It is commonly thought that colds and flu are highly infectious diseases and indeed that this is the only way that they can be ‘caught’. However, attempts at proving this in clinical trials have invariably failed.
Milton J Rosenau
Milton Rosenau tried to spread Spanish Flu from one person to another but failed.
“In March of 1919 Rosenau & Keegan conducted 9 separate experiments in a group of 49 healthy men, to prove contagion. In all 9 experiments, 0/49 men became sick after being exposed to sick people or the bodily fluids of sick people.”
In November 1919, 8 separate experiments were conducted by Rosenau et al. in a group of 62 men trying to prove that influenza is contagious and causes disease. In all 8 experiments, 0/62 men became sick. Another set of 8 experiments were undertaken in December of 1919 by McCoy et al. in 50 men to try and prove contagion. Once again, all 8 experiments failed to prove people with influenza, or their bodily fluids cause illness. 0/50 men became sick.
https://jamanetwork.com/journals/jama/article-abstract/221687
Others
More failed attempts to spread colds and flu and some reportedly successful ones. However keep an eye out for experimenters ‘inoculating’ patients with nasal secretions – this is a somewhat vague term which likely involves deliberate damage to the mucous membrane and is not, in any case, the way that disease is said to proliferate.
In 1919, Wahl et al. conducted 3 separate experiments to infect 6 healthy men with influenza by exposing them to mucous secretions and lung tissue from sick people. 0/6 men contracted influenza in any of the three studies.
https://www.jstor.org/stable/30082102?seq=1#metadata_info_tab_contents
In 1924, Robertson & Groves exposed 100 healthy individuals to the bodily secretions from 16 different people suffering from influenza. The authors concluded that 0/100 became sick as a result of being exposed to the bodily secretions.
https://academic.oup.com/jid/article-abstract/34/4/400/832936?redirectedFrom=fulltextA
In 1937 Burnet & Lush conducted an experiment exposing 200 healthy people to bodily secretions from people infected with influenza. 0/200 became sick.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2065253/
In 1940, Burnet and Foley tried to experimentally infect 15 university students with influenza. The authors concluded their experiment was a failure.
https://onlinelibrary.wiley.com/doi/abs/10.5694/j.1326-5377.1940.tb79929.x
‘In 2003, Bridges et al reviewed influenza transmission and found “no human experimental studies published in the English-language literature delineating person-to-person transmission of influenza.”‘
https://virologyj.biomedcentral.com/articles/10.1186/1743-422X-5-29