The commercial kits are tempting, but offer little certainty when we aren’t even sure that antibodies confer immunity
“Does anyone know of a private Covid antibody test that is properly reliable?” asked one of my friends on WhatsApp.
The question made me curious. Having antibodies, of course, means you’ve been exposed to the virus and you’re unlikely to spread it. But with false negatives and positives, it’s no guarantee and you’d still want to keep a distance from vulnerable people. Also no one knows how long the immunity lasts.
At the moment, the only tests available to ordinary people are commercial kits on sale over the internet. I had a quick rummage online and it looked like some may now have regulatory approval. But are they really any good? How do they work? How much does it cost? And will I feel impregnable if I get a positive answer?
It goes against the grain to shell out £100 (£160 if you add same-day delivery within the M25) for a private test of uncertain provenance, quality, reliability and significance. But I ordered one to road test it. After a bit of a kerfuffle, a cheerful bike courier (helmet, no mask or gloves, hadn’t had the test himself because “it costs too much for me”) delivered the elegantly boxed kit and waited patiently for me to do it. I may be a doctor but I found it very tricky. I tried to follow the written instructions but if you’re not a natural Ikea assembler, you may struggle as I did. You use a lancet to prick your finger and milk 10 drops of blood into a tube. I’m embarrassed to admit that I filled it from the wrong end – not realising that you had to take the top off first. I couldn’t get enough blood out of my chubby fingertips – even after four attempts. Luckily my GP partner arrived, shoved a needle into a vein in my arm and we filled the tube from the right end. By this time, the puncture sites in my fingertips had started dripping and there was blood all over the place. I felt like an idiot.
The results will be ready in a couple of days but, in the meantime, if I have any Covid questions or feel unwell, I should call NHS 111 according to the kit supplier’s website. This default setting by the private sector always makes me smile wryly. To be fair, the company I used is offering a discount to NHS staff – although I’m not sure that this absolves them of a duty of care to the consumer.
The test claims that it has “demonstrated specificity and sensitivity of greater than 99% 14 days or more after symptoms started”. This means that it is unlikely to give a false positive or negative result. It has been certified for use by the EU and is undergoing validation testing in the UK by public health organisations. It tests for immunoglobulin G, the antibody that rises more slowly after infection but stays around longer in the body – hence the 14-day lag. Kits that include immunoglobulin M, which is the antibody that appears more quickly after infection, are also becoming available.
Authorities including the US Food and Drug Administration are giving emergency use authorisation to get more antibody testing kits on to the market to answer the all important questions: what percentage of the population has been exposed to the virus; does the presence of antibodies confer immunity; and, if so, for how long? And antibody-rich blood from recovered individuals (“convalescent plasma”) can also potentially be used to treat infected patients with life-threatening disease.
So the kits are useful for the study of populations and to identify potential antibody donors. But should you rush out and buy one? The World Health Organization says that the tests can show if you’ve had the virus but that there is “no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection”.
The leading consultant oncologist Prof Karol Sikora argues that the kits are probably reliable but not necessarily useful for individuals. He says the dream ticket would be a test like a piece of litmus paper that you could put in the mouth to reveal both the presence of the active virus and antibodies to get an instant result. Biotech companies are working on it but it’s a huge challenge. As things stand in the UK, there’s no freely available, officially sanctioned antibody test to show previous infection and no wholly satisfactory antigen test to show active infection. (The antigen test relies on a swab being shoved up your throat and nose and transported to a distant lab for analysis. False negative rates are as high as 25% and portable tests are still unreliable.)
Sikora says there are three groups of people on the streets, “the susceptible, the infected and the recovered or so-called immunoprivileged”. We can’t be sure but, based on experience with similar Sars and Mers viruses, he thinks that the recovered group who have antibodies are probably immune. How strong or long-lasting that immunity is, though, is anyone’s guess.
The rate of seroconversion (the percentage of people who have antibodies) in studies is lower than you’d expect given the prevalence of the disease (between 1.5% and 20% in published studies and around 10% in Sikora’s small study). This could be because the body can mount a swift and effective defence against a virus without forming lasting antibodies. So if you test positive for the virus (antigen test) but negative for antibodies, that means that you’ve had the infection. But are you immune? The answer is a weak “maybe”.
Even if you are immune, what about the ethics of granting immunity passports– a kind of get out of jail free card – to those who test positive? The ethicist Prof Ezekiel Emanuel argues that immunity-based licences would be good because they would free up individuals who have been infected already without worsening the situation of those who haven’t. Licences would be based on hard facts so would not be discriminatory. That may be so, but doesn’t allow for the fake or stolen documents that would be inevitable in our ethically impure world.
Where does all this uncertainty leave us? Should my friend shell out £100? Will my life change when I get my result? Sikora says “you can wear your positive (antibody) test as a badge if you want to but you still have to stick to the law”. Perhaps it would give you peace of mind if you can’t resist a cuddle with a grandchild, he concedes, and frontline key workers in hospitals and care homes could feel and be safer. Ongoing population-based antigen and antibody testing are clearly vital tools in planning an exit strategy from lockdown. But personally, I wish I’d saved my money –and fingertips.
This article was first published in The Guardian.