There is a convention in certain British newspapers that whenever a property is mentioned ¨C no matter what the context ¨C its value must be given.

The result is that a story about a gruesome murder will take a sudden diversion into?house prices in rural Hampshire, before returning to the grisly business at hand.

A similar rule is often applied to international students: whatever the story, reference must be made to the income they generate for the university and the wider economy.

Both are understandable in their way. Anyone who has lived in the UK will know that property prices are right up there with the weather as dominant strands in the national conversation, controlling innumerable aspects of life and economics.

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Similarly, in many anglophone universities the simple reality is that over a couple of decades, international students have inexorably become one of the central planks of the business model. Without them, the numbers fail to add up and the system crashes.

Until early 2020, beyond a general sense that there was perhaps an over-reliance on students from particular countries (China and India being the two most dominant by far), it was a system?that seemed, if not optimal, then at least manageable.

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The continued growth?in demand for international study opportunities was baked into the global demographics. Developing economies had more and more young people, with greater access to finance, burning with the aspiration that is common to emerging middle classes the world over: to better themselves through further study. It was a rock on which to build, and universities did.

Then the pandemic hit, and while the wheels did not exactly come off, they did jam alarmingly, and few would argue that we are yet back to smooth operation of business as usual, especially in countries such as Australia and New Zealand, where borders remain largely closed.

There also remains great uncertainty about the future intentions of school-leavers who may have got used to alternative models, and the views of parents will continue to be instrumental too.

Talking recently to one vice-chancellor, I asked how likely he thought a rebound in demand from China was. ¡°If I was a parent looking at the headlines about the UK as a plague island with empty supermarket shelves and tens of thousands of Covid cases a week, I am not sure I¡¯d be sending my only child off to study here,¡± he said.

These issues will, one hopes, ease as the pandemic is brought under control and we learn to live with its legacy, and some countries with the toughest restrictions are now starting to loosen up.

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The US is opening up travel to vaccinated incomers from many parts of the world, while last week Australia¡¯s most populous state??that?it would be seeking to bring international students back for in-person study this side of Christmas.

To a certain extent, this is driven by financial necessity ¨C those mind-boggling numbers attached to all commentary about international study are not entirely made up.

But the importance of the international flow of talent, ideas, cultures and understanding goes far beyond the profit and loss accounts of universities, as anyone who works in one will understand.

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In our cover story this week, we seek to answer the (possibly unanswerable) question of how many international students is optimal ¨C not just financially, but in all its many aspects.

The idea that there could be too many international students is a concept some will bridle at, but in any case it is a problem that many universities would like to have.

They are not helped by headlines such as those that appeared in the last week, warning that Indian students vaccinated under the Covishield programme were not having their vaccination status acknowledged by the UK under its updated travel rules (despite Covishield administering effectively the same jab that has been given to the majority of the UK population).

The problem was , but these administrative slights matter. If countries that have so benefited and, yes, relied on this flow of international talent are to recover their former position, we must restore a true sense of welcome ¨C the idea, as one Australian university leader puts it in our feature, that these young people investing their future as well as their money in our universities are ¡°a gift¡±, not simply a mark on a financial ledger.

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john.gill@timeshighereducation.com