How does the government decide which countries are on the red, amber and green lists that determine which countries Britons should or shouldn’t visit – or rather what kind of quarantine they have to undergo when they return?

The question is of more than academic significance, given the controversy over Britain’s decision on 2 April to put Pakistan and Bangladesh on to its “red list” (which compels travellers from those countries to quarantine in a government-endorsed hotel and bans those without citizenship or residency), but to delay putting India on to that list for another two-and-a-half weeks.

That decision matters because during that period, thousands of travellers from India arrived in the UK – including a particular rush in the three-and-a half days between the decision to red list India being announced and it being implemented.

Many of those travellers, we now know, were not just suffering from COVID-19 but from the B.1.617.2 (Indian) variant which is believed to be more transmissible than the variants currently in the UK.

Live COVID updates from the UK and around the world

There are now known to be multiple cases of this variant in various spots throughout the country.

Having become the dominant strain in Bolton, Blackburn with Darwen and surrounding areas, more recent data suggests it appears to have spread elsewhere, with significant proportions detected in Bedford.

The chief medical officer believes the variant will soon become the dominant variant in the country.

It is going too far to say this would never have happened had India not been added to the red list sooner; it is quite likely that this variant would eventually have spread to the UK.

Subscribe to the Daily podcast on Apple Podcasts, Google Podcasts, Spotify, Spreaker

However, there is little doubt that its arrival could have been delayed. The UK has detected significantly more instances of the three Indian variants than any other country in Europe.

This was not, in other words, inevitable.

It is also too early to say whether this will, or will not, cause further cases and deaths of COVID-19.

Case numbers in the UK are still very low. The vaccination programme is proceeding faster and with more coverage than almost any other country in the world. And the vaccinations themselves seem to be effective against this variant.

So there are reasons to be hopeful.

Even so, the speed with which the variant has established itself in this country is at least in part likely to be due to that fateful decision to put India’s neighbours on the red list and to leave India on the amber list for a crucial period in April.

While amber list status still compels travellers to self-isolate and to take coronavirus tests, it is, by definition, more porous and more reliant on trust than the red list hotel system.

Which brings us back to that question: how does the government decide which country is in and which is out?

We’ll get to the official answer later, but first let’s consider what Health Secretary Matt Hancock said today when asked about this in the House of Commons:

“The truth is, that when we put Pakistan on the red list – and indeed Bangladesh – the positivity of those arriving from Pakistan and Bangladesh was three times higher than that from India.

“That’s why we took those decisions… It’s all very well to ask questions with hindsight but you have to base decisions and policy on the evidence at the time.”

This is helpful on a couple of fronts. First, it makes it pretty clear the decision was not based, rightly or wrongly, on variants but on the prevalence of COVID-19 in these countries more widely.

Except this is, well, odd.

Because as the press release told us at the time, the decision was taken entirely because of the proportion of variants coming from these countries.

There is no mention whatsoever of the proportion of people testing positive. Anyway, let’s gloss over that one and move on to the data.

Because the second helpful thing about this statement was that Mr Hancock provided some data – or a hint of it – which might allow us to compare notes.

And, as it happens, the NHS has just released a dataset which shows us the average positivity rate (in other words what Mr Hancock is referring to) and the number of variants of concern or interest being brought by travellers into the UK.

This dataset is very important since as we all know by now, the COVID data in some countries is not especially reliable.

Here, we have a dataset which presumably contains every traveller coming from those countries, and allows us to get a sense of just how much COVID-19 they’re bringing into the country.

Except that that dataset – which presumably constitutes the “evidence at the time” Mr Hancock was referring to – tells quite a different story to the one he referred to in the Commons.

It shows that in the period from 25 March to 7 April, some 5.1% of passengers coming to the UK from India tested positive for COVID-19, not far below the 6.2% level recorded by passengers from Pakistan, and comfortably higher than the 3.7% of passengers coming from Bangladesh.

This, remember, is for the period at the very beginning of April, two weeks before India was put on the red list.

And far from being three times higher than in India, the COVID positivity rate in Pakistan was only slightly above India; the rate of passengers coming from Bangladesh was considerably lower than that of those coming from India.

Now, it’s quite possible Mr Hancock is referring to another dataset that hasn’t been publicly released. It’s quite possible he’s referring to data from earlier in March.

But note that we’re talking here about the very same period during which the decision was taken to put Pakistan and Bangladesh on the red list.

We’re talking about data collected by the government itself.

And we’re talking about a period weeks before India was eventually put on the list.

Odder and odder.

I should say I’ve reached out to the Department of Health and Social Care (DHSC) for an explanation, but at the time of writing no explanation has been forthcoming.

But leaving aside the specificities of this case, it nonetheless underlines a broader point: There seems to be little clear rationale out produced by the government about why certain countries end up on the red list and others don’t.

If you browse government’s websites, you can find plenty of broad-based discussion. According to this page, there is a “dynamic risk assessment methodology to inform ministerial decisions on red, amber and green list countries”.

Certain datapoints are considered, including testing rates, incidence rate, test positivity, evidence of variants of interest or concern (such as the Indian variant).

The problem with this information, is it is hopelessly vague.

There are no specifics about, for instance, what level of COVID-19 positivity would push a country from one status to another. Nothing about the extent to which variants are the concern.

And where data is provided on decisions, such as on this page, it is partial and not especially enlightening. Not every country is covered. Very few datapoints are provided. It is, in short, clear as mud.

Nor, that I can see, is there any simple way of reverse-engineering a formula which would link decisions to data.

Let’s go back to that dataset of COVID-19 cases among travellers coming from various different countries into the UK.

It shows, for instance, that the average positivity rate among travellers coming from Mali and Yemen in late March/early April was a whopping 20%.

In Libya, the average was 19%; in Cameroon it was 12.2%.

Now there are all sorts of questions raised by these numbers, especially given – according to the official data from each of those countries – none of them have especially high COVID-19 rates.

But the other thing these countries all have in common is that none of them are on the UK’s red list.

They are all still, like India before its ban, amber listed.

Now, it’s true there are no flights between them and the UK, but then other countries which don’t have direct flights to the UK – places like Angola and the Democratic Republic of Congo. That might be the explanation.

But since the government is so opaque about why it’s making these decisions, it’s hard to say for sure.

Consider another example: the Philippines. It was added to the red list along with Bangladesh and Pakistan, the explanation (at the time at least) being because of the number of variants of concern coming from there.

And delve into the dataset and that is indeed borne out by the evidence: as of mid-April the percentage of COVID-19 cases detected on travellers coming from there was quite low compared with other countries – only 2%.

But now look at the proportion of those positive cases testing positive for variants of concern or interest and you find that it was 75%.

But if you’re going to put the Philippines on the list, then why not add Ghana too, which not only has a slightly higher positivity rate (eg more prevalence) but also a greater share of variants: 80%?

Why does the UAE remain on the red list despite travellers from there having lower COVID positivity levels than most of Europe?

Doubtless there are answers to questions such as these, but the government is providing very few of them.

And when they do provide explanations, as Mr Hancock did today, they sometimes do not accord with the available data.

Related posts:

Vaccinated people should be able to meet up and go on holidays, says scientist Honda’s Swindon plant secures new future with promise of ‘thousands’ of jobs ‘Mini’ COVID-restricted Queen’s birthday parade takes place at Windsor Castle Man charged after teenager fatally shot in the head ‘We stand with you Marcus’: Messages of support for Rashford as artist repairs vandalised mural F1 driver Lando Norris left ‘shaken’ after watch stolen at Euro 2020 final Brown crabs mesmerised by underwater power cables for renewable energy sources, study finds Ministers urge parents of secondary and college students to ensure they test regularly and get vaccinated Lesbian couple welcomes ‘overwhelming’ support for challenging NHS fertility policy described as ‘£50,000 gay tax’ Two storms to hit UK within three days as forecasters warn of 90mph winds and ‘blizzard conditions’ Former Man City doctor fell 100m to his death from spot where he proposed to his wife 27 years earlier All Northern Ireland COVID legal restrictions downgraded to guidance only