UK strain: use of incorrect figures is more infectious

Passengers at Melbourne Airport’s Terminal 4, where a cafe worker tested positive. Photograph: Che Chorley

Let’s get some numbers straight. The UK strain is not 70 per cent more infectious, as we were originally told. It’s not even 50 per cent more infectious, the latest widely quoted figure.

According to the most authoritative source of data on the detailed epidemiology of transmission risk, the UK government executive agency Public Health England, a person who is infected with the UK strain of coronavirus will pass the virus on to 14.7 per cent of their close contacts.

Say somebody infected with the UK strain had 10 close contacts. On Public Health England’s numbers, eight of those contacts would not be infected.

To be clear, the UK strain is more infectious. Somebody infected with the original Wuhan strain is likely to pass the virus to 11 per cent of their close contacts, according to Public Health England. That means the UK strain is roughly 34 per cent more infectious than the original strain.
But in the context of very small case numbers, there is no reason to believe that the, so far, very limited spread of the UK strain in Melbourne cannot be contained with widespread testing, rigorous contact tracing and some limited suppression strategies such as those introduced in a proportionate way in NSW.

Catherine Bennett is an epidemiologist with a public health background in real-world disease outbreak management. She’s not prone to hyperbole, unlike Victorian Premier Dan Andrews, who struck fear into the hearts of Victorians when he told them the UK variant is coming at them with maximum velocity. “If you say the UK strain is 40 per cent more infectious, it sounds very dramatic, but most people don’t pass it on, as we’ve seen in Brisbane and in Perth,” says Professor Bennett.

“From what was presented today, I was really worried we were going to get more news about wastewater positives or something else that would have made me feel nervous as an epidemiologist. But then I realised we were talking about the same cases we already knew about, only four outside of the hotel, all of them direct contacts, two of them spouses.”

Despite Mr Andrews saying contact tracers can’t keep up with how quickly the UK variant is spreading, there is no evidence the UK strain has a shorter incubation period. It doesn’t have a different transmission route profile.

Professor Catherine Bennett, Chair in Epidemiology at the Faculty of Health at Deakin University.

“We shouldn’t take from what we know about these cases that the interval between one case and their contacts becoming infected is too short for us to use our normal, aggressive contact-tracing methods,” Professor Bennett says.

“It is a concerning situation, but I don’t think people need to be told this is worse than anything else, as if the world hasn’t seen this yet. That’s not evident in what we’ve been presented, and it just causes more fear.”

In many of the countries where the UK strain has now spread, epidemic curves are falling, not exponentially rising. Granted, some of those countries are in lockdown, but if the UK strain was spreading with unprecedented velocity, you would expect to see exponential rises in case numbers in the countries where the strain has spread.

NSW has proven that public health measures with limited suppression measures such as reducing the number of guests allowed to your home is a successful strategy for containing outbreaks, and those principles apply equally to the UK strain.

“With a low base of cases, you can still keep it under control, whether it’s a new variant or not,” Professor Bennett says. “When people say to me ‘what do you think of this decision on lockdown’, I say ‘well look at the evidence’.

“And on what was presented on Friday, putting an entire state into lockdown for five days didn’t appear proportionate having just four cases in households.

“We could have put suppression in place to help prevent super-spreader events without closing down every business and putting the state into a full lockdown.”