[chiralSPO (OP)]

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This data (screen grabbed from the New York Times just now) clearly shows a periodic (possibly sinusoidal) variation in new cases reported each day. The period appears to be is exactly 7 days (1 week). With maxima coming on consecutive Fridays (with the occasional Thursday).

I see a few possible explanations:
1) This is an artifact caused by weekly patterns in data reporting (file the report by the end of the week.)
2) This is an artifact caused by when it is easiest for most people to get the tests.
3) This is real and represents a weekly pattern in when people get sick (maybe folks go out Saturday night, get infected then, and then feel bad enough to get tested 6 or maybe 5 days later.
4) This is real and represents ripple effects of more people get infected when there are more infectious people around, and because of the induction period there are actually bulges that propagate at a period of about 1 week.
5) something else?

Looking at the deaths graph offers more insight:

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1) is challenged by the fact that the reported deaths, although also following a weekly periodic undulation, peak on Wednesdays. (presumably there would be similar reporting biases)
2) is also not supported by the deaths graph (people don't tend to only die when it is convenient)
3) could be supported, if the length of time from showing symptoms to death is fairly consistent (and not supported if it varies widely)
4) see above
5) ??

[Bored chemist]

is also not supported by the deaths graph (people don't tend to only die when it is convenient)

No, but they report deaths when it's convenient.

I think the underlying cause is a combination of 1 and 2.

3 Has 2 problems- many or most people are as likely to get infected at work as on a saturday night.
The incubation period is rather variable.
Re. 4- it's about a week, but not exactly a week, which is what would be needed to produce that graph.

5- well it could be.

But death rates always follow this sort of trend- they did it before covid was here.

[alancalverd]

Since the initial symptoms are mild, most people will finish a week's work  before reporting for testing. Hence the Friday peak in reported cases.

You can assume that very little paperwork gets done at the weekend. The cause of death must sometimes be verified by a consultant if the initial certificate was issued by a junior doctor, but Friday is golf day and committees pray together (IIRC they have no other useful function) on Mondays. Most jurisdictions allow 3 to 5 days to record a death, so Wednesday is the day for reporting known COVID deaths.

These graphs underline how the conflation of delayed symptoms and political stupidity have led to the dominance of  this interesting virus over all human thought and action.

[Bored chemist]

have led to the dominance of  this interesting virus over all human thought and action.

In your imagination perhaps.

Must of us are still working (I'm having a coffee break).

[alancalverd]

Has absolutely nothing in your life changed? I doubt it, unless you are a hermit with a self-sufficient smallholding (or an Ocado account*) and no friends. Everyone else in the developed world (i.e. excluding the USA) has had to adjust in some way, and most of Africa is catching up.

Whilst US citizens have mostly gone about their daily lives shooting one another and praising the Lord, a considerable number (as reported by the OP) have coughed, lost their jobs, been shot for wearing/not wearing a mask,  or died, and the bars in Texas and Florida are losing money.

*come to think of it, the nice young men who wash your helicopter while you shop at Waitrose, no longer valet the interior, so nobody is completely unaffected.