An antibody test that shows that you have Covid-19 infection will be launched to the NHS and treatment staff starting next week. So what happens when you are stated positive? Continue as before – and I must know.
Part of the work of a medical correspondent is being involved. That means volunteering for medical trials, tests, and so on. I forget how many times I rolled up my sleeves to give blood to illustrate stories, or went to an MRI scanner to imagine my brain. That’s what we call “show and say” in the TV trade. So when the home antibody test was first on the news I set out to show how they work.
All tests are a little different in how you do it. What you need is a drop or two of blood, which you put in a hole, add a little chemical and then in a few minutes you get the results.
Positive results come, as do pregnancy tests, if you get two lines in the sample window. I did a finger prick test on the camera and was surprised, and delighted, found that I was positive for antibodies. Since then I have done further reports on antibody testing and have had the same positive result every time. You can see photos – blood reasons – of three positive results, even though one of them has a faint line.
Imperial College London is testing this home antibody test for accuracy and ease of use. One team there calculated that my repeated positive tests made it “very likely” that I was continually producing wrong results. In other words, it seems like I definitely have a coronavirus.
Fergus at Covid
As a BBC medical correspondent, since 2004 I have reported the threat of global diseases such as bird flu, swine flu, Sars and Mers – both coronaviruses – and Ebola. You could say I have been waiting for most of my career for a global pandemic. But when Covid-19 came, the world was not ready as it should be. Now here I hope, like everyone else, it will go away. Sadly, we may have to live with coronavirus without limits. In this column I will reflect on the new reality.
So when is this? I have had no symptoms in the last few months. I rarely get sick, but I suffered from pneumonia in early January. I was sick for about 10 days and suffered a cough and high temperature. I can’t let go. My general practitioner in Windsor diagnosed a bacterial infection and gave me antibiotics. This helps a little, but at the end of January I need another antibiotic. This seems to have done the trick. Is that really Covid-19?
I think not. The first confirmed coronavirus case in Britain was in late January when two people from China fell ill in York. It wasn’t until a month later that the first case of domestic transmission occurred. Note that although I have reported an outbreak in China in mid-January, the furthest field I have visited in the last few months is Christmas in Brussels.
So I don’t think I’m missing the story here – the first case of corona virus in the UK is not me. But after that I had no symptoms at all. No cough, not high temperature, normal odor and taste, and no aches and pains, headaches, diarrhea, conjunctivitis, skin rashes or other warning signs that may be registered by the World Health Organization.
So when I prick my finger, I have no hope that I will get positive results. I’m impressed honest. The test that I did showed positive for IgG antibodies – this is what forms at least two weeks AFTER infection.
I can tell you that having a positive test doesn’t change my mindset.
I still, when I walk around, assume that everyone I meet has a coronavirus, and I have it. I don’t want to infect anyone, and I don’t want them to infect me.
I am still an obsessive handwashing – having told the British public repeatedly about the importance of maintaining distance and social cleanliness, I feel I need to set an example. Every public toilet I went to involved a demonstration of what I hoped to wash my hands perfectly. I actually didn’t sing the happy birthday song twice loudly, but I hummed in my head.
At the beginning of the coronavirus epidemic in the UK, there was a lot of discussion about how antibody tests could finally help us get out of the lock. In March the government spoke confidently about antibody tests as a game modifier, because they would help show who was previously infected with Covid-19 and therefore protected.
Unfortunately it’s not that simple.
The government bought 3.5 million finger-prick antibody tests, but when they were evaluated by scientists at Oxford, they said none of them were tested accurately enough.
Many things have changed since then. Now there are several laboratory-based antibody tests that seem to be quite reliable.
British Public Health has evaluated antibody tests from Roche and Abbott. Both of them need blood drawn, so it’s not a test at home. Samples must be sent to a laboratory for analysis.
Now you can also buy home antibody tests that you must send to the laboratory. This is quite accurate, but you don’t get instant results.
The accuracy of the test is based on the specificity and sensitivity.
With coronavirus, you want to make sure the antibody test is very specific so you don’t get false positives. This can be dangerous, because it means some people are told they have antibodies when they don’t. They may be lulled into a false sense of security, taking fewer precautions to guard against infection.
Both Roche and Abbott’s tests are very specific, with almost 100% accuracy. This is very convincing. Then we come to sensitivity. This is a possibility the test gives false negatives. The PHE evaluation showed the Roche test to be 87% sensitive with samples taken 21 days after symptom onset while the Abbott test was 93%. This means that some people who definitely have antibodies to coronavirus might get “false negative” results. This is less important, but it’s still a mistake.
The two companies said they could give 10 million tests to Britain and the government said Antibody tests will be launched to frontline health workers starting next week.
But for what purpose? If you have the Roche or Abbott test and get positive results, you can be very sure that you have Covid-19. This will be very useful for anyone who does not have a nose and back swab test. Remember that for current infections, do you have Covid-19 now. An antibody test tells you about past infections. In addition, you need to wait several weeks for the antibodies to appear on the test.
So that is good. A reliable positive antibody test means you are free from locking, free to meet with friends knowing you are not contagious and unlikely to spread disease, right?
Not fast. It’s not that simple.
There is no consensus on what a positive antibody test means for an individual. Some virologists I met thought that it would give you a level of protection from coronavirus, and especially from severe symptoms, but whether it would last for months or years is uncertain.
With Sars, antibody levels begin to disappear after two or three years.
There are other complications. Current antibody tests do not distinguish between the presence of neutralizing antibodies, which will clear new infections, and non-neutralizing antibodies.
We also don’t know the importance T-cell response – Other parts of the immune system, which do not involve antibodies.
So, having antibodies to coronavirus might not be the locked out way you might expect.
Everyone I spoke to said no one had to change their behavior based on a positive antibody test.
So what’s the point of launching antibody tests for healthcare workers?
First, it will help build a picture of how many people in the UK have coronavirus. Current estimates are faint, and range from around 17% in London to 5% elsewhere in the UK. That’s a very large way of 65% or thereabouts estimated to be needed for herd immunity – IF it turns out that people with antibodies are immune.
This will also give us the first truly accurate picture of how many people have the corona virus without realizing it, which is called a case without symptoms – people, it seems, like me.
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