A meningitis outbreak is now being treated as a national incident following the deaths of two young people in Kent. This spread, “unprecedented” in the words of Health Secretary Wes Streeting, will resonate with the fears of many parents that they have not done enough to protect their own children from a similar fate. While we have vaccinated them against a large variety of bacteria and viruses which can cause meningitis, we have always known that there are others out there against which they are not protected.

To make matters worse, many of these bugs which cause meningitis are horribly diverse when it comes to how they are recognised by the human immune system. For example, meningococci — the culprits of the Kent epidemic — differ in their “polysaccharide capsule” (imagine a PVC trenchcoat in different colours).

There is a vaccine, MenACWY, which packs a variety of these into a single vaccine — all except MenB, which has proved highly resistant to vaccination. That’s possibly because it resembles some of our native proteins which, naturally, our immune systems are trained not to destroy. The Bexsero vaccine attempts to solve this problem by peeling away the PVC trenchcoat and exposing some of the other garments in MenB’s wardrobe. Although many of these are also quite diverse, the Bexsero vaccine has been able to provide good protection not only against the invasive Group B meningococcal disease but also against the unpleasant effects of infection by a close cousin, the gonococcus.

The Bexsero vaccine has been incorporated into routine infant vaccination since 2015, meaning none of the vulnerable teenagers and university students in Kent would have received it yet. Why? The simple answer is that the health economists in charge decided it would not be a cost-effective strategy to vaccinate teenagers as well as infants. In other words, it would not be worth the number of lives saved within that window of time when those who were vulnerable remained unvaccinated.

These are the sorts of decisions a society makes when debating, for instance, whether to keep cars on the road or to still sell cigarettes. This is not because the victims of these policies are “expendable” — a term thoroughly misused during the Covid-19 pandemic to malign those who warned against the dangers of lockdowns — but because difficult choices have to be made in lean households and lean economies. There is an acute cognitive dissonance in defending the “cost-effective” policy of not vaccinating teenagers with Bexsero while supporting lockdowns — which clearly injured so many of that generation — as a means of limiting Covid deaths.

Britain’s response to the Covid pandemic has entrenched the habit of relying on largely unexamined measures to reduce the eventual burden of disease. There is a fixation on close contact between individuals as the primary driver of deaths when, in fact, it is more likely a gap in immunity which leads to poor infection outcomes. Why do teenagers succumb to this disease and not (typically) older people who are just as active in their habits of swapping bugs? It has to be that younger people are more susceptible: some of them were likely not previously exposed to a sufficient variety of related bugs for their immune systems to recognise the new one which found its way into their throat.

The way to fix this is not by trying to stop the inevitable spread of a new variant by shutting everyone in, but instead to try to protect those at risk. The decision to vaccinate university students in Kent probably comes too late to make a difference. Yet it would be prudent to protect the rest of that age group in Britain, and elsewhere, in advance of the inevitable spread of this strain of group B meningococcus.