Monday, 19 October 2020

Can you get COVID19 twice? T-Cells to the rescue!

SUMMARY

  • Cases of reinfection with COVID19 have made the headlines creating worry about COVID19 becoming a recurrent disease.
  • A simple COVID19 symptom tracker is shining light on the natural history of the pandemic.
  • They have found re-infection to be rare, even in those hospitalised with COVID19 with no antibody response. 
  • The study was also the first to describe loss of smell and delirium in the elderly as useful diagnostic clues for COVID19 infection.
  • They, and others are showing there is more immunity than antibodies.

Introduction

A recent case of COVID19 made the news in that a young man from the US became infected by two slightly different strains of C19 with the second infection, unusually, being worse than the first. This followed four other reports from Hong Kong, the Netherlands, Belgium and Ecuador - in these cases the second infections were milder. 

Re-infection raises the issue of immunity to COVID19 once again, and the concern that immunity against the virus might be short lived with implications for us all and for the development of vaccines. 

These cases have been widely publicised, creating headlines around the world, but what do they mean in reality? Why am I not too worried about this?

Gathering the data

This week I read results of the Covid Symptom Study App, a symptom reporter designed and developed by Kings College and a health science company called Zoe. It has been led by Tim Spector, Prof of genetic epidemiology and someone who has been studying and making news about the poor health of the UK population for some time. I only wish he was Secretary of State for Health, but has clearly been too busy for party politics.

Today the survey suggests that there are 33,000 people with a new infection as compared to the 17,000 positive tests registered on the Government dashboard. Another big hint why Test and Trace has failed - half of people with symptoms are not even getting tested, never mind traced!

Compared to the publicity about the NHS Apps and their many glitches, this App seems to have been rolled out without much fuss; and, despite some initial difficulties with our creaking centralised administration, is now partially funded by Government.

4 million people have signed up to the App and so it has become a sort of National Register of what happens to people with COVID19. It's experience, and results so far are invaluable.

Learning more about COVID

Soon after its launch, it was the first to identify the loss of the sense of smell as 90% predictive of a positive Covid test. I clearly remember the dithering of the chief medical officer about this useful symptoms which is now recognised as very significant sign of COVID19 infection. The slow pick up of this marker was itself is a symptom of lack of momentum within PHE. 

It is also defining the symptoms which might predict the development of "Long Covid", where symptoms last three months or more and is thought to affect between 20,000 to 60,000 people in the UK. The ability to predict who will develop these protracted symptoms would be invaluable, perhaps, they suggest, to guide early treatment with steroids. (Vitamin D too, I would suggest!) So far it seems to affect more women than men, those overweight, those with asthma, and many who did not need hospital care. 

They also have defined that in older people delirium is a common feature of infection. Like with the lack of smell, this has not yet become recognised officially and it will not get you a tested according to our Test and Trace algorithms, highlighting another reason for our poor performance. 

So how common are re-infections?

Encouragingly, results tentatively suggest that we might not see a return to last winters chaos. For one thing, the results suggest that more people may have been infected than antibody studies suggest. 

Only half of people with COVID19 severe enough to end up in hospital develop antibodies and for them you would expect reinfection to occur, and this doesn't seem to be the case. T-Cells must be coming to the rescue and suggest longer term immunity for those infected with COVID19. This is good news.

The delayed increase in London as compared to the North, also suggests that there is immunity around, and this lack of reinfection should reduce the size of the second wave. 

The UK Twin Registry, another project at Kings, shows that 12% of this random group have antibodies to COVID19 and therefore Tim guesses that a quarter of twins in the Registry have been exposed to the virus; he suggests that it could be double that in care workers. All this is slowly moving us to some sort of herd immunity as well as suggesting a reduced impact on the health and care sectors where initial infections were, and subsequent immunity is likely to be more common.

Reassurance

This epidemiological approach is backed up by some good lab-based science too, with a  recent study adding to a wealth of data that T cells provide immunity and prevent reinfection.

That is why Im not too worried about re-infection. Coupled with, of course, the fact that 40 million people are known to have been infected with COVID19 and reports of reinfection are, so far, vanishingly rare.


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