During the development of a vaccine to protect against the Sars-CoV-2 virus, it became apparent that the targeted agent could lead to false positive results in the usual tests for HIV1/2 antibodies. The project was subsequently terminated and the topic disappeared from the attention of science and the media. Thanks to access to anonymized patient data through our international network and case reports within our own reporting system for unusual events, we have come to the hypothesis that this "Australian effect" can also occur with other Sars-CoV-2 vaccines, albeit to a much lesser extent. In individual cases, however, this can have dramatic consequences. For this reason, we are publishing a hypothesis, contrary to our usual conventions. In no way do we wish to minimize the willingness to get vaccinated, nor do we wish to reproach any pharmaceutical company. Nevertheless, it is important to present the facts as they appear to us for discussion and to avoid adverse consequences should such an effect actually materialize in individual cases.