Do we need a fourth vaccine dose, and if so, which?

I have been trying to decide whether to get a fourth dose of the COVID-19 vaccine. Yes, a FOURTH dose - the very essence of a first world problem!

I am technically eligible, here in Ontario, five months after my third dose. However, while the third dose was a no-brainer - all the evidence showed two doses rapidly declining in efficacy, and a third dose boosting it back up into the 90% range - the jury seems to be still out on the case for a fourth dose. Most studies do show that the third dose starts to lose efficacy very rapidly day after about 3 months, and is all but gone by 6 months.  It does seem reasonably clear, though, that just repeating doses of the original formulation will have increasingly marginal efficacy, and may even impair our immune response.

On the assumption that the current Omicron wave (the 6th, is it?) will peter out as the warmer weather gathers steam, as in past years, the likelihood is that a new wave will arrive with the cooler fall weather. However, it's anyone's guess what variant that will involve - Omicron? Omicron+? A completely new variant (Sigma? Tau?) We can't predict it, and vaccines aimed at specific variants take too long to develop and test to wait and see.

It seems likely to me that the next wave will be either Omicron (BA.1 or BA.2 or BA.n) or a new variant that is at least much more similar to Omicron than to the original "wild-type" virus, or early variants like Alpha, Beta and Delta. Pfizer and Moderna are apparently already testing vaccines against Omicron (although some early results are disappointing, and early estimates of a March release date have obviously not panned out). It's not clear when these will be available, but I'm tempted to wait for them, rather than take yet another dose of the original one. 

When third doses became available, experts were advising not to wait for an Omicron-specific vaccine, but the case for a fourth dose is quite different, it seem to me. The virus is now so different from the original version that a more targeted vaccine -  or at least a "bi-valent", or mixed, vaccine like Moderna is supposedly well advanced in developing  - makes more sense to me. And I can certainly wait a few more months... And now, the US's CDC has changed their advice, and is recommending that people wait until the fall for a second booster (possibly a variant-targeted one), unless they are at high risk.

In the meantime, can we give all the millions of vaccine doses we have sitting around to countries that can use them? They may not be the most current vaccines, but they are certainly better than nothing.