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  • Writer's pictureRichard Cree

Immunity

Updated: Jun 28, 2020

Saturday 28th June 2020

Figures for 27th June

UK COVID Deaths 149 / Total 43,230

James Cook Hospital – Total COVID deaths – 254

All COVID cases within South Tees Hospitals Trust – 8

James Cook Critical Care COVID cases – 3 (3 ventilated)

James Cook Critical Care non-COVID cases – 41

We have admitted another COVID patient to the ICU. The patient has been admitted with traumatic injuries following a fall and is coincidentally COVID positive, rather than the virus being the reason for their admission. Otherwise, the total number of COVID patients in the Trust has fallen slightly in the last 24 hours.

Nicky and I have both had the results of our antibody tests yesterday. The antibody tests are offered to all healthcare workers at our hospital. They detect the presence of antibodies in your blood confirming that you have been infected with the virus in the past. The antibodies are produced in the body by white blood cells called B-Cells. Whether the presence of such antibodies provides immunity and if so, for how long, is extremely contentious.

Nicky and I have both tested negative. This means we haven’t had the virus, right? Well, maybe, or maybe not…

A negative test could indeed imply that you have not been exposed to the coronavirus and have not been infected. It could however, imply that you have only been infected recently and haven’t had time to produce antibodies. It’s believed it can take 1-3 weeks after an infection to produce antibodies. Some people make take even longer and some people might not ever produce antibodies despite being infected.

I know a few people who became ill, tested positive for the coronavirus at that time but subsequently did not test positive for antibodies. Studies have shown that anywhere between 10 to 20 per cent of people who have been infected have little or no detectable antibodies in their blood some weeks later.

It’s starting to look like a mild infection is less likely to produce an antibody response than a severe one. Presumably, the immune system isn’t as strongly stimulated, resulting in the failure to form a significant, lasting antibody response.

Of course, no test is 100% accurate. The home sampling antibody kits sent in the post are particularly unreliable. The two laboratory tests that are available (and used in hospitals) are manufactured by Roche and Abbott. The media have often reported that these tests are 100% accurate but this is not the case. The Roche test detected antibodies in 84% of positive patients, so 16% were missed. The Abbott test missed 6% of positive patients. These rates will increase a little if the sample is taken 20 days or more after the infection. These figures demonstrate the sensitivity of the test; the missed positive results are called ‘false negatives’.

The other measure of accuracy is the specificity of the test. In this situation, this refers to how many of the people who tested positive for antibodies didn’t actually have them in reality (these are called ‘false positives’). Fortunately, in this regard, both tests are nearly 100% accurate meaning that if your test detects antibodies, they are nearly always present.

This is all very well and good but true ‘immunity’ is complex and cannot be measured in this way. We currently do not know whether these antibodies offer full or partial protection against future infections or for how long. Other parts of the immune system cannot be measured by such blood tests. In particular, some white blood cells, called T-cells are an important line of defence. They can trigger infected cells to self-destruct, stopping progression of the virus. They also help the B-cells develop antibodies. Some T-cells can remain after an infection to help protect during any subsequent exposure to the virus. In HIV, one of the reasons the virus is so dangerous is that it destroys T-cells, leading to a failure of your immune system.

In other coronavirus infections, including SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus) and MERS-CoV (Middle Eastern Respiratory Syndrome Coronavirus), T-cells play an important role. It’s likely that the same will be true for this coronavirus. It is difficult to test the body’s T-cell response and so it’s unlikely that there will be a test available to measure this aspect of immunity.


Of course, it’s worth pointing out that there is yet to be any reliable confirmation of anyone contracting the virus twice.

So where does this leave Nicky and I? Both of us believe that PPE offers protection from infected patients. We assumed that the risk of contracting the virus was more likely from working alongside potentially infected members of staff. However, we have to assume that despite working alongside colleagues who became unwell and tested positive for COVID-19 we have not been infected. Or, if we were infected, we were asymptomatic and failed to generate an antibody response. Of course, we may still have some ‘immunity’ if this is the case.

The bottom line is that we resigned ourselves some time ago to becoming infected at work at some point. So this result, whilst not reassuring, does not cause us too much anxiety. We will continue to be careful and cross our fingers. It’s all any of us can do.

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11 Comments


peterburke543
Jun 28, 2020

As always doc very interesting and informative read, but with all the uncertainty regarding antibodies and immunity. I think your last sentence is the one people should take away from this Blog.

All the best keep up the good work.

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Richard Cree
Richard Cree
Jun 28, 2020

@kemag70 Hi – The first case of COVID-19 infection in Italy was recorded on 31st January from two Chinese tourists in Rome. However, the first outbreak amongst Italian citizens was in Lombardy on 21st February. With your negative antibody test, it’s likely that your infection was not COVID-19. Many people in the UK believe that they caught the virus early on in the year but unfortunately, this is probably not the case. Cheers, Richard

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Richard Cree
Richard Cree
Jun 28, 2020

Hi Tom I haven’t seen anything that makes me feel the virus is getting stronger. The virus is rather good at surviving and spreading as it only kills a small percentage of its hosts so technically, it doesn’t ‘need’ to evolve further to survive. We just have to wait and see how long it is before a vaccine is produced and how effective it is. Clearly, the complex nature of ‘immunity’ make designing a vaccine no easy task. Cheers, Richard

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Richard Cree
Richard Cree
Jun 28, 2020

Hi Becky Either of those infections could have been COVID-19 but my money would be on the second one. The first infection was probably a seasonal viral infection, the sort that are very common in March. Secondary separate infections are common after any viral illness. There has not yet been a confirmed case of anyone catching COVID-19 twice or the virus reactivating. Most immunologists predict that those who have had the illness are likely to be protected for at least a year or two (immunity to the SARS-1 coronavirus appears to last at least 2 years and in some people up to 12 years). There is a danger in people thinking they have had the virus already without a positive test…

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Richard Cree
Richard Cree
Jun 28, 2020

Hi Qasim No, we don’t. There’s not really time for us to do that and an awful lot of people claim they haven’t violated lockdown or broken social-distancing rules. Clearly they have all been in direct or indirect contact with someone who is infected though. The virus can remain on surfaces for anywhere from several hours to a few days depending on the material and other factors but nearly all infections are caused by being around an infected person. Cheers, Richard

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