Things are going according to plan. Despite a few wobbles about vanishingly small blood-clot risks, our vaccine rollout charges forward. And tomorrow we will enter the next phase of our roadmap to freedom.

But at the Downing Street press conference last Monday, England’s Chief Medical Officer Chris Whitty was circumspect. Moving ‘steadily’ was key, he said. ‘Just because you vaccinate lots of people [doesn’t mean] the problem goes away.’

He pointed to the South American state of Chile as an ‘extreme’ example of this. So what is going on there?

Like us, Chile began vaccinating in December. They have now jabbed roughly a third of their 19 million population at a rate faster than the rest of South America. Only Israel, the United Arab Emirates and the Seychelles have fully vaccinated a larger proportion of their populations. Yet today, Chile is seeing a terrifying surge in cases.

In the past week, the country has recorded more than 50,000 new Covid infections, with deaths creeping up to more than 600 a week.

In the capital, Santiago, the hospitals’ intensive-care wards are at 95 per cent capacity. Why have cases there continued to rise sharply?

According to Chilean experts, there are a number of obvious explanations. ‘We eased restrictions too early,’ said Dr Claudia Cortes, an infectious disease specialist at the University of Chile.

‘Our vaccination plan has been very good, but management of the general population has been poor.’

In January, just weeks after they began jabbing, the Chilean government eased the strict travel restrictions that had been in place for nearly a year. Citizens were permitted to travel abroad for holidays.

A destination that is particularly popular with Chileans is neighbouring Brazil – which has a highly infectious variant.

This week, Brazil recorded more than 90,000 new Covid cases in a single day and is currently seeing in excess of 4,000 daily deaths.

Brazil’s pandemic death toll is nearing 340,000 – second only to the 572,000 total deaths so far in the United States.

Despite this, Chile did not stop travel between the two countries until last Monday. This potential influx of infections added to existing difficulties.

In Chile, people who wished to travel outside their own local area were required by law to fill out an online form, stating where they were going and how long they would be gone for, and obtain a permit.

Yet the authorities failed to enforce this, says Dr Cortes. ‘We had millions of people travelling unchecked between cities, bringing infections with them.’

On March 1, even as cases were beginning to rise again, Chile announced the reopening of leisure venues and businesses. While the government continued to recommend social distancing and mask-wearing, the guidance was flouted.

Dr Cortes said: ‘It was as though the pandemic had just disappeared, young people were packed into bars and restaurants. There was no social distancing, no mask-wearing.’

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On March 28, Chilean authorities finally introduced new lockdown measures, ordering residents to stay home, apart from twice-weekly trips to essential shops for food and medicines.

Now, anyone entering the country must stay in a quarantine hotel for five days at their own expense. But many are still refusing to take the emergency seriously.

‘Every night we hear stories of illegal parties being broken up,’ says Dr Cortes. ‘Churches are holding illegal services. Businesses are classing their workers as essential so they can still travel to the office. People don’t realise what’s going on inside the hospitals.’

Martin Hibberd, Professor of Emerging Infectious Disease at the London School of Hygiene & Tropical Medicine, said it was clear from the outset that Chile was moving too quickly.

‘Even now, Chile has vaccinated only a third of its population. That was never enough to prevent infections surging with no other measures in place. And once infections go up, you can’t bring them back down again with vaccines alone.’

The situation looks very different in Israel, the world leaders in vaccination. Israel has now vaccinated more than 60 per cent of its nine million population with two doses, and removed nearly all restrictions at the beginning of March. Since then, cases have continued to fall and are now at a low of fewer than 300 new infections a day.

...between a blood clot and an embolism?

Blood clotting is a normal response to an injury. When the body is wounded, compounds are released that cause blood cells to clump together into a solid mass, limiting blood loss.

But blood clots can form inside an artery or vein and block the circulation, or break apart and travel through the circulation, blocking the blood supply to a major organ such as the brain, with fatal consequences.

The term ‘embolism’ is usually used to describe this serious blockage in blood supply. A pulmonary embolism occurs in the artery that carries blood from the heart to the lungs. An embolism can also refer to a blockage caused by an air bubble or a foreign body.

So where does this leave the UK? Three-fifths of all British adults have now had at least one vaccine dose, and we are told there are more than enough doses to offer all adults a jab by July.

Cases are continuing to fall, with fewer than 3,000 new daily infections, down from a high of 61,000 in January. But with the largest easing of restrictions yet starting tomorrow, with the return of shops, hairdressers and outdoor dining, scientists believe the UK is likely to see cases begin to rise again.

Does this mean the UK could be the next Chile? Prof Hibberd thinks not – as long as the Government ignores calls to ‘unlock faster’. He said: ‘We’re more like Israel, because we are cautiously easing restrictions as we vaccinate, rather than removing them all at once. Cases will rise, but if we are cautious it will be manageable.’

Some scientists have pointed to the differing vaccines and variants in the two nations to explain their polarising fates. While Israel is using the Pfizer jabs exclusively, Chile has primarily been offering the Chinese-made Sinovac, a cheaper alternative that can be stored in a regular fridge.

Studies suggest Sinovac is only 50 per cent effective at stopping infections of the Brazil variant. While it is still thought to give strong protection against serious illness, this means their jab may be ineffective at halting the spread of coronavirus. If this is the case, it may be cause for further caution here.

The Oxford-AstraZeneca vaccine is often described as the Western version of Sinovac, and studies have suggested it is also less effective against the Brazil variant.

Prof Hibberd believes these worries are not helpful. He said: ‘Right now, there’s lots we still don’t know. We don’t know whether the AstraZeneca vaccine really is less effective against the Brazil variant. What we do know, though, is that Chile opened up international travel and removed social restrictions. If there’s a lesson to be learned here for the UK, it’s that we need to be careful in doing these things.’