The recent drop in new daily reported Covid cases in the UK has led some scientists to hope that the country has reached the peak of this wave – but others say the dip could be something of a mirage. According to the latest figures from the Office for National Statistics, based on swabs collected from randomly selected households, about 1 in 75 people in the community in England had Covid in the week ending 17 July, up from 1 in 95 the week before. The survey suggests infection levels have also risen in Wales and Northern Ireland, although the trend in Scotland was unclear. However, case data, based on those coming forward for testing – often once they have symptoms – is painting a different picture. On Friday 36,389 new cases of Covid were reported in the UK, down from 39,906 the day before and the sixth day in a row that cases were below the 54,674 figure reported on 17 July. The decline has led some to voice cautious optimism. Tweeting about Thursday’s figures, Prof Eric Topol, director of the Scripps Research Translational Institute in California, wrote: “This could turn out to be the best Covid news of the day,” adding along with the prayer hands emoji that new cases in the UK appeared to be starting a descent. But as so often in this pandemic, it will take time for the situation to become clear. Dr Mike Tildesley of the University of Warwick, a member of the Scientific Pandemic Influenza Group on Modelling (SPI-M), said it was impossible to tell whether the recent fall in cases meant the tide was starting to turn. “We really need to see a trend, and if this continues for the next week,” he said. “Right now it could be a blip.” A key factor is that it will be two to three weeks before the impact of the relaxation of Covid restrictions on 19 July and the influence of school holidays begin to be seen in case figures. Many schools in England only broke up on Friday. While the relaxation of restrictions is expected to boost the spread of Covid, school holidays may lead to reduced transmission – as well as testing. However, with the majority of children not eligible for vaccination, the return to school in September could fuel a further rise in cases. And there are other factors including Euro 2020 – there are signs that mass gatherings for the matches may have fuelled an increase in infections. “Given that the final was on 11 July, the peak – and then dip – around four days after that, does coincide with any such infections being reported in the next four or five days later,” said Prof Rowland Kao, an epidemiologist at the University of Edinburgh who also contributes to Spi-M. “If so, it could be that what we are seeing is a decline that is due to the passing of that possible [event] – and it may be followed by a more sustained rise.” Another factor relates to immunity. While documents released by Spi-M on Friday dated to 14 July noted signs of a slowdown in growth in the north-west of England, something ONS data suggests has since turned into a decline, the group suggested there was no clear indication from observed local antibody prevalence data that herd immunity was causing the downward trend. However, Kao said it is possible that factors with a more sustained impact than the football could be at play in the UK. “In particular, the proportion of individuals with either natural or vaccine-induced immunity is getting high, and if people are being more aware of the need for continued personal measures to control Covid than the modelling anticipated … then together that may be enough to signal a more sustained decline, at least in some areas of the country,” he told the Guardian.