The value of truth diminishes

Corona check: the truth about the effectiveness of vaccines

Berlin - At first glance, the matter seems clear: If a corona vaccine has an effectiveness of 95 percent, then it protects 95 out of 100 people vaccinated against corona. Or? The short answer is no! It is correct: An effectiveness of 95 percent means that the vaccination reduces the number of sick people by 95 percent - i.e. from 100 without vaccination to 5 with vaccination.

"It is not 5 out of 100 vaccinated people who get sick, but far fewer," explains Wolfgang Becker-Brüser from the specialist journal Arzneitelegramm. The effectiveness of a vaccine should not be viewed as that of a drug that has a therapeutic effect. However, a vaccine has a prophylactic effect. “Of the thousands of volunteers who take part in vaccination studies, only a few people get sick anyway. And only these few sick people are included in the effectiveness assessment. In order to assess the effectiveness, the decisive factor is how well a vaccine reduces the risk of disease in this group, ”explains the doctor and pharmacist.

The fundamental difference: The wrong first "interpretation" describes one absolute risk reduction, which refers to the number of people vaccinated. In the clinical studies on the effectiveness of the corona vaccines, however, values ​​for relative risk reduction collected - it is about the extent to which a vaccine protects against disease compared to a placebo vaccination. The value relates to the number of sick people and not to those who have been vaccinated.

Constructs such as relative risk are not easy to understand for many people. "In training courses I regularly experience that even medical professionals often have difficulties with the correct interpretation," says psychologist and risk researcher Gerd Gigerenzer from the Max Planck Institute for Human Development in Berlin.

So it's high time to shed some light on the subject. Because in the discussion about the corona vaccines approved so far and the question of whether some products are possibly second-rate, a lot is dealt with with efficacy. And those who do that should know what they are talking about - and acquire risk expertise, as Gerd Gigerenzer calls it. The long answer to that.

The basics: how effectiveness is determined

First of all, you should be aware that the efficacy values ​​are not set in stone, but are the best possible in the approval phase. The more people vaccinated as part of the ongoing studies, the clearer the picture becomes over time. However, the approval data is quite meaningful and allows comparisons because there are conditions that all developers must adhere to. This includes, for example, that in clinical phase 3 the vaccine is tested on more than 10,000 volunteers who are at risk of infection. And there is always a comparison group that receives a sham vaccine (saline solution) or an already approved vaccine against another pathogen (for example meningococci).

The subjects are examined by a doctor and laboratory medicine at certain intervals. Observation must last at least six weeks after the second vaccination. And a certain number of illnesses must have occurred in order to be able to make any statements about effectiveness and safety. The studies primarily focus on the question of how well a vaccine protects against Covid-19. This is determined by comparing vaccinated and non-vaccinated people. If the same number of subjects in the group of vaccinated subjects contract Covid-19 as in the comparison group, the vaccine has no effect. If, for example, out of every 100 people without vaccination, two get sick, then 50 percent effectiveness means that only one gets sick with vaccination - the relative risk is halved, the effectiveness, also known as efficiency, is 50 percent.

Astrazeneca's vaccine: preventing severe Covid-19 courses

Things are a little more complicated with the vector vaccine from Astrazeneca and Oxford University. In the studies relevant for approval, it has shown an average effectiveness of 60 percent. Of the four studies carried out with a total of around 24,000 participants, the European Medicines Agency (EMA) only considered two because fewer than six Covid-19 cases each occurred in the other two studies. The two studies relevant to the assessment - they were carried out in Great Britain and Brazil - showed an effectiveness of around 60 percent. In absolute numbers: 64 Covid infections occurred with the vaccine among 5258 test persons; in the group of 5210 people who had received a sham or other vaccination, there were 154 Covid cases.

Because most of the study participants were between the ages of 18 and 55, the EMA saw, as it announced at the end of January, that it was unable to quantify the effectiveness for a group of people over the age of 55. Nevertheless, it did not limit the age of approval because the results basically suggest a similar effectiveness. Efficiency values ​​for older people are simply still pending. That was also the reason for the German Standing Vaccination Commission (Stiko) to recommend the Astrazeneca vaccine only up to 65 years of age. Apparently the Stiko is already considering changing that.

The RNA vaccines: that was the registration dates

The facts are clearer with the two RNA vaccines approved in the EU from Biontech / Pfizer and Moderna. The Biontech vaccine Comirnaty reduces the disease risk by 95 percent, that of Moderna by 94 percent. The US company Moderna submitted data from studies with a total of 30,000 participants for approval, while Biontech provided more than 43,000. Appropriate numbers of older age groups were represented in both studies.

The result at Biontech is converted to 10,000 people: With a sham vaccination, 93 Covid diseases occurred out of 10,000 people, with a vaccine, however, only 5. With Moderna, there were 8 diseases per 10,000 people with vaccines compared to 133. The Astrazeneca efficiency also leaves nothing to be desired convert to 10,000 people: Then there are 296 diseases in the placebo group - and 122 in the vaccinated group. Even with an efficiency of 60 percent, a very large proportion of the people are spared from Covid-19.

Protection against serious problems: an aspect that deserves more attention

But that's not all that should be considered when making a vaccination decision. While there is widespread discussion of the as yet unresolved question of whether vaccines also induce so-called sterile immunity, i.e. not only protect against symptomatic infections but also against asymptomatic infections, another aspect has received too little attention so far: protection against serious and fatal ones Gradients. For all that is known about the three vaccines so far, they are extremely effective in preventing these particularly dreaded events.

All symptomatic infections - from mild to severe - were counted as Covid 19 cases in the studies. In addition to a positive PCR test, symptoms such as fever, cough or shortness of breath had to be present. A severe course was when treatment with oxygen was necessary, lung failure occurred or a patient was transferred to the intensive care unit.

The data submitted for approval already showed that there were virtually no severe courses in the vaccine groups of all three manufacturers. In the meantime, however, more information is available. Scientists working with Eleftheria Vasileiou from the University of Edinburgh, for example, examined the data from 5.4 million Scots. They wanted to know how well the first of the two corona vaccinations already protects against hospital admissions for Covid-19. In a study recently published by the specialist magazine Lancet, they now report that the Biontech vaccine can reduce the number of hospital stays by 85 percent after the first vaccination, and that of Astrazeneca by as much as 94 percent. For people aged 80 and over, the combined risk of both vaccines was 81 percent.

All sorts of interesting findings are to be expected, especially about the Astrazeneca vaccine, which is apparently somewhat frowned upon in this country. Because there are indications, for example, that its effect increases significantly in the twelve weeks after the first vaccination. This effect did not even come into play in the approval studies. The immunologist Christine Falk from the Medical University of Hanover expects that the effectiveness for the older age groups will soon be well proven, as can already be seen from the current evaluation of the vaccinated in Scotland. And it refers to the already well-documented safety and tolerability of the Astrazeneca vaccine. “At the moment, vaccination reactions such as fever, chills and fatigue are often discussed. These can be relatively strong, especially in younger people, but are not a cause for concern. Because they simply show that the immune system is reacting and building up the desired protection, ”says the professor.

Conclusion: In the current situation, the following applies in any case: Even a vaccine with 60 percent effectiveness is a great benefit in the fight against the pandemic - for each individual, but also socially.

The corona check topics at a glance