aroch

First: The rate of thrombosis in AZ recipients is the less than it is in the general population -- Gen pop, ~.1% [1], AZ ~ 0.001% [2]. There is no evidence that the vaccine causes substantially higher risk. Also, the populations being prioritized for vaccination are a higher risk population for DVT to begin with.[1]

AZ, along with effectively every pharma company out there of note, takes the reporting of adverse drug responses (ADRs) very, very seriously. Both FDA and EMA require ALL companies that produce a labeled product (aka a drug you can "buy" and isn't only available in a trial setting) to investigate and report on every instance of a reported potential ADR. Companies want to investigate because they want to be able to keep selling their drugs. Regulators want to investigate because they want to limit ADRs as much as possible.

From the therapeutic point of view, it is bad if the treatment causes ADRs but also some may be unavoidable because of how the treatment works -- think chemo and cancer. The safety window for a drug is determined by balancing the therapeutic gain of treatment (usually, shorter time to recovery, increased QOL, or, in the case of cancers, increased life span/PFS) with the number and severity of known adverse effects. You might hear about cancer patients "cycling" their treatments, this is to allow time for the body to recover from known/expected ADRs.

Any way, this was a long winded way of saying every entity involved -- drug manufacturer, regulators, doctors, patients -- wants reports of ADRs investigated.