FROM the beginning of the Covid vaccine rollout, the issue of virus transmission has loomed large as the major unanswered question of clinical trials.

While the primary goal of the immunisation programme has been to prevent severe disease, cut deaths and allow the NHS to refocus on non-Covid care, the possibility that vaccination could also shield people from becoming infected at all - and therefore being able to pass the virus on - would be an important bonus to speed up the return to normality.

Happily, new research from Oxford University and the Office for National Statistics has gone some way to proving that a single dose of Covid vaccine is indeed slowing the spread of the virus - apparently substantially.

It comes just as Scotland prepares for a partial reopening of hospitality on Monday - mainly outdoors - along with the return of shops, swimming pools and gyms.

This will be the biggest test to date of the balance between the virus and the vaccines.

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Other than a plateau in cases during March, possibly linked to more socialising among adults after primary schools returned, the trajectory has been steadily downwards.

Cases have fallen more than ten-fold, from an average of 2,354 per day in January to 218 now; hospitalisations for Covid are down 94 per cent over the same period, from 198 to 12 per day; and deaths have dipped to 0.9 per day - the first time since mid-September that the average daily mortality has been below one.

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The Herald: Average daily Covid cases (top) and confirmed deaths (bottom) have been falling steadilyAverage daily Covid cases (top) and confirmed deaths (bottom) have been falling steadily

Increased travel and mixing over the coming weeks - especially indoors in homes, pubs, restaurants, shopping centres and leisure venues - is expected to push up infections as more unvaccinated people in particular interact.

Some scientists predict a surge in cases - others "a ripple".

The fact that vaccines appear to be curbing transmission, however, should buy us a bit more time and leeway.

According to the Oxford University-ONS study, which analysed Covid rates among 370,000 people during the first four months of the UK vaccine programme, a single dose of either vaccine was enough to cut the risk of infection by 65% from three weeks after vaccination.

Infections with symptoms fell by 74% and asymptomatic infections by 57% .

Those who tested positive after vaccination - without displaying symptoms - also had much lower viral loads, however, suggesting that their chance of passing it on was still comparatively low.

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Both vaccines were found to be just as effective against infections among the over-75s and those with underlying health conditions as in other groups.

People who had received a second Pfizer dose were 90% less likely to be infected (there was insufficient data on second doses of the AstraZeneca vaccine due to its later rollout).

The study - one of the largest to date - is still to be peer-reviewed, but researchers caution that it should also remind us that vaccines are not a complete barrier to infections.

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Until a much larger proportion of the population is fully vaccinated, they would expect some level of social distancing, limits on household mixing, and the wearing of facemasks to continue.

To date, 61% of the adult population in Scotland has had one dose, with only one in five adults fully vaccinated.

Other countries, further behind with vaccines, are finding temporary solutions.

How well the virus transmits in indoor and outdoors setting - and what measures might be put in place to minimise this - is a key focus.

Dutch scientists at the Fieldlab Evenementen have led the way with its Back to Live test series, which trialled seven 'mass gathering' events including a business conference and a cabaret-comedy show with 500 guests in February, and an outdoor music festival with 1500 people in March.

Attendees underwent PCR tests 48 hours before, with random rapid-testing on arrival, and were asked to wear face coverings - but not to socially distance.

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Of the the 6,200 people at all six indoor events (the outdoor music festival results are still pending), five people tested positive within five days of attending - but it is impossible to say exactly where they picked up the virus.

The conclusions of the study - that indoor seated events such as concerts, or (as is being tested in the UK) snooker tournaments - could be safely staged at 50% capacity as long as visitors are tested beforehand and wear masks when walking around the venue is the basis for the policy now being adopted by the government in the Netherlands.

The Herald: Dutch PM Mark Rutte said the country's plan to open up was a 'calculated risk'Dutch PM Mark Rutte said the country's plan to open up was a 'calculated risk'

Museums, casinos, zoos, theatres, the Keukenhof flower gardens and the Efteling amusement park are opening to a limited number of people, and 7,500 football fans will be able to watch Ajax take on AZ Almaar in Holland tomorrow.

Entry to all sites is dependent on proof of a negative test, but the policy - which is coinciding with a reopening of outdoor cafes and an end to curfews - is not without controversy at a time when the Netherlands is experiencing higher rates of Covid than many of its neighbours, including Germany, France and Belgium.

The Herald: The Netherlands is opening up despite averaging 486 cases per million people per day. That compares to 134 and 37 per million, per day, in Denmark and the UK respectivelyThe Netherlands is opening up despite averaging 486 cases per million people per day. That compares to 134 and 37 per million, per day, in Denmark and the UK respectively

On Tuesday, Dutch Prime Minister Mark Rutte said they were taking a "calculated risk" and that hospitalisations had levelled off.

Meanwhile, Denmark - whose infection and deaths rates are among the lowest in Europe - is tackling transmission through its coronapas app scheme.

The digital 'passport' limits entry to public spaces such as zoos, restaurants and hairdressers (but not shops) to those with proof of a recent negative test, vaccination certificate, or a confirmed Covid infection two to 12 weeks previously, uploaded onto the coronapas app. A paper version can also be used.

Around a fifth of Danes have had one vaccine dose and the country has one of the world's highest Covid testing rates, with citizens encouraged to get checked twice a week at free drop-in centres.

Lars Sandahl Soerensen, chief executive of the Confederation of Danish Industry, said: "It's an extraordinary tool, in an extraordinary situation.

"The alternative at the moment is not opening up."