One of the things people seem most interested in with regard to Covid-19 is antibody testing.
People who've had the virus want to know if they're immune or not. And lots who haven't had it harbour a secret hope they've actually had it without knowing.
In view of asymptomatic spread, many of us would like to know the true incidence of Covid-19. Are we anywhere close to herd immunity?
But antibody testing may not give us the answers we hope to find. I was diagnosed with Covid-19 on March 17. Three months later, on June 17, I had a Covid-19 antibody test with Safetest - a private company run by doctors and dentists. They use a venous blood test sent to a lab, rather than a finger prick, which I'd been advised was far less accurate. Safetest states their tests' sensitivity (rate of false negatives) is 100pc. Testing is done in the accredited private Honeyman lab in Dublin.
I decided to get all six members of my family tested as despite only my daughter and I being sick, we had all lived together in close proximity throughout our illness so there was a definite chance the others had caught it from us but not displayed symptoms.
The results came back after two days - none of the six of us had antibodies.
It was a bit of a blow. Even though the World Health Organisation has said infection does not guarantee immunity, we still know that high levels of circulating antibodies coincide with recovery in hospital-based Covid patients. So it's certainly thought that our antibodies are partly what fights it off, and, if we have them afterwards, it may be we're less susceptible to reinfection. Most vaccine development is based on this premise. The HSE currently advises healthcare workers here that they're immune for three months post-infection.
The company ran the tests twice as they knew I was a confirmed case, but the second test was also negative for all of us. They told me I was the first confirmed Covid patient their test had not detected antibodies in.
Because these were not the expected results, I decided to double-check in case the test was the issue - not the lack of antibodies. This time just myself and my daughter were tested at my local GP and the blood was sent to the National Virus Reference Lab (NVRL) where they use the Abbot Test, which Public Heath England has reported to have a sensitivity of 93.4pc.
Again the results came back after two days. Ella's came back as negative and mine came back as 'high negative', which means mine could possibly be positive on closer inspection. At the time of writing, my blood is being tested for a fourth time.
But let's just say I'm antibody negative - as three tests so far have said I am. What does that mean? The truth is, we don't know.
It may mean I never made antibodies. A recent essay in The Lancet suggested that about 10pc of people may not produce them. It may mean that I had antibodies back in March but I've lost them since. A paper in Nature recently found that most people tested positive for antibodies early on post-Covid, but that 13pc of symptomatic patients had none detectable a few weeks later. Or it may possibly mean even the accredited tests currently aren't sensitive enough to pick up very low levels of antibodies in post-Covid patients.
The bigger question is what does it imply for immunity? Dr Cillian de Gascun, virologist and director of the NVRL, says: "It's likely people are protected for a period of time, even if we don't detect antibodies. Whether that is because of cellular immunity (different to antibodies) or very low levels of antibodies, we don't know."
Prof Luke O'Neill, professor of biochemistry in the School of Biochemistry and Immunology at Trinity College Dublin, agrees.
He says: "It looks like it's about the severity of the infection. People who survive a severe infection will have mounted a strong immune response and will have lots of antibodies and T cells and will be protected completely from reinfection - or if reinfected, will have a mild disease. Those with a milder course first time round will get reinfected but will probably have low levels of Abs and T-cells and will have a milder disease, too. However, we don't know enough yet about the T-cell response. That might be more important than antibodies. So it's possible that those without antibodies have lots of T-cells and may still be protected - hence we have to say we just don't know."
What we do know is this. It's likely we have immunity post infection for a period - but we can't say how long. We don't know if having antibodies is fully protective. But we also don't know if having none means you have no immunity. Time is what's needed here to allow research to work all that out. We can also say antibody testing will not pick up all cases of Covid retrospectively.
Most GPs I spoke to about antibody testing knew very little about it and none I knew had done any. I asked on social media and a myriad of routes to testing were sent to me. It seems an area where private providers - some I couldn't find verifiable accreditation for - are circumnavigating normal doctor-patient channels and interfacing directly with the public, which is both questionable and interesting.
The tests I had were accredited but despite me having had Covid they came back negative. Between the low sensitivity of viral nasal swabs and the limitations of antibody testing, accurate assessment of the true incidence of Covid and of herd immunity is still a long way off. As to my own immunity? Antibody testing left me with as many questions as answers.
Antibody screening with Safetest costs €125. Antibody screening using the Abbott Test is available from TMB and costs €80