At Sidaction on March 27, 2021, Jean-François Delfraissy, President of the Covid-19 Scientific Council, said, “Covid-19 has been an ‘unprecedented crisis,’ unmatched to HIV or Ebola.” This claim deserves to be discussed. The reflection is based on a comparison, articulated in three sequences : emergences, circumstances, consequences.AIDS and Covid-19 are two viral diseases but are very different and unequally transmissible. Both have broken records : the triggering of the global alert, the identification of infectious agents, the global spread, the mobilization of scientists, the dissemination of information, all dynamics whose modalities are symptomatic of their respective times. Both are facing difficulties in implementing preventive measures, unequal access to treatment or vaccines. Both are observatories of lifestyles, levels of global connectivity. Systemic destabilizers, both accentuate socio-economic disparities at the expense of the most vulnerable. These pandemic diseases share, beyond their specificities, points specific to health earthquakes in the history of humanity.