Every country seeking to ease lockdown measures now must negotiate an ‘extremely difficult balancing act’ to keep the pandemic under control, Professor Chris Whitty said. PEOPLE: Mother thanks Sheffield NHS staff for saving son's life after he collapsed on a football pitch In particular, the virus reproduction ‘R’ number must be kept below one - meaning each infected person could expect to pass it to fewer than one other person. Prof Whitty said: “We need to make sure that R does not go back above one. Because if not we will go back to a second wave. “It is entirely plausible for a second wave to actually be more severe than the first if it is not mitigated. “Every country has got an extremely difficult balancing act, and we all need to be honest about the fact there are no easy solutions here. “Covid-19 is a very long way from finished and eradication is technically impossible for this disease.” BUSINESS: Sheffield brewer speaks out on how pubs could operate in the city after lockdown Outlining several key unknowns, Prof Whitty said: “It may be that there's a seasonal element and if so, for most respiratory viruses, they are more likely to be transmitted, there is a higher likelihood of transmission, in the winter. “The winter is always worse than summer, spring and autumn for health services, and we need to think about this in terms of how we come out for the next phase.” He said social distancing measures are likely to reduce rates of flu and other respiratory illnesses when winter arrives.