analysis was performed based on the length of the probiotics administration period. When the period was less than three months, the occurrence of the common cold decreased by 18%, but if it was longer than three months, it had no effect on cold prevention.” 
“A two-strain probiotic combination given twice a day for 3 months was able to reduce the symptoms of the common cold and school absenteeism in schoolchildren.”
- If you take probiotics continuously, the effect is loss. It is the introduction of bacteria that will fight against both the infection bacteria and existing bacteria that results in an effective disruption!
There are a large number of studies on how probiotics improves the immune system with several of them identifying that individual response to probiotics was seen, as well as different impact on different species of the flu. Some had significant effects while other has minor or no effects. So mileage per probiotic may vary greatly.
Which one did I use? It was Mutaflor (E.Coli Nissle 1917) because E.Coli is a dominant species in the human gut (and thus the most likely to be “reprogrammed” by an infection). My #2 choice would be Prescrip-Assist.
Side note: Using standard probiotics does carry a risk of inducing a harmful infection!
The risk is low, 1 in 500 people, as reported by this 2012 study
“The maximum estimated incidence of probiotic-related bacteremia due to L. acidophilus/L. bulgaricus during the 8-year period was 0.2%”