Why are people still dying and what if I can’t use the tracing app?

Q How can people still be dying if everyone’s been in lockdown for so long? Will it really be safe to let us all out?

A I know it’s a worry that the ‘stay at home’ rules might be eased when hundreds of people are still dying, but it’s important to understand how public health officials have come to this decision.

It relates to how fast the virus is spreading.

Shortly before the lockdown, Chief Medical Officer Chris Whitty suggested that, although diagnosed Covid-19 numbers were at about 1,500, there could be tens of thousands more – many with mild or no symptoms.

When we were all freely going about our daily lives, it was estimated that on average one person with the virus was infecting three others every three days.

Each of these newly infected people would then infect three others themselves, and so on.

The number of others each person infects, on average, is used to calculate what we call the transmission rate, or R value.

When we have an R 3 – as could have been the case judging by how quickly numbers of cases in the UK and other countries shot up – you see what’s called exponential growth of infection, with the total number of cases doubling or tripling every three days.

It takes roughly five days for symptoms to appear, and deaths occur on average 25 days after infection.

This is why the peak of deaths – and new diagnoses – happened about three weeks after the start of the lockdown, and then began to decline.

With people not mixing, the transmission chains are broken.

Six weeks in, scientists now think the R value has dropped below 1, meaning that not every person with the virus is passing it on.

This means new case numbers will keep going down – and our risk of coming into contact with the virus reduces.

If you can keep transmission rates as low as this, eventually you could see Covid-19 dying out. Hundreds of people are still dying because of that 25-day time lapse after infection. But new infections are falling, and so deaths will keep falling.

How can we keep transmission rates low and make it safer to go out? Through a combination of continued social distancing, hand-washing, and maskwearing – so asymptomatic carriers of the virus are less likely to spread it unknowingly – and isolating, testing, and contact-tracing anyone with symptoms will be key.

Q I’ve heard that the R number – the rate of transmission – has increased over the past few days. Is that true and what does it mean?

A The rate of transmission will waiver. It is likely to be higher in some places such as hospitals or some cities, and lower in others.

It is not only influenced by the natural properties of the virus but also the measures we take and the immunity we have.

It remains between 0.6 and 0.9 in the UK currently, but that will be an average. The risk of getting coronavirus in some places, such as hospitals or very busy, crowded places, will be higher.

Ultimately, the best of way to keep transmission rates very low would be a vaccination: the virus simply couldn’t be transferred to vaccinated people, stopping it in its tracks.

Until then we have to rely on the crude interventions of isolation and social distancing.

Q The Government will make us all download a tracing app to stop the spread of Covid-19, but I don’t have access to the internet, let alone a smartphone.

What will the options be for people like me?

A The app will be optional so no one will be made to download it. And it’ll be only one aspect of the ‘test, track and trace’ system which is being set up. Much of the legwork, including tracking down people who’ve been in close contact with a newly diagnosed patient, will be done by old-fashioned phone call.

This is a well-established system we use in public health to monitor any disease outbreak. For example if you get food poisoning in a restaurant, public-health teams track back to find other customers to monitor for outbreaks.

It is a sensible approach: the countries that have avoided huge numbers and death tolls have used such systems from the first few cases.