https://www.cherry.co.uk/about-cherry/press/cherry-wetex.html
 
For years, various representative studies have shown that computer keyboards are among the dirtiest and most bacterially contaminated office products available. There are many reasons for this. Firstly there is a high concentration of foreign bacteria on our hands with which we operate the keyboard. Secondly, external influences such as eating and drinking at work, bring further contamination to the keyboard. These impurities often remain hidden as dirt and bacteria collect under the individual keys. Unfortunately, because of this, keyboards are cleaned by their owners far too rarely or only on the surface.

In today's tense times, where special attention must be paid to hygiene, some industrial sectors and branches are confronted with sanitation concepts that sometimes push them to their limits. Especially in organizations with a large number of staff and constant changes of customers or patients, or in production or workshops where liquids, dust, or production waste are generated during work, simple and effective solutions are needed to protect computer keyboards.
 
As the world's leading keyboard manufacturer, CHERRY has reacted accordingly. It has added CHERRY WetEx to its range of products, a protective cover for computer keyboards that prevents dirt from penetrating under the keys of a keyboard, and also can be cleaned without difficulty using standard disinfectants*. This provides simple but effective protection against bacteria, viruses, and other contaminants. In clinics and doctors' offices, for example, the keyboard's entire contact surfaces can be disinfected quickly and easily regularly, which can protect your employees from illness.

WetEx is a flexible protective film which is resistant to diesel, oil, detergent, and distilled water as well as conditionally resistant to petrol and 40% sulphuric acid. It fits perfectly over the keyboard and offers an impenetrable surface. Under normal conditions, WetEx will last >10 million operating cycles and is ideal for home, office, and industrial applications.

WetEx has been developed for a wide range of CHERRY products, including the KC 1000, G84-4100, KC 1000 SC, and STREAM KEYBOARD models. It is easy to handle and provides comprehensive protection for the keyboard within seconds. Because CHERRY always takes the environmental aspect into account in its products, WetEx is free from halogens and latex and does not contain polybrominated diphenyl ethers. No polybrominated dibenzodioxin or dibenzofuran is produced during disposal.

The CHERRY WetEx keyboard protection is available immediately starting at a recommended retail price of 30 USD.
 
I think 30 dollars is a bit high but if you value a clean working environment then maybe the cost is not important.