Ben Lowry: Lockdowns do seem to work in stopping coronavirus, but the statistics on its spread are confusing

This is due to reasons including dishonesty in some nations and lack of testing in others.

But there is already data to suggest that lockdown, while it creates its own massive problems, is a highly effective short term way to stop rapid spread.

China indicates that lockdown is a success but only if we can trust their figures of 81,000 cases and 3,300 deaths. If at all accurate, it is remarkable – a total of 81,000 equates to one person in 17,000 of China’s 1.4 billion population (0.006%).

One way to interpret the array of Covid-19 statistics is to multiply official figures for infections by at least 10.

Even countries that test widely might only detect a fraction of cases, such as people who had no symptoms.

If you multiply China cases x10 you get near to a million infections, which is less than a tenth of one per cent of people.

That is a miniscule total given predictions that most of the world will get infected, which in China would mean 700+ million cases. If lockdowns have kept it to a million, they have worked.

Or is China just lying on a huge scale? It is the most repressive of the world’s richest countries, and it cruelly pursued whistleblowers in Wuhan.

There are two problems with the lying explanation.

The first is: why then did it give accurate data at first? Perhaps it decided after a certain point to lie to prevent panic. But if so, why has the World Health Organisation (WHO) not even hinted at concerns? It might be that China has lied on an industrial scale and WHO has just missed it, in which case it too will face big questions after this crisis.

The second problem with the theory of lying is why are we not hearing of horrifying death levels? If, say, 10% of China had coronavirus (well bellow a worst case scenario) that is 140 million people. A million or so would be dead.

You would expect that to seep out. Wuhan showed that people tend not to fear police seizing their video phone if they or a loved one are dying. And even China cannot monitor emails of a billion people (millions of whom are western expats, who would be sending home desperate messages).

It seems more likely that while the real number of cases in China might be a million plus, lockdown has nonetheless worked. Even if so, China faces disaster if lockdown ends and a handful of infected people trigger a new outbreak.

One country that is widely believed to be lying is Iran. As of yesterday it had 25,000 cases, 2,000 deaths. Reports as far back as early March of overwhelmed hospitals and mass graves suggest it had penetrated Iran’s 80 million population to a larger extent even then than statistics show for now.

Another method to assess the scale of the virus is to work backwards from number of deaths. If coronavirus does have a 1% fatality rate, then multiply the number of deaths by 100 and you get to a minimum infection figure.

Iran would have 200,000+ cases (probably far more because their death toll is implausibly low). Italy, with 6,800 dead would have 700,000 cases.

But even in western countries that have accurate death tolls it is probably best to multiply by an even higher multiple than 100 in order to estimate case levels, due to a time lag before deaths (at least a week) and the fact that even honest recording systems can miss the real reason for some deaths.

Last week the former Health Secretary Jeremy Hunt suggested 1,000 cases for each death and the UK chief scientific advisor Patrick Vallance called that “a reasonable ballpark”.

If so, then the UK with 422 deaths has almost 500,000 infections, Northern Ireland with 5 deaths has 5,000 and the Republic with 7 has 7,000.

This is far more plausible than the UK’s supposed 8,000 cases or NI’s 172. It explains why many of us now know people who are infected (which would not be so if the UK’s official statistic of 1 case per 8,000 people figure was true).

The low UK stat is in part due to the fact it is testing far less than, say, Germany, and helps explain the far higher German ratio of cases to deaths (33,000 to 160). Yet even Germany, on a x1,000 ratio, has far more cases than it has yet found.

On the same ratio, Italy would have millions of cases (but the x1,000 ratio becomes less applicable as the disease advances).

If we apply the x1,000 ratio to the world, it is approaching 20 million cases, still far short of worst case scenarios of majority infections (ie billions).

If this is all evidence that lockdown works, then it is not hard to see why it works. Statisticians have pointed out that in a normal flu every person infects 1.3 people, which is 14 people at 10 steps (1 x 1.3 x 1.3 etc). Coronavirus every person infects 3 people, which is a breathtaking 60,000 infections at 10 steps (1 x 3 x3 etc)

Italy has just had its third day of slightly lower death tolls than Saturday. That could suggest the increase there is no longer exponential.

Even if lockdowns work, there is a better way: South Korea had no lockdown but tested and traced ruthlessly and has low infection rates and deaths.

None of these approaches help with immunity. Even if Covid-19 spread is stopped fully (which is a long way off) there is no herd immunity. The non infected are vulnerable to new outbreaks until a vaccine, maybe not before 2021.

Last night yet another theory was emerging: that far more people than thought are already infected in the UK and abroad, maybe half the population, but with a far lower percentage of the infected suffering badly than expected.

• Ben Lowry (@BenLowry2) is News Letter deputy editor