No, it is not necessary to have health insurance to receive a B1/B2 visa. It is not on the list of documents required. I can't find anything specific on the Bern embassy's website, but according to the London embassy, in their non-immigrant visa FAQ:
Visitors and temporary residents are required to pay their own medical costs. As a result it is advisable to take out health insurance.
That is to say, you can be a visitor without health insurance. It may end up being expensive for you, however, if you are uninsured and do need medical treatment while there.
If you already expect to need medical treatment on your trip, and this fact comes up during the interview, perhaps your insurance (or lack of it) could be considered relevant to evidence of
Your ability to pay all costs of the trip.