Nicola Sturgeon has cut Scotland’s self-isolation period from 10 to seven days, after sustained pressure from businesses and opposition parties to address soaring staff absences.

The first minister told MSPs on Wednesday her government’s highly cautious stance on the 10-day isolation period was being softened after data from hospitals suggested the Omicron variant was less medically severe than feared.

Sturgeon also confirmed Scotland would adopt a new rule on taking PCR tests announced in England earlier on Wednesday, to cut the number of PCR tests being taken unnecessarily and to conserve supplies.

She said the requirement for someone with a positive lateral flow test to immediately book a PCR would be dropped, as long as they did not have symptoms. That new rule will come into force on Thursday 6 January, rather than 11 January as in England.

Ministers in England and in Wales cut self-isolation to a week in December after deciding the impact of extended self-isolation on public services and businesses was not outweighed by Omicron’s risk to health and critical care services.

In a recalled session of the Scottish parliament, where she faced heavy criticism over the quality of NHS data in Scotland, Sturgeon said adults could end their self-isolation after seven days if they had no fever and had had two negative lateral flow tests.

Close contacts will not have to self-isolate if they are fully vaccinated, have no symptoms and record negative tests every day for seven days, under new rules which take effect from midnight on Wednesday. Anyone not fully vaccinated will need to remain in isolation for 10 days – a measure expected to drive up vaccination rates.

She acknowledged the new rules were “more proportionate and sustainable and less restrictive”.

Sturgeon’s move came after Scottish hospitals said their services were under significant strain because of staff absences. The train operator ScotRail cut hundreds of services this month owing to staff shortages. Hospitality companies and retailers have struggled to stay open, and have complained bitterly about the impact on their businesses.

While Scotland has recorded its highest-ever Covid infections – 20,217 on Monday, a figure partly inflated by results delayed by the holiday weekend – rates of critical illness have remained stable.

There were 1,223 people with Covid in hospital on Wednesday, more than double the number seven days ago, but the number in intensive care remained stable, at about 52 or 53 people a day. Five more people had died after a positive Covid test, taking the total under that measure in Scotland to 9,872.

The first minister came under pressure from opposition parties over the quality of government data after it emerged that John Swinney, her Covid recovery minister, had used old survey figures to defend Scotland’s restrictions.

Douglas Ross, the Scottish Conservative leader, said Swinney had used “misleading data for scoring petty political points” on Tuesday after he quoted Office for National Statistics survey results from mid-December to claim infection rates in England, at 1 in 20, were twice those in Scotland, at 1 in 40.

Sturgeon confirmed the latest ONS data showed Scotland’s estimated infection rate was 1 in 20 last week, compared with 1 in 15 for England. English regional data was more varied, from 1 in 10 in London to 1 in 30 in other regions. It was 1 in 25 in Northern Ireland and 1 in 20 in Wales. She denied Swinney had used misleading figures but acknowledged “this isn’t a competition”.

Sturgeon was warned by Alex Cole-Hamilton, the Scottish Liberal Democrat leader, and Jackie Baillie, deputy leader of Scottish Labour, that she risked losing political support unless the quality of the evidence she relied on improved.

They said Swinney had also wrongly promised new data would be published on Wednesday to show how many patients were admitted because they had Covid, rather than for other medical reasons.

Public Health Scotland said it hoped the figures would be released on Friday. English data suggests a third of Covid-positive patients were hospitalised with other medical complaints.

“Transparency has ebbed away,” Cole-Hamilton said.