SMALL THREAD: I have seen concerns going round about the theoretical possibility that vaccine mRNA could end up altering our own genomes, and that could cause long term consequences. I will start by saying that this is not a material concern, and will try and explain why. 1/n https://twitter.com/ArisKatzourakis/status/1335031212335828992

I think some of these concerns stem from the rather confusing terminology 'genetic vaccines' that has been used to describe mRNA vaccines, but also some incorrect statement that have been made, and also, of course, the fact that there is an antivax movement 2/n

RNA is indeed a type of genetic material. Our genomes are made up of DNA. DNA makes RNA which is translated into proteins. This is called the central dogma of molecular biology. Now there is some debate around whether this is indeed a dogma, and what exactly the dogma is 3/n

The term is credited to Crick, who co-discovered DNA, and it has been said that when he coined the term, he didn't really know what dogma meant and that he did not intend it as such. Also perhaps the dogma has been slightly misrepresented 4/n

The point is that information from the genome, to make proteins, flows in one direction. mRNA vaccines basically skip the first step, and interact with our cellular machinery to make the proteins that train our immune systems 5/n

As with every rule in biology, there are exceptions. Retroviruses which have RNA genomes, can subvert this central dogma and insert themselves into their host genomes in DNA form. Very, very occasionally, other viruses can recombine with retroviruses or retroelements 6/n

And end up integrated into the host genome. The leads to genomic 'viral fossils', which form the basis of paleovirology, the field that I work on. However, between integration and the formation of these fossils, are several incredibly rare steps that are required. 7/n

This is why the process is so rare. These endogenous viruses appear in their host genomes on timescales in the millions or tens of millions of years. You need the integration to be harmless, to happen in a reproductive cell, and for it to be passed on and spread 8/n

Even if genomic integration were to occur, which is exceedingly rare, the outcome, if it were harmful, would be that the immune system would mop up the cell with the integration. And integration is even rarer for acute viral infections like coronaviruses, or flu. 9/n

In fact, there are absolutely no known viral fossils from coronaviruses, in any species at all. Despite the fact that we have thousands of genomes to look through for them. It just hasn't happened over the evolutionary history of our ancestors, ever. It won't happen now 10/n

Viral infections make mRNA. And they do so, far more efficiently and effectively over a more sustained period of time than vaccine mRNA, which simply transiently persist in the cytoplasm, in other words not near the genome, makes protein, and is cleared up 11/n

So the chance of vaccine mRNA ending up in the genome is negligible. And its even lower than the chance of a viral integration happening as the result of a natural infection. In fact, one might argue, that if integration of coronaviral mRNA is something that concerns you 12/n

The best way to avoid it is to get the vaccine, which will fight of the natural infection which would be more likely (but again, vanishingly unlikely) to ingegrate into your DNA. But neither is going to happen, and should not concern us. Trials are done, the vaccine is safe. 13/n