My only evidence for that assertion is that soap has killed viruses since its invention. Wikipedia/soap, “The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient Babylon.[11] A formula for soap consisting of water, alkali, and cassia oil was written on a Babylonian clay tablet around 2200 BC.[12]”

Johnson Baby Shampoo is a modern form of soap that is so mild that it can be used on a baby’s skin, and the babies still tolerate it. Although in normal usage, the soap is typically put directly onto a mother’s hand and then, with some water, put directly onto the baby’s skin.

My suggestion is for people with a possible Covid virus in their nostrils to wash their nostrils with diluted baby shampoo. I have been doing this for a year without any problem, even though I have had two Pfizer vaccine shots. It takes only a few seconds, and it clears the nostrils of snot, which may contain viral particles. So even if the soap doesn’t kill the Covid viruses, the washing does wash them away.

The solution I use is even milder than plain tap water. My method is one drop of Johnson’s Baby Shampoo per cup of preboiled water put into a beverage bottle. I pour out a teaspoon of this dilute solution into the palm of my hand and gently sniff it into my nostrils. I gently pinch closed my nose for a few seconds and then forcefully blow out the solution. That’s it.