Over the last few days we’ve seen a big rise in the number of positive Covid-19 tests every day.
The seven-day average is well above 2,000, compared with fewer than 550 in early July.
Yet the number of Covid-19 deaths has remained relatively low.
This isn’t because the figures are being fiddled to scare us or to hide the truth.
Nor is it because the virus has become less dangerous over time.
But there are big differences between the situation now and during the lockdown in March, April and May.
First, tests are much more readily available, which means that people who test positive are more likely to have mild disease or no symptoms.
Back in April when there were more than 5,000 positive cases per day, you could only get tested in a hospital or a care home – so you were already high risk if you tested positive.
Second, the age distribution of people getting infected is very different from the Spring.
The chance that Covid makes you really sick increases hugely with age – the risk of death once you get infected doubles for every six to seven years of age, which means it’s multiplied by eight for every 20 years older.
Back in March and April the decision to send people from hospital back to care homes led to many of the oldest and most vulnerable people being infected.
Now, the group most likely to test positive is adults aged 20 to 29, who are unlikely to get severely ill and die.
The problem is that unless we control the virus in younger people, infections and deaths will rise in older people.
Third, we are better at treating people who get seriously ill with Covid-19 than at the start of the pandemic.
We know that corticosteroids reduce mortality in the sickest patients, and intensive care doctors are probably better at managing the condition more generally.
Fourth, it’s vital to remember that the number of hospitalisations and then the number of deaths only rise some weeks after the number of cases goes up.
For example, in Marseille in South France the number of cases went up a while ago, and intensive care is now filling up.
We need to get on top of things before that happens in the UK.