We need broader and more accurate testing, says Grant Schofield.
I’ve been following the recent news with interest, particularly around the numbers of Covid-19 cases in different countries. In New Zealand, as most of you know, we’re in lockdown for four weeks, with a view to eliminate the infections from Covid-19.
To eliminate a virus, which we’ve never done before in this country – we can’t even eliminate measles, which is symptomatic and we have tools to measure it accurately – you need to know whether you’ve got it in the first place. And we need a near perfect measurement technique. It might surprise you that the Gold Standard at the moment for measuring whether you have a Covid-19 infection is what’s called real-time PCR. It’s a genetic test. It’s a swab test in your throat or your nose. Does it miss anyone? This is a crucial thing. Well, actually, this is the problem with the test. For real-time PCR, the sensitivity is about 0.7. It can accurately identify 70% of the cases. It tells 30% of the people who really are sick, that in effect, they’re not sick. And it’s a big deal, isn’t it? Because you’re sending those infected people away, into the community.
That’s one thing. We don’t have a perfect test, so we don’t even know if we’ve eliminated it.
The second thing is, there are potentially a large amount of people walking around out there who are asymptomatic.
A small village in Italy was on their first symptomatic case. They tested the whole 3000 people in the village and a high proportion of the infected cases were asymptomatic. Iceland tested large parts of the population. And what did they find there? About half the people are asymptomatic.
We haven’t been able to test on a broad scale, or with enough people, to tell actually how widespread this is.
Lastly, even if that was all perfect, what we can’t tell at the moment is if you’ve already had Covid-19 and recovered from it. We need serological testing for that, which is by antibodies. What you would need for that to happen is to survey large amounts of the population to see who has had it. We need to have those numbers, at a population level, to be able to calculate the all-important infection fatality rate. What does that mean? It is the number people who have got it, and then the number of people who have died who have got it. That’s what we’ve been concerned about – this potentially deadly virus in the community. Exactly how deadly is it?
We need to know that number to work it out. Now, the initial calculations were in the order of 4 percent. That’s come down markedly in the last few days. It’s looking more like 0.3 percent, according to Oxford Center for Evidence-Based Medicine’s best estimate. At what point do you decide it’s worth the economic harm and the health harm we’re causing from the poverty that follows. We still need to understand that to make our best decision on that. For New Zealand in particular, it is not possible to eliminate a virus with the testing regimes and the accuracy of the tests that we have. We need a Plan B.