Recently, following the new certificate requirement, statements have been piling up on social media claiming that the greatest danger would come from vaccinated people, because thanks to the Covid certificate, they do not have to be tested before entering indoor spaces, and can still transmit SARS-CoV-2.
How do we respond to that statement?
First of all, it is true that people who have been vaccinated should also get tested in order to be even safer. In addition, people should continue to wear masks indoors, even if only vaccinated people are in the room. The reason is that the Delta variant is so contagious that aerosol researchers believe it would actually take that to get the disease under control.
Nevertheless, the statement above is only partially true. After all, it’s all about probabilities. An unvaccinated person is ten times more likely to be infected than a vaccinated person.
So out of 100 infected people who were exposed to the same risk of infection, only 10 are vaccinated.
Out of these people, only a portion is infectious, and the probability that a vaccinated person is infectious is significantly smaller than for an unvaccinated person. This is because the immune system of the vaccinated reduces the viral load more quickly than that of the unvaccinated. (Exceptions confirm the rule).
Rapid tests detect only 60% of those infected.
So out of the 90 tested and positive unvaccinated people, 54 are detected, but 36 still get through.
This means that the risk for the unvaccinated is still almost four times higher than that of the vaccinated.
PCR tests are much more reliable, but even with those, some remain undetected, and moreover, someone can become newly infected between sample extraction and certificate collection.
In other words, for every 100 infected people, there are certainly more unvaccinated than vaccinated individuals who pass the test. Thus, even if the vaccinated are not tested, the unvaccinated pose a greater risk – in terms of the probability of transmission – than the vaccinated.
Above all, however, this observation shows one thing: the matter is complex and depends very much on the combination of the various conditions. General statements such as “vaccinated people are dangerous” or “vaccinated people are not dangerous” lead to false conclusions. A differentiated view is still needed.