Smallpox vaccines are widely available, for now

I independently have been casually suggesting getting the vaccine to several of my friends and family. 

Immunity against any orthopoxvirus is immunity against all of them. From monkeypox to cowpox to horsepox to camelpox to Alaskapox to half a dozen things that only virologists have ever heard of to God knows what relatives are floating around the virosphere under the radar. Between their exceptionally low mutation rate, their huge genomes giving a large attack surface to T-cell reactions, and the fact that there's more than a dozen surface proteins any one of which getting neutralized kills it dead, these viruses simply can't evolve around immune reactions even on timescales of tens of thousands of years. The monkeypox outbreak probably was able to finally take off human to human in 2017 in Nigeria because of the combination of an ever growing population that has never been vaccinated against smallpox and the aging population that did get it having effectiveness against infection slowly fade on a timescale of decades. I think this pre-emption of other potential orthopoxviruses rather than smallpox or necessarily even monkeypox is the strongest argument. There is an open immunological niche left behind from the eradication of smallpox and the cessation of vaccination, just waiting for something to fill it.

It should be noted that what is being offered is the third generation smallpox vaccine, also known as modified Vaccinia Ankara.  It is a live attanuated vaccine, unlike the first and second generation vaccines which are just giving you a localized vaccinia infection. Ten years of passaging in chicken cells has left the attanuated virus unable to successfully replicate in mammalian cells - it invades cells, and turns them into virus factories, but the resultant virus particles fail to successfully go through the final maturation step and are sterile. Since it doesn't establish actual replicating infection it is much much safer, but is a bit less immunogenic than the old school version. Has to be propagated in primary chicken fibroblasts, making production annoying compared to mammalian culture of ordinary vaccinia. 

In addition to the benefits of the third generation smallpox vaccine in and of itself, it should also make any future doses with the old-school smallpox vaccine (which is more effective and might work for longer and is easier to grow in culture and thus more likely to be widely deployed in a future biosecurity scenario) no longer dangerous. Any immune memory to orthopoxviruses nearly eliminates the possible systemic Vaccinia infection outcomes that can happen your first time getting it.  One course of what they're giving out now should be very effective against bad outcomes to any orthopoxvirus for a very long time, but I know that after a few decades regular vaccinia got a bit leaky at preventing infection outright and they regularly revaccinated doctors. In this monkeypox outbreak vaccines that were 50 years old were only somewhat effective against infection risk.

I got the vaccine this summer, as did two people I know who like me actually did qualify according to the letter of the local rules. No interesting reactions. With the local rules slackening and demand falling and monkeypox all but eradicated in North America such that getting a dose now is not taking protection from someone who may have needed it this last summer, I have already been suggesting getting it for more people I know.  Of course, I am a bit of an antibody hoarder with multiple elective vaccinations in my history and even more I wish I could get, who thinks about resilience a lot.

That's mildly interesting about smallpox vaccine being unusually easy to get right now, but doesn't answer the prior question about whether one should if one could: smallpox vaccination lapsed, even though the risk of accidental/deliberate release never went away, because it does have a certain rate of side-effects. How should one think about the risk of outbreak and benefit of being pre-vaccinated and does it really lead one to do so for (non-monkeypox) reasons?