What comes next, now that the transmission rate and prevalence of Covid-19 have fallen significantly?

(Before you shout at me, yes I know there is frustration and some bemusement among scientists that illness incidence and numbers of deaths have not dropped faster in the UK, but they have nonetheless reduced significantly, if not uniformly, everywhere)

There are detailed plans from the government for when and how to restart certain businesses and social activities in the coming six weeks.

But there is not a clearly articulated strategy for how we are expected to live and work between now and the end of the year (and beyond).

So I've tried to piece together what ministers and officials have said privately and publicly about different elements of the longer term strategy.

Everything rests on a tripod:

1) The growing optimism that a vaccine may be ready for mass use, perhaps as soon as September.

2) The hope that testing, tracing and isolating the symptomatic and their contacts will continue to suppress the incidence of the ghastly virus.

3) The associated hope that the new testing-and-tracing infrastructure will yield reliable data such that if there is a flare up of infections, the response can be a highly localised lockdown (perhaps locking down just one hospital at a time or a small residential community) rather than a regional or national lockdown.

Underlying all policy is the working assumption of the PM, health secretary and their expert advisers that - all other things being equal - there will be a significant second wave, probably from October onwards.

How so?

Well, as a nation we are a world away from that notorious herd immunity, the proliferation within the vast majority of us of antibodies conferred by having suffered the bug or having been injected with vaccine or anti-body rich plasma (and yes I am aware that scientists don't even know for sure whether antibodies confer any kind of helpful immunity - though it would be odd if they gave no protection).

So collectively we remain acutely vulnerable to infection.

However, there seems to be a seasonal element to the rate of transmission, though the significance of seasonality is disputed.

The important point is that as it gets colder, we will as usual move in doors, where it is easier to pick up the infection.

Also the sun's UV seems to be a useful disinfectant.

Which is not to say a second winter spike will be as devastating as what we've been living with.

Because when there is another surge of infection, enough of us may have semi-permanently altered our behaviour enough to keep the R - the rate of transmission - lower than it would otherwise be.

I can see this in my own actions. I now instinctively socially distance and I have no problem wearing a mask when in a confined space (confession: I was always a neurotic hand-washer).

Like most of us, I miss hugging family and friends, but the price of hugs seems exorbitant.

Even so, however much we alter our social interaction at work and play, it is probable that the virus will remain a real and present danger.

So let's look at the detail of Boris Johnson's planned prophylaxis.

First, there is much more optimism around the possible availability of a vaccine as early as September than seemed remotely plausible only a few weeks ago.

The developers - the researchers at Oxford University and its commercial partner, AstraZeneca - put the probability at "much greater than 50% that the vaccine is active", in the words of one of those intimately involved in the project.

The uncertainties include what kind of protection the vaccine may give.

There is for example too little evidence on whether it would eradicate the virus from the body entirely or do the lesser job of reducing the severity of the illness, so that hospitalisation is less of risk.

Either sort of shield would of course be preferable to our current lack of any viral defence.

It is also unclear whether we would need one or two doses.

None of which is to say we won't all feel bitterly let down at the end of July, which is when the Oxford/AZN vaccine team think they will know with more confidence whether they have a winner.

Apart from anything else, the more that lockdown and sunshine reduce the spread of the virus in Europe, the harder it is for the researchers to conduct robust trials on humans.

Those trials need to take place where there is enough of the illness passing from person to person for meaningful comparisons to be made between the health outcomes of those who've been vaccinated and the unvaccinated.

That is why AZN and Oxford are rapidly setting up a study in Brazil, where Covid-19 is still raging.

What if the vaccine is a pharmacological lemon? Will it be back to full national lockdown when the frost bites?

That is not Johnson's and Hancock's plan or hope.

A second national lockdown could in theory be avoided if the bold new test-trace-and-isolate infrastructure actually works and turns out by September to be the world class system that has been promised by its creator Dido Harding.

The logistical challenge of creating such an alert-and-extinguish system is not to be under-estimated however.

Apart from anything else, speed and comprehensiveness of coverage are absolutely of the essence.

Let's examine just one part of the design, namely the PM's pledge from this week that all tests that aren't subject to the vagaries of the postal system should be completed in 24 hours.

There are plenty of epidemiologists who are anxious that is not adequate, simply because - on the basis of current performance - more than a third of the relevant tests are subject to the postal system (tests that are carried out at home or at mobile sites) and therefore will take longer than 24 hours.

Here is the potentially lethal maths of testing delays.

Let's say you acquire the symptoms and you immediately order the test to be done at home.

It may arrive the following day, or maybe the day after. Then you swab yourself and send it back. It could take another couple of days to reach the lab. And then another day to be processed by technicians.

You would get the result perhaps six days after you acquired the symptoms, perhaps even later than that.

During all that time, you will have been isolating at home with your family.

So in theory you won't have been spreading the virus directly beyond those with whom you share your home.

But - and this is what matters - it is only after you receive a positive test that the government's newly employed teams of virus tracers will attempt to contact all those people you were infecting in the days before you went into quarantine.

And if any of them were infected by you, they will have been out and about in the community infecting others for several days.

This is why the former health secretary, Jeremy Hunt, has been loudly pressing the government to adopt Taiwanese standards of testing turnaround times, a day or less.

It is hard to challenge his logic that a potential lag of several days between someone needing a test and the start of contact tracing means the risk of infection within the community will remain far too high.

By the way, it also seems eccentric that the rules allow those with symptoms to allow resumption of normal life if they receive a negative test, since false negatives from the tests are in the 20% to 30% range.

Far better, as Hunt said on my show the other night, to at least require those with the classic symptoms to have a second test, before they are allowed to leave home and re-enter the workplace, which obviously include hospitals and care homes.

Equally there is an argument for mandatory weekly testing of everyone working in care settings - hospitals and care homes - given the high prevalence of the virus in those places.

That kind of mass testing is being promoted by Tony Blair and Gordon Brown, and we are yet to have a proper debate about the Paul Romer argument that unlocking the economy can only safely be done when literally all of us are regularly tested.

All of which is to argue that the risk of a second viral surge does not bring a commensurate risk of a second national lockdown.

But it is to say that to avoid such a lockdown, which would wreak utter havoc on our way of life and incomes, a mind-numbing amount of complex work, on detecting the virus and vaccinating against it, has to be completed successfully in record time.

Even with the most competent leaders and officials in history - and we probably lack those - there is no guarantee enough will go right.