Northern Ireland’s chief scientific adviser has warned of the risks of complacency after Covid-19 cases in the region increased rapidly last week. Professor Ian Young said it was “inevitable” that there would be a significant increase in coronavirus cases if people stopped following social-distancing rules designed to prevent the spread of the disease.

The reproduction rate of the virus is estimated at between 1.2 and 2.0, according to Northern Ireland’s Department of Health. There were 242 cases last week, with 74 positive tests announced on Friday alone – only 237 people tested positive during the whole of July.

“We’ve just had probably two months with very little evidence of the virus,” said Young, who also sits on the UK government’s Scientific Advisory Group for Emergencies. “No deaths for maybe 18, 20 days in a row; very few patients in hospitals. In that setting, it’s really hard for people to remember the importance of [social-distancing] behaviours. People relax, and they go back to what we still think of as normal. And if that happens, then it’s inevitable that we will see a further surge or significant increase.”

With the reproduction rate well above 1.0 – the critical number at which virus infections start to rise exponentially – the Stormont executive has deferred further relaxations of lockdown, including drinking-only “wet” pubs.

“I absolutely share politicians’ concern about the situation,” Young said. “That’s why I’m hesitant to say we have done well. We are still at an early stage in this epidemic. In two months’ time, I would be in a better place to see if the measures we’ve taken are effective.” A return to full lockdown would be “a fairly disastrous outcome”, he added.

Covid-related deaths were substantially lower in Northern Ireland than in the rest of the UK during the height of the crisis. An Office for National Statistics comparison of death rates across Europe found England had the worst figures, at 38.8 deaths per 100,000 people in the week of 11 April. Northern Ireland’s peak came a week later, with 28.8 deaths per 100,000 – worse than France, Denmark and Norway, but better than Belgium, the Netherlands, Hungary and anywhere else in the UK.

The one-week gap between England’s peak death toll and Northern Ireland’s may provide a clue as to why the region fared better. Northern Ireland’s first community case of Covid-19 was identified the day before the UK-wide lockdown was introduced on 23 March, whereas community transmission was widespread in England by the time Boris Johnson issued the order to stay at home.

“By the time lockdown came, we were at a much earlier stage,” said Dr Gerry Waldron, head of health protection at the Public Health Agency, which runs the contact-tracing service. “For us, lockdown came at probably the right time.”

Geography is another factor. Northern Ireland’s 1.9 million population live mostly in rural areas, with about 340,000 people in Belfast. The city’s public transport system is a cause of regular complaint, and commuters often drive, enabling better social distancing.

The Troubles may have helped, according to Dr Anne Campbell, a senior lecturer in social work at Queen’s University Belfast. “After 50 years living through conflict and post-conflict politics, people are more politically discerning,” she said. “They see through rhetoric while conversely believing in facts and logic. That is why I feel people here listened to the chief medical officer and the other scientists right from the start of lockdown and obeyed the rules.”

Republican and loyalist community associations in north Belfast had worked together to help vulnerable people affected by Covid, she added.

Political decisions were taken swiftly and with an unusual degree of cooperation between the Democratic Unionist party and Sinn Féin, and health minister Robin Swann of the Ulster Unionist party.

While health services in England were focused to a large extent throughout April on meeting the target of 100,000 daily tests set by Matt Hancock, the health secretary, the same period in Northern Ireland was spent on expanding the contact-tracing team.

Northern Ireland’s Test, Trace and Protect service has reached up to 98% of people who came into contact with a positive case, while England’s remains below 80%. Staffed by healthcare professionals rather than lay call-handlers, Test, Trace and Protect has identified 11 clusters of cases, including a karaoke party where a shared microphone is believed to have led to the outbreak.

A quarter of a million people have downloaded the StopCOVID NI exposure-tracking app, which went live two weeks ago. England launched a pilot scheme of its second version of an app last Thursday.

Public Health England has been under pressure for some time from Tory MPs who believe it has underperformed during the pandemic. On Saturday it was reported that it would be merged with NHS Test and Trace to form the National Institute for Health Protection, responsible for laboratory testing and contact tracing, while other public health functions would be passed to local authorities.

In Ballycastle, a seaside town on the Antrim coast, the beach has been busy throughout the summer, with customers queueing for ice creams and playgrounds full, with little sign of social distancing. The National Trust has restricted entry to the Giants Causeway visitor centre, and the Carrick-a-Rede rope bridge is shut, but some Game of Thrones tours are taking place.