Changes to the travel list have caused huge frustration this summer, with holidays cancelled and plans shattered at short notice.

It has at times drawn consternation, with questions over why countries with lower case numbers than the UK should be effectively off-limits. Some have called for an ‘infections threshold’ above which a country’s status should shift.

But the reality is that case numbers are just one small piece of a complex puzzle used to make travel list decisions. They are made by assessing and balancing risks based on varied and often opaque data, where what we don’t know is as important as what we do know.

A body called the Joint Biosecurity Centre (JBC) has developed the risk assessment criteria. It reviews over 250 countries and territories and presents its findings to ministers who make the ultimate decisions.

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The assessment is a four stage process.

First comes variant assessment – its prominence tells you everything you need to know about how important it is. It includes keeping tabs on transmissibility, how ill people become and whether variants have any resistance to natural or vaccine induced immunity.

Secondly, the countries are ‘triaged’, or assessed on set criteria, with some then being selected for closer inspection.

While those criteria do include case numbers, they also include testing rates, how many cases are being exported to other countries and whether somewhere has the capacity to identify variants using genomic sequencing.

Countries which emerge as contenders for switching to the red or green lists are then given a more comprehensive risk assessment using additional data sources.

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And finally the overall assessment is presented to ministers for a final decision. Things such as travel connections to the UK and vaccination information are included as context.

So, there is a lot more going on than just a straight look at case numbers, and a closer inspection of the data shows why that alone is not enough.

If you were to look just at case numbers, the UK is faring significantly worse than lots of countries on the red and amber lists.

On 4 August the UK recorded 386 cases per 100,000 people, Mexico recorded 122 per 100,000 and Pakistan just 22 per 100,000. But both of these countries are on the red list.

One reason for that could be that they are testing proportionally fewer people. There is likely more virus spreading that is not being detected.

We can tell this by looking at figures that show the proportion of positive cases per tests taken. In the UK on 1 August it was 3.4%, in Pakistan 8.4% and in Mexico an astonishing 41.1%.

Not only has the WHO warned that anything above 5% is concerning, but this data could indicate less robust testing regimes that add extra reasons to be cautious.

Notably countries like India and the UAE that are being upgraded from red to amber had lower proportions than the UK on 1 August.

It’s important to emphasise that travel list decisions are taking into account what we don’t know every bit as much as what we do and that is particularly the case when it comes to new variants.

The UK has some of the best genomic sequencing in the world and we are testing for variants much more than our European neighbours.

From 28 June to 12 July, the UK tested 52,451 genome samples for new variants. Despite faring much better than the majority of the world, France only tested 2779, Spain tested 3211, and Germany just 2319.

To give an even clearer sense of just how little we know about what’s going on in some places, the genome sequencing in India and Pakistan is illuminating.

There has been some contention over why India is now amber while Pakistan remains red, but while India tested 1585 genomes in the latest two-week period for which we have comparable data, Pakistan tested just 19.

If a new variant was taking hold, authorities are unlikely to know about it and this matters in decision making.

Finally of course where new variants are detected it is deemed vital they are kept at bay.

Places where new variants have taken hold are being routinely treated with more caution.

It is telling, for example, that despite cases per tests being similar, Germany has been moved to the green list while France has until now been ‘amber plus’ (meaning even the double jabbed are required to quarantine on return).

This is probably partly because in Germany the Delta variant dominates as it does in the UK.

In France however, 11.6% of cases are now the Beta variant, of which there are a small number of cases in the UK.

That’s concerning because it is believed Beta may have some vaccine resistance.

Similar calculations are no doubt being made about the amount of Beta variant in Spain.

Many more data sets than just these are used to make these decisions, but they are all balancing acts that weigh up risks and probabilities.

The Data and Forensics team is a multi-skilled unit dedicated to providing transparent journalism from Sky News. We gather, analyse and visualise data to tell data-driven stories. We combine traditional reporting skills with advanced analysis of satellite images, social media and other open source information. Through multimedia storytelling we aim to better explain the world while also showing how our journalism is done.

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