For anybody who has heard whispers of problems with vaccines and fertility- I’d like reassure you- see below 1/n

First off bat- vaccines don’t cause infertility. Never been suggested before. It arose in Covid context because someone claimed that the protein that vaccines target ( the spike protein) shared some building blocks or amino acids with a protein involved in placentas... 2/n

.. called syncytin-1. This much is true. It is also however true for just about any protein you care to choose. For a really beautiful but very technical explanation, see here 3/n https://twitter.com/andrew_croxford/status/1334593606196187136

For those not fluent in molecular biology, basically he took the 3 most common proteins and all of them contain the same building block sequences somewhere. If generating an antibody (which is partly how vaccines work) to the spike protein of the covid virus... 4/n

...was going to cause problems, it would not be restricted to syncytin-1 and would cause diverse and catastrophic problems immediately (spoiler- they don’t). The body’s immune system is set up to avoid doing this for obvious reasons. 5/n

Last nail in the coffin of this is that THIS IS THE BODY’S OWN NORMAL RESPONSE to virus. We produce antibodies to the spike protein. A vaccine just cleverly mimics this without giving us the actual disease. If a vaccine caused infertility, so would getting Covid! 6/n

So in summary for this particular piece of speculative nonsense... it is definitively speculative nonsense. However it does lead me to a more general point. It is REALLY hard to prove a negative. This one below is a great example 7/n https://twitter.com/mark_toshner/status/1340229783519703042

I am pretty confident in 3 months we won’t be involved in a mutant alligator vs human war (though post 2020 have to be careful making predictions). But if you ask me to PROVE it. I basically can’t. So anybody can claim a possible long-term complication and I can’t disprove it 8/n

What I can do is reassure you they are very unlikely and getting ill or dying from Covid is not. So far 24 million and counting have been vaccinated. There are ZERO reported deaths and no major safety signals, so any that do emerge are going to be... 9/n

A) probably wrong (if none obvious in 24 million, how many cases needed to prove beyond a shadow of doubt an association is real)
B) vanishingly rare.

So whatever happens from here on in, the risk/benefit is going to be very clearly in vaccine favour even for the lowest risk.