95 percent effectiveness, 80 percent effectiveness – or only 70 percent effectiveness? The data on the newly developed Corona vaccines first make many people aware that vaccinations vary in effectiveness – and that no vaccination offers 100 percent protection.
Already, the first people would rather not be vaccinated with the “less effective” vaccines from AstraZeneca or Johnson & Johnson. But is the difference really as great as the figures suggest?
Effectiveness against disease
To test the efficacy of a vaccine, large Phase III trials compare how many participants get sick without the vaccine and how many get sick despite it.
If a pre-specified number of participants have become ill, this double blinding is removed. In this case, the diseased include all participants who developed symptoms, even if it was only a transient cough. If the proportion of vaccinated among the infected is lower than that of the unvaccinated, the vaccine is effective.
The efficacy data thus refer to a relative reduction in risk. They show how much lower the risk of disease is for vaccinated people compared with people who are not vaccinated. However, they do not reflect how high the overall risk of disease is for both groups. This is because it depends on many other factors, such as how much the virus is currently spreading (incidence) or how vulnerable each person is.
Complete protection against severe courses
The decisive factor, however, is how reliably the vaccines prevent severe courses of the disease. And this protection was extremely high in the course of the studies with all approved vaccines: no vaccinated participant in the studies became seriously ill with covid-19 – this applies both to the mRNA-vaccinated subjects and to those who had received a vector vaccine.
Efficacy against infection
Another form of efficacy describes how well a vaccine protects not only against the outbreak of a disease but also against infection. Doctors refer to this as “sterile immunity”. If this is guaranteed, it means that a vaccinated person cannot infect anyone else.
Based on current knowledge, corona vaccines cannot completely prevent re-infection, but the likelihood of passing on the virus appears to be significantly reduced even in such cases.
Efficacy against mutants
For this reason, adults and older children are much less likely to contract influenza than younger children. This is because they have already come into frequent contact with flu viruses in the course of their lives. Their immune memory therefore also reacts to new flu viruses, albeit less so than to “old acquaintances”.
However, the currently available vaccines do indeed seem to have lost some of their efficacy.
But this does not mean that the vaccines have no protective effect at all against the mutants. For example, they can still at least prevent severe disease progression. However, the extent to which this is actually the case and how well the vaccines work against the various mutations remains to be seen.
No 100 percent protection against disease and death
This is particularly true for older people, who still make up the largest proportion of those vaccinated: Their immune systems are less powerful than those of younger people, which is why their immune response can be lower. At the same time, they are the ones who have the highest risk of dying from an infection.
