The phenomenon of facilitating viral infections by antibodies exists for many viruses including coronaviruses. Instead of behaving as described by classical immunology (protective effect), antibodies allow the virus to penetrate target cells more easily. This mechanism could make a future vaccine against Covid-19 dangerous: this effect was demonstrated in animal tests with SARS1 vaccine candidates in 2003. This facilitation could also explain the second phase of the disease in severely affected patients: the acute inflammatory phase would be due to the facilitation by the high levels of anti-SARS-CoV-2 antibodies found exclusively in severely affected patients.
https://www.aimsib.org/en/2020/08/23/covid-graves-admettre-lexistence-des-anticorps-facilitateurs/