Will delayed second doses lead to new variants?

This was an interesting thing to talk about.

First, I'm not an epidemiologist. But, as a Computer Scientist I have a decent backing in math and statistics and on an unrelated topic, a functional understanding of how evolution works.

Yes, putting selective pressure on the virus will increase the odds that a mutation will arise to combat those pressures. The question is really, will it succeed?

And I don't think that the risk is particularly. In fact, I think a successful vaccination campaign is more likely to trigger this.

To understand why, you really need to understand the goal of evolution and what conditions make radical evolutionary changes more likely.

Firstly, evolution is not some "intelligent" process. It isn't like the DNS says "hey look these humans are vaccinating, let's evolve a defence". Rather, the virus is actually mutating all day, every day. Most of these mutations are meaningless. Some will make it less effective. And some will make it more effective, but die off anyway.

The process of evolution is why we exist today. Period. All it "cares" about is propagation of the species. Would being able to evade a vaccine increase it odds of doing so? Not necessarily. Most genetic changes affect multiple aspects, and key evolutionary changes are usually the result of many such changes. And, the virus may become vaccine resistant but at the same lose its virility. Or, it might remain just as infectious, which may also not be enough to guarantee its survival.

Imagine you were born with super human strength. Let's say, you're 10x stronger than the average human. But, there are millions of humans out there. You're all contending for the same supplies. The other humans don't recognize you as one of their own and will attack you on sight. It doesn't matter that you're stronger and better. The existing "strain" of humanity is already quite prevalent and can wipe you out. Even if you co-exist, your DNA is unlikely to take over the human gene pool.

Now, if you were born with that same strength, and something were threatening the human race and your exceptional strength made a significant difference in survival? Then things are different.

Right now, COVID-19 is well established globally. And the biggest tool in its arsenal is how transmissible it is. Variants like the UK and South African strain emerged because social distancing put a serious crimp in the viruses ability to propagate. Vaccines won't play a major role until we get closer to achieving herd immunity. Right now, most strains will find a host easily enough and keep on propagating. This will make it difficult for a mutation to overtake the gene pool. And a faulty vaccine roll out actually helps a bit in this way.

This isn't to say it couldn't happen. Just that it is unlikely to happen as a result of this. Until vaccines are available on a scale where they can be reliably given out to every member of the public, a strain with vaccine resistance alone offers no real advantage over one without it. More than likely strains with vaccine resistance have come into and out of existence many times already. They likely hit a dead end. They ran out of hosts, or ran into a host with a strong enough natural response from another strain to kill it in its tracks.

Without a strong enough advantage relative to existing strains or a strong enough selective pressure it is difficult for new variants to really make a dent in global infections and get a lasting foothold.