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What is the best vaccine against covid-19? Which one protects the most? The percentage of effectiveness is not the only variable that matters

2021-04-13T04:35:09.817Z


The first doses of Janssen, the fourth drug against the coronavirus, to be administered to septuagenarians, arrive in Spain. Its effectiveness, 67%, does not mean that it is worse than the others


Is 90% efficiency better than 70%?

The answer seems obvious, but it is not that easy.

Simple explanations do not usually go well with science.

As inevitable as the preference for the vaccine with the highest percentage published in their studies may seem, they are neither comparable figures nor do they reflect well the risk that each individual has of suffering from covid after inoculation.

Experts insist that any of the approved ones is good and safe.

Spain receives this Wednesday the first shipment of Janssen, the fourth coronavirus vaccine that Europe has approved.

They are the first 300,000 units of the five million that the autonomies will have this quarter.

The criterion for applying this prick is age, as is the case with Pfizer and Moderna.

With more than nine out of 10 people over 80 years old with the first dose of one of these two already inoculated, the Minister of Health, Carolina Darias, announced this Monday that Janssen's would go, in principle, to the next group, the of those who are between 70 and 79 years old, to whom this drug will be combined with the two mentioned.

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Of the four vaccines approved by the European Medicines Agency (EMA), Janssen's is the one that presented the least efficacy in the first results: 67%, by 95% of Pfizer and that of Moderna and 76% of AstraZeneca, according to the latest studies.

But this does not mean that it is worse.

What is efficiency?

These percentages are the first results of the phase III studies that each pharmacist submitted to the EMA.

In these trials, participants are divided into two groups: one is inoculated with the drug and the other with a placebo.

They are experiments with tens of thousands of people who are followed to see how many of them are infected with SARS-CoV-2.

If 10% of the infected subjects were in the vaccinated group and 90% in the placebo, it means that the vaccine is 90% effective.

Can you compare the effectiveness of vaccines?

No. For that, it would be necessary to carry out a single experiment with all the vaccines, applying a vaccine to each group and then checking what percentage of infected is in each one.

But this has not been done: it is practically impossible and impractical in current circumstances.

Each experiment had its own design, a different population context, and different variants of the circulating virus.

They have been studied at different times and places, therefore they are not comparable percentages.

The Janssen vaccine, for example, was tested when the South African and British variants, more contagious and apparently more resistant to vaccines, were already circulating, something that was not happening when Pfizer and Moderna conducted their clinical trials.

As Federico Martinón, head of the Pediatric Service of the Hospital Clínico Universitario de Santiago, indicates, even if the percentages were comparable, they are not really as different as it may seem at first glance.

"If we look in more detail at the confidence intervals, we see that the efficacy is very similar between different vaccines," he adds.

In statistics - and trials are measured this way - the result is not an exact number, but is actually a window on them.

When a vaccine is said to have an efficacy of 76%, it is saying that its results range around 76% (for example, from 71% to 81%), and that interval may partly coincide with that of a vaccine of which It has been said that it has an efficiency of 82%, but whose margin of error makes the result go from 77% to 87%, for example.

That is, if the clinical trials were repeated, the statistical margins indicate that the estimated efficacy values ​​between the vaccines could coincide (in the example above, between 77% and 81%).

In addition, in clinical trials, no vaccinated person died from covid.

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Which is more effective?

Efficacy is the percentage described in clinical trials, a different concept from effectiveness, which refers to the ability to stop the disease in real populations, outside of controlled experiments, which are carried out in healthy people.

It will therefore always be less.

It is still too early to know exactly the effectiveness of each vaccine in a real scenario and to what extent they prevent asymptomatic infections, but what the preliminary results are showing is that all those that are already being deployed have very high percentages when it comes to avoiding the serious illness, enter the ICU and die.

It is also not known how long this immunity lasts, something that only time will tell.

How do I know which vaccine will protect me the most?

Protection against infection is important when studying populations, since if there is a large population vaccinated with highly effective remedies, the virus will not be able to continue spreading. This is known as herd immunity. "The percentages of all approved vaccines are sufficient to achieve this immunity if the majority of the population is inoculated", explains Vicente Larraga, researcher at the CSIC. "Traditionally, it has always been considered that a vaccine with an efficacy of more than 60% is good, and the four that are now in Spain exceed that figure," he adds. But at the individual level, being infected asymptomatically or very mildly is not very relevant; It is much more important to look at the protection against critical illness and death, which according to the data that are known is similar, and very high in all of them.

Source: elparis

All life articles on 2021-04-13

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