These new, more contagious variants were inevitable, as discussed here. The more time we give the virus to mutate, the more mutations will occur, the more bad mutations will occur, and the worse the overall outcome will be for our health – individually and as a society. These new variants are evidence of the process I described at work. Had we eliminated the virus before now, we wouldn't be dealing with this problem.
For clarity, the new, more contagious strains that I’m referring to are the UK (B.1.1.7), South African (B.1.351), and Brazilian (B.1.1.248) strains.
The Virus Was Always Mutating
Once we decided that we wanted to keep this deadly, destructive pathogen circulating in our communities, it became inevitable that the virus would eventually mutate in ways that would make it more contagious, and more harmful to us. These new strains are the clearest demonstration of that process, but they are not new developments or isolated incidents.
The process of mutation in the virus is constant, and it occurs along every possible axis. Every characteristic of the virus that can mutate, will mutate. Any trait that can be influenced by natural selection will be honed to the virus's advantage. For example, it is likely that the virus has become more airborne over the last year, as the mutations that were able to hang around in the air longer, were more likely to be picked up to seed new infections. Those new infections will retain that desirable trait and this is how natural selection ensures that the virus will become more airborne, more contagious, and more virulent over time.
The New Variants ARE More Deadly
The new strains pose a greater threat to our health; both as individuals and as a collective. Even if the incident fatality rates are no higher, these strains are still more deadly. The overall threat posed by the virus is determined by the damage it can do to your health and by your likelihood of catching it: health risk = probability of catching it x probability of dying. Your likelihood of catching the virus just increased, so your risk of dying from it did too. Your personal risk is higher and, as the virus is now more contagious, our societal risk is higher too.
And these effects aren’t small. A strain that is 50% more transmissible presents a significant increase in society-level risk because the effect compounds across all interactions. An individual that is infected with the new strain might pass it on to 50% more people (say, 3 instead of 2) but those people are also 50% more likely to pass it on. So, after two rounds we have 9 people infected instead of 4. This 50% figure isn’t simply the increase in the probability that you will catch the virus; it is a national threat that guarantees that significantly more people will die.
Post Script: The UK's expert advisory group has stated that there is a realistic possibility that the new variants are associate with a higher overall risk of death.
The New Strains Will Become Dominant
More contagious strains will always become more dominant. They will outbreed the existing strains and will asymptotically approach 100% of all cases in Ireland. There are two factors at work here. Firstly, the new strains will drive the increase in the overall number of cases, which necessarily gives them a larger share over time. Secondly, they will gradually displace existing strains, as those at risk of infection are more likely to be infected by the more contagious strains first.
The new strains will create more infections overall, and they will compose a higher and higher proportion of those infections – at least until the next major mutation comes along to replace them. With another 9 months to herd immunity via vaccination, we can expect another – even more dangerous – round of mutations. The longer we let the virus hang around, the more bad news to look forward to.
Herd Immunity is Even Further Away
The proportion of the population that defines the threshold for herd immunity is a function of the transmissibility of the virus.
If the reproductive number for the virus is 10, then each infected person will transmit the virus to 10 other people, on average. However, if 90% of the population is vaccinated (or otherwise unsusceptible), then each infected person will only be able to transmit the virus to one other person, since only 1 in 10 will still be susceptible. That susceptible, and now newly infected, person would find themselves in the same situation, passing it on to only one other person so the effective R would be 1. If vaccination was higher than 90% of the population, then the effective R would be less than 1, the transmission would decline and the outbreak would be brought under control. You can read a longer explanation of herd immunity here.
As a rule of thumb, herd immunity is achieved when at least (1 – 1/R)% of the population is vaccinated. That number is increasing in R, so the higher the R, the higher the percentage of the population that needs to be vaccinated and the longer it will take to reach that point. Herd immunity is now further away than it was before these strains came along. Which means the virus has more time to mutate, which means...
More Bad News – The Unknowns
It’s worth highlighting the things that we don’t know about the new strains.
We don’t know whether our vaccines will work as well on the new strains as they did on the previous versions of the virus – the one on which the vaccines were trialled. The new strains could make the vaccines less effective – either evenly, or on particular cohorts. They could require new vaccine designs, which will take time to develop, trial, and authorise. Or they could make one, or all, of the vaccines completely useless, in which case we would have to start our search for vaccines again.
That last possibility seems extremely remote, but the other two are feasible. That is not to say that they represent a serious threat to our ability to vaccinate the population, but if they make the current vaccination program less effective, they will add to the time required to reach herd immunity. Even a loss of a few percentage points, say from 90% to 85%, is enough to add a meaningful amount of time to the wait.
There are also suggestions that the new strains may make our existing diagnostics less accurate. The higher the probability of false negatives, the less control we have over the outbreak, which would be more bad news again. I hope that is not the case.
Finally, these mutations may increase the risk of reinfection. It’s only a tiny percentage of people who have had confirmed reinfections, but those numbers will almost certainly increase, because, as we know… if it can happen, then it will!
Putting that all together and we can see that these mutations will lead to more infections, more deaths, and a longer route to herd immunity. I'd say we're still at least 8 months away, so that gives the virus more than enough time to produce another round of major mutations which could delay us again.
This has the potential to a long, painful, drawn-out process. Are we really sure that elimination isn't possible?
 The true threshold for herd immunity depends on the reproductive number which in turn depends on multiple factors, including the number of people who are already immune or otherwise unsusceptible, the distribution of those who are susceptible, and environmental and behavioural factors, notably restrictions. Once the restrictions are lifted, people will have more contacts, and R will increase, so this formula is best thought of as a minimum that would need to be surpassed.