It is inevitable cases will go up when restrictions have eased. It is like putting a chicken infected with salmonella in the freezer, it doesn't kill the salmonella, it just stops it multiplying (hence why you are advised not to refreeze thawed meat). Same with lockdowns, they slow or stop the spread of the virus, but the virus is still there, in a kind of dormant state, until restrictions are eased, people start mingling, and off it goes again. The only way to control it properly is vaccination, like the only way to get rid of salmonella on your chicken is to cook it thoroughly, not keep putting in and out of the freezer. What the periodic lockdowns do is to keep the mean infection rate at a level which the NHS can cope with, whilst at the same time trying to avoid completely taking peoples lives away. Until a large enough number of the population is vaccinated, we will continue with this cycle of infection rate going up and down, and going in and out of lockdown. The only alternative is a permanent Spring-type lockdown but that would be catastrophic economically and for mental health.