In mathematics, the "delta" is the difference between two different measurements. In today's world, it's the code-name allocated to the mutation of CoVid-19 previously known as "The Indian Variant." It, along with the South African Variant (Beta) and the UK (Alpha) and Gamma (Brazil). It's confusing: there were reports, early on, about many variants including one especially prevalent in Pakistan. They don't have names. And the Greek alphabet doesn't run in parallel with the Roman alphabet so Gamma comes before Delta, providing no help at all to the vast majority of people who want to know which order they were found in.

It is the Indian - Delta version that is, currently, being the most feared, that leads the "variant of concern" notes presenting, WHO says, risks of more serious consequences, higher rates of infection and a reduction in the effectiveness of both treatments and public health measures.

There are more: they are known as "variants of interest." There's Epsilon: it will surprise many that this little known variant was first reported in the USA in March 2020. That was at a time when the USA was, largely, saying that CoVid-19 was someone else's problem. The USA had another new version: Iota, in November 2020. There's the interesting Eta which has, it appears, developed spontaneously in several countries. We say this because, so far, there has been no identification of index cases that can be traced back to one of the various countries that it appeared in at, effectively, the same time.

While it has been said that the change to the new naming convention was to avoid the popularisation of (and for some the racist responses to) terms some deemed prejudicial. It's hard to argue against that when, even today, one can walk into pharmacies and see posters referring to the "Wuhan" virus and former US president Trump's spitting out of the word "Chinese Virus" at every turn, ignoring the medical opinion from within his own country that CoVid-19 had, in fact, been identified - albeit with much later testing of old samples - to have been in the US several weeks prior to the first notified case and to similar evidence in Italy. But there is a pragmatic reason for the change: each variant has a technical name that no one outside the small technical circle can remember or, even, cares about. But now there is more than one American variant and more than one Indian variant. So the names weren't working. And what happens when we run out of letters in the Greek alphabet? We are already half way there, more or less.

Against this, we must set three important facts about vaccination.

1. On every measure possible, it is in the interests of society as a whole to for as many people as possible to be properly and effectively vaccinated even though some may suffer adverse effects. While to say so smacks of the Ford Pinto fiasco, the absolutely minuscule number of cases of serious side effects or, even, death, is a price worth paying - so long as if it is paid, it is properly (not merely adequately) compensated by the taxpayer.

2. The rush to get the vaccines into the arms of as many millions as possible means that testing has been truncated. It has focussed on side effects and not long-term effects; it has also not - because it's impossible - been developed to counter all possible variants. We still do not know how long the protection lasts, how effective it is against variants (that in normal product cycles would have developed before the launch) and we still don't know whether it subdues the virus in the host but still allows transmission. These are important questions.

3. Vaccinations are not a guaranteed method of prevention: there will always be some people who get a virus despite having the full dose. Also, because vaccinations work by giving a person a minute case of the infection so that the immune system can build up "anti-bodies" it is inevitable that some people, following vaccination, will test positive. The stories that side effects are worse for some people after the second dose supports this view.

So, against that highly simplified background, the world is looking for responses, a significant part of which relates to border controls. For example, countries that have concentrated on people farming (tourism) rather than manufacturing or agriculture have fallen into the pit they started digging for themselves in the 1970s. The effect of the decline of tourism is felt fast: in Kuala Lumpur's Jalan Alor, the effects of no tour parties was felt literally the day the tours stopped coming. As a street full of some of the best (and worst) street food on the planet, overflowing restaurants went to serving a handful of customers literally overnight. 18 months on, with Malaysia's borders still closed and with a ban on dining in and the fact that good food doesn't travel well on the back of a motorbike, plus restricted opening hours and the for sale signs have been going up at restaurants all over the city.

Malaysia is far, far from unique. Restaurants with venture capital backing are keeping the lights on, kind of. Independent businesses can't. So international coffee chains, often owned by the owners of shopping centres and therefore can fix their rental positions fire their staff, mothball their outlets or run on skeleton crews and survive; family run coffee-shops and cafés do not. This fundamentally undermines the fabric of society because the same issues are replicated across many sectors of commerce.

That said, border control remains the only defence that governments see as viable, the hiding of an entire country in a silo, breached only by e-communications.