Tuesday, 28 April 2020

Day 44 of self-isolation - Can you get Covid-19 a second time?

We had our weekly delivery from Waitrose; we wrote down the expiry dates and I sprayed it all - spraying makes the dates illegible in some cases. And we got a Radio Times!

Can you get Covid-19 a second time?

The short answer is, we don't know.

The longer answer is, it depends. With some diseases, the antibodies that you develop in response to the disease, last for many years. With others, much less.

There is also the question of virus mutation. Viruses evolve just like other life-forms (unless you're in a religion that doesn't believe in evolution, in which case what happens is God creates a new virus every so often, but the effect is the same). That's why flu comes round each year. If you had last year's flu, that doesn't give you immunity to this year's. That's why you get a flu shot each year (or, if you're an anti-vaxxer, that's why you carry an onion wherever you go). That's why the common cold recurs - we don't seem to get immunity to it.

Coronavirus is actually a family name "Coronaviridae", sub familiy "Coronavirinae". That family includes SARS, MERS and the common cold. Influenza is part of a different family, Orthomyxoviridae. I know all this because I just Googled it. I'm not a medical doctor.

All of these consist of a single strand of RNA, so if someone tells you that DNA is the code for life, tell them that - although some people wouldn't classify viruses as being alive. Well, it certainly replicates.

The correct name for this is SARS-Cov-2. The disease it causes is Covid-19. "Coronavirus" is a word that is commonly used, but technically it refers to a whole family of viruses.
Both influenza and SARS-Cov-2 are about 100 nanometers in diameter. A nanometer is a billionth of a meter. So, if you put a thousand of these side by side, they'd reach a tenth of a millimeter. Flu is a strand of RNA of about 14,000 nucleotides; SARS-Cov-2 about 30,000.

So, back to the question - can you get Covid-19 a second time. We don't know. The WHO points out that there's no research that says that you get a length of immunity, but there's also no research that says that you don't. Also, if the virus mutates sufficiently, any immunity that you had to the first version, might not work against the second. Indeed, I'd say that it probably won't, because if it did, that second version wouldn't be able to spread. A new version has to evolve resistance to existing antibodies, to be successful.

People talk about "herd immunity". This is the concept that if 60% or 70% of the human "herd" is immune, then the virus would find it very difficult to spread - that's why we try to get a very large percentage of the "herd" vaccinated. Except anti-vaxxers, of course - they can keep an onion in the room and I hope that protects them.

If you can get it a second time, does that mean that vaccines will be useless? Again, it depends. I'd assume that the Oxford University vaccine project has already thought about this, and is aiming to make a vaccine that will also work against variations in the genome.
It's possible to test people for antibodies, and if they have them, that shows that they had the virus, and have beaten it. Maybe you could even give such people a badge to wear "I beat C-19". But are these people immune against a second dose? We don't yet know.

So, in summary. I'm not pessimistic, but neither am I as blindly optimistic as some, that infection confers immunity. And until it's proven that it does, the idea that you can test people for it and give the immunes a badge or certificate, is unproven.

But I can tell you this - follow the guidelines from your government. Wash hands, social distance and wear masks

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