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Seasonal coronaviruses such as OC43 in general cause mild common cold or upper respiratory
symptoms, although some patients may develop pneumonia6. Our patients symptoms were severe
enough to require hospital admission for respiratory insufficiency. We are intrigued by the fact that
past COVID-19 and recent vaccination did not seem to provide any protective effect in this case
against coronavirus OC43. There is growing evidence that the clinical manifestations of respiratory
viruses are related to immune interfering mechanisms, which can be particularly important for
epidemic and pandemic coronaviruses7. While current studies have focused on the potential effect
of past coronaviruses over SARS-COV2 infection, to our knowledge there has been no investigation
on the reverse situation, that is, if SARS-COV2 can have an impact on the incidence or severity of
other coronaviruses. The role of antibody-dependent enhancement in human coronaviruses, and for
SARS-COV2 in particular, has yet to be established8. Further studies and epidemiological surveillance
will help to determine if our case is just an oddity or if the current pandemic may yet have other
unexpected collateral effects.