http://www.sciencemag.org/news/2020/12/suspicions-grow-nanoparticles-pfizer-s-covid-19-vaccine-trigger-rare-allergic-reactions

Some people suspect polyethylene glycol may have triggered severe reactions in at least eight people who received the Pfizer-BioNTech vaccine in the past 2 weeks.

Science’s COVID-19 reporting is supported by the Pulitzer Center and the Heising-Simons Foundation.