IF you experienced a strange sense of déjà vu on Tuesday, you probably weren't alone.

Nearly six months to the day since Boris Johnson took to our screens to tell Britain to "stay at home", we find ourselves once again facing tightened restrictions - albeit this time couched in terms of avoiding a second lockdown.

Then, as now, the "critical thing" is to stop the disease spreading between households.

In Scotland, this means a nationwide ban on visiting other people's homes and continued 'rule of six' limits on how many people can meet together outdoors or in hospitality venues.

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A surveillance report by Public Health England shows that the vast majority of contacts traced for each new positive case were either people the person lived with (57 per cent) or visitors to the household (13.5%).

That means that the home is also the most likely source of exposure - followed by leisure and community venues such as restaurants, pubs, gyms, playgroups, cinemas and places of worship, which accounted for only around 7% of contacts (and potential sources of infection).

Such a breakdown of Test and Protect data for Scotland is not yet available, but it is likely to be very similar, underlining the puzzling decision of the UK Government not to impose household visiting bans on England - something ministers there may U-turn on shortly.

In any case, it explains why - for now at least - schools, hairdressers and shops remain open, with pubs and restaurants continuing with a 10pm curfew from tomorrow: they are not the major transmission zones.

Schools are problematic because children are super-spreaders of cold and flu bugs which can be confused with Covid (hence the spike in demand for testing), while the hospitality sector can reduce risk with strict hygiene, physical distancing, and temperature checks.

The curfew has more to do with curbing late-night inebriation that erodes patrons' compliance, but may in the end backfire if drinkers ignore public health rules to gather at home with friends instead.

Research from the US has shown that universities are hotbeds for Covid outbreaks, however, and this is already beginning to play out in Scotland where single cases in shared halls of residence have led to hundreds of students being asked to quarantine.

Bear in mind that this can mean self-isolating for 14 days in a single room, not a house, and it is easy to imagine how quickly that situation will deteriorate - especially if the cycle is endlessly repeated.

One mother described to me this week how her son - a fresher at St Andrews University who is quarantining after a positive case in his hall - has his meals left outside his room door on a tray and is not even allowed outdoors for exercise.

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He has tested negative so far, but must still complete the full 14 days in case the virus is incubating.

It sounds more like solitary confinement for prisoners.

Plenty has changed since March though, and not only in terms of our knowledge of the virus and how to treat patients.

Back then, we had the capacity to process just 780 tests a day; today it is upwards of 15,000.

Yet we also know from countries such as South Korea that if the test, trace and isolate system is robust enough, full lockdowns can be avoided altogether.

If we have to resort to the "nuclear option" again, it will be a clear signal that our testing capacity has been overwhelmed and our contact tracing too slow (people should receive results within 24 hours).

The fact we are now routinely exceeding 5% percentage positivity for tests is a red flag.

Given that households are also the main source of transmission, quarantine accommodation - such as hotels - should be made available to those who would struggle to isolate properly from flatmates and family members at home, as it has been in other countries.

Despite recent increases in Covid cases, however, hospital admissions remain a fraction now of what they were in March.

On the day that lockdown was announced, March 23, a total of 95 patients with Covid were admitted to hospitals in Scotland. It went on to peak at 213 admissions in a single day on April 1.

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On September 16 - the most recent date for which figures are available - 16 Covid patients were admitted to hospital in Scotland.

Overall, admissions are currently averaging what they were at the very beginning of March: eight per day. This is low, but still up three-fold from 2.5 per day at the start of September.

If, and how quickly, it slows and reverses depends on what happens in the community.

Politicians are gambling that acting at an earlier stage in the epidemic curve with a 'lockdown lite' approach will deliver the same results as before, but potentially more quickly and without re-pausing NHS services.

But with a Covid-weary public and a spike in winter respiratory infections squeezing our testing capacity, it remains to be seen whether history will repeat itself.