An adverse event is any medical event that occurs after vaccination. Usually it is impossible to know if any individual event is related to vaccination, so reporting systems (like VAERS) are used to aggregate this data so it can be examined statistically. Experts can use this data to identify potential safety signals (events that seem to be occurring more often with vaccination than you might expect otherwise). Once a safety signal is identified, separate research is done to determine if there is a potential causal association.
There are currently only 4 serious adverse events that are associated with COVID-19 vaccines according to the CDC. These could be considered "known side-effects".
Only 2 of these 4 apply to mRNA vaccines: Myocarditis/Pericarditis and Anaphylaxis (alergic reaction). The latter occurs at a rate of about 5 cases per million doses. The former is described on another page.
One additional potential side-effect (ischemic stroke in people ages 65 and older who received the bivalent Pfizer-BioNTech COVID-19 Vaccine) is under investigation (as of 2023-01-22).
Based on current information, any other adverse events (for example, those reported to VAERS and similar reporting systems), should be considered most likely UNRELATED to vaccination. The CDC will continue to monitor for safety signals and will conduct investigations as appropriate whenever a potential association is detected.
Information about serious adverse events associated with Covid-19 vaccination:
Source of claim: Pfizer document 5.3.6 Cumulative analysis of post-authorization Adverse Event Reports of PF-07302048 (BNT162B2) Received Through 28-FEB-2021, Appendex 1: List of Adverse Events of Special Interest
AESI are not side effects. AESI lists are developed by trial sponsors BEFORE a clinical trial is undertaken and lists events that should be reported by the investigator to the sponsor IF they occur.
The list includes items such as "Product availability issue", "Product distribution issue", "Product supply issue".
The list includes items such as "SARS-CoV-1 test", "SARS-CoV-1 test negative", "SARS-CoV-1 test positive", "SARS-CoV-1 antibody test", "SARS-CoV-1 antibody test negative", "SARS-CoV-1 antibody test positive", "SARS-CoV-1 carrier"...
Definition of Adverse Events of Special Interest:
"An adverse event of special interest (serious or non-serious) is one of scientific and medical concern specific to the sponsor’s product or programme, for which ongoing monitoring and rapid communication by the investigator to the sponsor may be appropriate."
Related: Pfizer Documents