**Good Morning. Today I write about the calculations about the risks and benefits of the AstraZeneca vaccine. It is a useful example of how decisions are being made in situations of uncertainty.**

This week the European Medicines Agency has included the possibility that, among the possible side effects of the AstraZeneca vaccine against covid, cases of “very rare” thrombi appear. But it has done so by stressing that the risk is small and recommending that it continue to be used. It is the same as the British agency has concluded, although it makes an exception for those under 30 years of age: the disease caused by the coronavirus is less serious for them, the balance changes and they recommend that priority be given to the use of another vaccine in this group old.

The consequence in Spain is that Health and the communities have agreed not to vaccinate those under 60 years of age with AstraZeneca. It is a simpler decision in our country, for a reason: we have millions of people in their 60s, 70s and 80s without immunization. For now, yesterday Spain has already decided to raise the age to vaccinate with AstraZeneca people from 60 to 69 years old.

But on what do the European and British regulators base their recommendations? His calculations are a typical case of risk analysis.

### UK calculations

The British agency has been exemplary in its communication on this matter. At their press conference they presented some scenarios to compare the small risk of the AstraZeneca vaccine with the benefits it reports, which is to avoid another threat, in this case the one that COVID implies. The results summarized Alexandra Freeman, University of Cambridge, with three charts like this (in English):

The graph compares the risk of contracting the covid in the next four months (and ending up admitted) with the risk of suffering a thrombus with the Anglo-Swedish vaccine, according to his estimate. The conclusion of the study is clear when it comes to the general population: even if the incidence is low, getting vaccinated is better. For people 30 to 39 years it would be 3 or 4 times less risk than exposure to the virus; and for people aged 60 to 69 the risk would be 70 times less. The advantages of being vaccinated are even greater if the incidence rises: if the number of cases is the same as in the United Kingdom in February, the risk posed by the covid doubles that of the vaccine at age 25, multiplied by 10 to 35 and by 200 at 65.

This is how the head of the British regulator (MHRA), Dr June Raine, summed up her results: “The benefits of the AstraZeneca vaccine against covid-19 continue to outweigh the risks for most people.” Their calculations only raise certain dilemmas in the 20-29 age group. That is why the agency proposes to vaccinate that group with the other vaccines. The virus is less dangerous at those ages and if it also circulates little, the risk of the disease is equal to the risk, also low, presented by the thrombi that seem to be associated with the vaccine.

These calculations should be considered approximate, as is evident and emphasized by their authors. For example, they depend on how long the epidemic still lasts. The risk of covid accumulates week by week and month by month, while that of the vaccine lasts a moment: “Its benefits will increase, but the risks will not”, as Freeman emphasizes.

### Some (indicative) calculations for Spain

The previous scenarios can be replicated for the Spanish case. I think it is a useful exercise to understand the decisions of the responsible bodies and not see them as opaque or arbitrary.

**The risk of rare thrombi from the vaccine**

The European agency speaks of 1 case in 100,000 vaccinated. That would be the risk of suffering one of these episodes after immunization with Astrazeneca. The figure is an approximation, like many of those that follow. In fact, the British agency estimates a lower risk -1 in 250,000-, which also modulates by age. Taking these data, we can estimate the risk of suffering a thrombus for three people of different ages:

- π§π» 20-29 years: Risk of 2 in 100,000
- π§π» 30-39 years: Risk of 1.5 in 100,000
- π§πΌ 40-49 years: Risk of 1 in 100,000
- π§πΌ 50-59 years: Risk of 0.8 in 100,000
- π΅π» 60-69 years: Risk of 0.5 in 100,000

**The risk of dying from covid**

It is useful to start with a known fact: the probability of dying from covid. According Imperial College estimates, 1 in 166 infected dies (0.6%), although this fatality varies greatly with age, so that the risk is very different according to groups:

- π§π» 20-29 years: Risk of 30 in 100,000
- π§π» 30-39 years: Risk of 75 in 100,000
- π§πΌ 40-49 years: Risk of 200 in 100,000
- π§πΌ 50-59 years: Risk of 450 in 100,000
- π΅π» 60-69 years: Risk of 1,000 in 100,000
- π΅π» +90 years: Risk of 15,000 in 100,000 (1 of 6)

**Conclution:** The differences are overwhelming. The risk of dying from contracting covid would be much greater than that of suffering a rare thrombus after receiving the vaccine. For people aged 60 to 69, the risk from covid is 2,000 times higher. But the vaccine also reduces the risk to one-tenth for a 25-year-old.

And that’s considering only deaths. The risk of ending up in the ICU is higher. I have estimated it by taking the rates of income for deceased in Spain (ISCIII):

- π§π» 20-29 years: ICU risk of 150 in 100,000
- π§π» 30-39 years: ICU risk of 400 in 100,000
- π§πΌ 40-49 years: ICU risk of 700 in 100,000
- π§πΌ 50-59 years: ICU risk of 1,100 in 100,000
- π΅π» 60-69 years: ICU risk of 1,500 in 100,000
- π΅π» +90 years: (The risk of dying is greater)

**What is the risk of contracting covid?**

In the previous calculation, I compared vaccine and infection, but the risk of covid is reduced if we assume that not everyone will be infected. The problem in this case is to estimate the probability someone has of catching the virus, which is something individual (a borderline case is people who have already passed it) and which depends on the incidence according to place of residence or period of time (how Are we going to estimate the risk of contagion this summer or in 2022?).

Let’s do like Cambridge’s work: let’s think about the risk of four months with an incidence like the one that exists now in Spain, which is around 500 infections per month per 100,000 people. In this scenario, it is enough to multiply the previous risks by the probability of contagion, which we have estimated at 2% (2,000 out of 100,000) during that period of time.

So, the risks of dying from covid in four months would be:

- π§π» 20-29 years: Risk of 0.6 in 100,000
- π§π» 30-39 years: Risk of 1.5 in 100,000
- π§πΌ 40-49 years: Risk of 4 in 100,000
- π§πΌ 50-59 years: Risk of 9 in 100,000
- π΅π» 60-69 years: Risk of 20 in 100,000
- π΅π» +90 years: Risk of 300 in 100,000

And those of going through the ICU:

- π§π» 20-29 years: ICU risk of 3 in 100,000
- π§π» 30-39 years: ICU risk of 8 in 100,000
- π§πΌ 40-49 years: ICU risk of 14 in 100,000
- π§πΌ 50-59 years: ICU risk of 22 in 100,000
- π΅π» 60-69 years: ICU risk of 30 in 100,000
- π΅π» +90 years: (The risk of dying is greater)

**Conclution:** The difference for people in their 40s or 60s is still very clear; the risk of ending up in the ICU due to covid would be 14 and 60 times higher, respectively, than that of suffering a thrombus after being immunized. They are very big differences. But as happened in the Cambridge calculations, for young people there is already a certain dilemma and the risks associated with the vaccine and the infection seem of the same order of magnitude.

However, the vaccine has two other benefits.

On the one hand, the passage of time. If we think that the risk of contracting covid in the coming months rises to 10% –this is the people who have been infected since last August – then the risk of ending up in the ICU for a young person of 20 or 29 years old would rise up to 15 per 100,000, which is again clearly greater than the risk of thrombi.

The other benefit is social. We have done the individual calculations, but another advantage of the vaccine is that it reduces the likelihood of third parties getting infected. When someone gets vaccinated, they do a bit to protect everyone, literally.

Lastly, I will stress that these numbers are only an exploration. They are an exercise, hopefully useful, in understanding the type of dilemmas we face and the type of analysis that regulators do. But the precise calculations will be yours.

### More stories this week

**In which countries is mobility reduced the most?** We have built a map of Europe with 800 regions – I think unpublished – from Google data of trips to work, stations, bars. I loved doing this story, with Daniele Grasso and Borja Andrino. These are data that had not been seen and in which we found quite a lot of interesting things.

**This is how the most ambitious vaccination in history progresses:** in three months 7 doses have been given for every 100 people in the world. A review of country-by-country data. The last graph, of vaccinated by age, has a lot to do with the dilemmas posed by AstraZeneca that I discussed earlier.

**What do the polls say in Madrid?** This week the CIS poll was moving away from the average by raising the sum of the lefts, but I read that with skepticism: it is a pattern of years that has often failed. My analysis of that and other keys.

**Can you help us?** Forward this newsletter to your contacts or tell them to sign up here. You can write to me with my email: [email protected]*.*

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