A common cold literature review mentions the RSV vaccine trial, Vit C, Echinacea and zinc

From a 2004 review of the common cold.  This paper says 10-15% of colds are due to coronaviruses.  Some suggest a higher percentage.  It can be useful to read literature that is untainted by current political considerations.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7125703/

The development of an RSV vaccine has been hampered by the experience with formalin-inactivated whole RSV vaccine in the 1960s, as it caused 80% of RSV vaccinees to become hospitalised compared with 5% of controls, as well as two fatalities [80]. Current major research has focused on a prophylaxis using a humanised mouse monoclonal antibody, Palizivumab, which has been shown to reduce the rate of RSV-associated hospitalisation in premature infants [81]. However, its use on a wider population will require further research.

There is currently no licensed Parainfluenza vaccine to date. The formalin-inactivated vaccine generated in the 1960s was not able to prevent PIV infection and was soon abandoned. At present, recombinant bovine PIV3 and human PIV3 attenuated vaccines are being evaluated in animal models as vectors for the delivery of other viral antigens such as RSV-G and RSV-F proteins. This bivalent vaccine combination provides a high level of resistance to challenge with PIV3 and RSV in animal models [82].

The conventional methods of vaccination are via the intramuscular and subcutaneous routes. Mucosal immunisation has recently been explored and represents an attractive manner of delivering vaccines. It is fast, simple and noninvasive, and it can be carried out by unskilled individuals. The use of mucosal vaccination seems logical in that most respiratory viral infections initially start at the mucosal sites. Therefore, inducing local immunity can help arrest the infection at an early phase before systemic complications arise.

Thus far, there has been inconclusive evidence to support the use of vitamin C and extracts of the plant Echinacea in common cold prevention. Daily supplementation with large doses of vitamin C does not seem to prevent common colds; however, there seems to be a modest (8–9%) reduction in the number of symptom days in individuals with established cold symptoms, with larger doses having a greater effect [83]. For Echinacea, currently available data from studies conducted in the adult population show positive findings both in the treatment and prevention of upper respiratory infection. However, variations in the design of the clinical trial and in Echinacea preparations have to be taken into account [84].

Zinc has been shown to possess antiviral properties in vitro, and different preparations of zinc have been proposed for the treatment of the common cold. Zinc lozenges appeared to have positive effects on adults, but negative effects on children in terms of duration and severity of common cold symptoms [85], [86]. Zinc nasal spray appears to reduce the total symptom score but has no effect on the duration of the common cold [87]. Recent research shows that zinc nasal gel can reduce the median time to cold resolution compared to placebo (4.3 days vs. 6.0 days; p=0.02) and decrease the median time to resolution of nasal congestion, nasal drainage, hoarseness and sore throat [88].