I thought "plague" was a generic word for a disease. I was corrected earlier when talking about COVID that it is a virus not a plague. I am aware it is a virus. But would it be wrong to say "We live in a time of plague" or something similar?
"Plague" can have several different meanings depending on context:
In its most technical form, "plague" is used to refer specifically to diseases caused by the bacterium Yersinia pestis (e.g. "bubonic plague", "pneumonic plague", etc). This has historically also been known by names such as "the black death", etc. In this sense, COVID-19 is definitely not a form of "plague", because it is not caused by that bacterium (it is not caused by bacteria at all, as it is a viral disease).
In a more general sense, "plague" is sometimes used to refer to any disease which is widespread and has a fairly high mortality rate. In this sense, COVID-19 could potentially be considered "a plague", except that its mortality rate is still relatively low compared to most other things that have been called "plagues" in the past, so most people probably wouldn't consider it to meet the criteria (at least not yet).
In a looser, often joking way, some people will refer to any widespread disease currently going around (such as a flu) as "the plague". This use is not generally intended to be taken literally but is just a form of hyperbole.
Occasionally, "plague" is also just used as a general synonym for "widespread disease", but this is generally only used in a literary or highly metaphorical context. In this sense, you could actually say "We are living in a time of plague" to mean simply "We are living in a time of widespread disease" (without really talking about COVID-19 specifically, though it may be implied).
(It's worth noting here that I've only covered senses of the word "plague" that have to do specifically with diseases. The word does have other meanings as well, which are not necessarily tied to disease (e.g. "a plague of locusts"), but in the context of the original question, I believe these are the relevant ones.)
A plague is a general term for an outbreak of a virulent disease. Or even more generally, any outbreak of something unpleasant.
For centuries smallpox was one of the world's most-dreaded plagues, killing as many as 30 percent of its victims.
A plague of flies descended on a Russian village after farmers used chickens droppings as fertiliser.
The word has a biblical origin, being used in the Latin bible to translate the Hebrew word for the afflictions that God sent to Egypt at the time of Moses. (The ten plagues of Egypt)
But plague is also the name of a particular disease, caused by the bacteria Yersinia pestis. It was the cause of the black death in Eurasia and North Africa. (note that plague killed about 60% of victims)
Plague can be treated by antibiotics.
Yes, you can use plague as a “general” term.
It is also usable (as The plague) to refer to the particular disease as noted already.
Without the the, it means anything that (a) afflicts, (b) besets and (c) in general is a nuisance i.e. irritating, persistent, and / or widespread.
It's often found in compound terms, such as [place] was plagued with [pest] (e.g. Seventeenth Century London, rats; Westminster, politicians — or if you are a politician, then you might say it's plagued with journalists, civil servants and other people asking awkward questions, or possibly giving awkward answers).