Testing travellers a week after their arrival in the UK could catch 94% of coronavirus cases and halve quarantine times, scientific modelling has suggested, as ministers consider proposals to reduce the 14-day self-isolation for those coming from high-risk countries. Boris Johnson said on Tuesday that Europe was beginning to experience a second wave of Covid-19 infections, increasing the pressure to find measures to prevent the spread of cases to the UK. The UK government advised against all non-essential travel to Spain on Saturday and, with just a few hours’ warning, imposed a 14-day quarantine for those arriving from the country, plunging holidaymakers and the tourism industry into disarray. “Let’s be absolutely clear about what’s happening in Europe: among some of our European friends, I’m afraid, you are starting to see in some places the signs of a second wave of the pandemic,” Jo said. There has been a sharp increase in cases in Spain, as well as concern over rises in France, Germany and Belgium. “It’s vital that when people are coming back from abroad, if they are coming back from a place where I’m afraid there is another outbreak, they must go into quarantine.” He confirmed that the government was examining ways in which the impact of the quarantine could be mitigated and would try to make sure that the science was “working to help travellers and holidaymakers”. Scientists have cautioned that mass testing at airports is unlikely to prevent the need for quarantine measures as it may not pick up infections caught during the flight, although it could help cut the time travellers need to isolate. Outbreak modelling, which was published by the London School of Hygiene and Tropical Medicine (LSHTM), shows that quarantining people for eight days on arrival from the EU and testing them on day seven, with a 24-hour turnaround in test results, could reduce the number of infectious people re-entering the community by 94%, compared with no quarantine or testing. All approaches under which travellers were quarantined for at least five days, the typical incubation period for the virus, and released subject to a negative test were “highly effective”, the models show. For example, testing people on day five of quarantine and releasing them on day six if the results were negative cut the potential for transmission by 88%. On Monday, Dr Sam Clifford, a postdoctoral fellow in machine (statistical) learning, and Billy Quilty, a research assistant at the Centre for the Mathematical Modelling of Infectious Diseases at LSHTM, said swab tests could be an effective tool, but not if used in isolation. “We understand the need for people returning to be able to get back to their families and jobs; combining PCR [testing] with a week of quarantine could prevent up to 94% of infectious persons entering, and could help people get back a week earlier than under the current two-week quarantine policy,” they said. “Testing immediately on arrival is likely to prevent about only 50% of infectious persons entering the community. By seven days, a majority of people who will ever show symptoms will have noticed their symptoms and will self-isolate or seek medical attention. “Also by that time, PCR testing should detect most of those infections with a long incubation period or … asymptomatic infections.” Ministers are considering whether tests on arrival at airports, combined with follow-up “spaced tests”, may cut quarantine time. “If you test once, you pick up only a small percentage – it’s not useless but it’s not far off,” a government source said. “If we space-test we pick up a much bigger proportion. That’s the crucial issue in this.” Ian Jones, a professor of virology at Reading University, said quarantine could potentially be shortened by giving people tests every other day while they self-isolated, and releasing them from quarantine when they tested negative three times in a row. He said testing on arrival could help find asymptomatic cases, and if a test on arrival was considered day one, travellers could be tested on days three and five, reducing the quarantine period to one week. “My own view is that the UK government has become a bit doctrinal on this, but if we have to have it, it could be realistically shortened if it was combined with regular tests, say, every other day,” he said. On Tuesday, Scotland’s first minister, Nicola Sturgeon, said she would not book a foreign holiday herself and that while her government was looking at potential testing alternatives to quarantine, people should remain cautious about foreign travel. She said there was a risk that giving up on 14-day quarantine could lead to “more cases slipping through the net” if the virus was not yet detectable. “Certainly, testing people on arrival and then saying, if you’re negative you don’t have to quarantine, that would be a big risk,” she said. The Spanish government’s spokeswoman, María Jesús Montero, said the administration of Pedro Sánchez’ has not abandoned its efforts to get the UK to rethink its travel advice. “The government is using all the available mechanisms to get this situation reversed, and reversed as quickly as possible,” said Montero, who is also finance minister. “You can rest assured that the prime minister himself and all the relevant ministers are keeping up their contacts so that people can understand the reality in our country.” The health minister, Salvador Illa, rejected suggestions that Spain was in the middle of a second wave of infections. “There are outbreaks that are being detected early – and 70% of them involve fewer than 10 cases,” said Illa. “The situation is a bit more worrying in Catalonia and Aragón but measures such as social distancing, which is being practised by the overwhelming majority of people, will allow us to control them and cut off transmission in those areas over the coming days and weeks. “That’s why, in my opinion, we can’t talk about a second wave of cases. There are outbreaks in areas where transmission is very high, but the measures in place will help us bring them under control in the coming weeks.”