The third dimension is us slowing down the spread of the virus. It doesn't necessarily prevent people from ultimately getting sick, but spreading it out ensures that the medical infrastructure is not overwhelmed. If we do nothing to stop the spread, we won't have the infrastructure to handle it and many patients with potentially recoverable ailments (not just corona related issues) will end up receiving subpar care and dying.

I don't understand the first sentence of text.

"The coronavirus can possibly infect a lot more people than there are those who can provide medical care."

Well yes, obviously!

(I assume they meant the virus can infect more people then can be provided medical care during infection).