Yep, they're definitely accidents, by definition.
accident
1
a
: an unforeseen and unplanned event or circumstance
Their meeting was an accident.
b
: lack of intention or necessity
: CHANCE
They met by accident rather than by design.
2
a
: an unfortunate event resulting especially from carelessness or ignorance
was involved in a traffic accident
b
medical
: an unexpected and medically important bodily event especially when injurious
a cerebrovascular accident
c
law
: an unexpected happening causing loss or injury which is not due to any fault or misconduct on the part of the person injured but for which legal relief may be sought
d
US, informal
—used euphemistically to refer to an uncontrolled or involuntary act or instance of urination or defecation (as by a baby or a pet)
an unforeseen and unplanned event or circumstance; lack of intention or necessity : chance; an unfortunate event resulting especially from carelessness or ignorance… See the full definition
www.merriam-webster.com
Using a condom and having it break is an unforeseen and unplanned event or circumstance.
Using birth control pills and having a vasectomy and still getting pregnant is an unforeseen and unplanned event or circumstance.
Taking birth control pills without knowing that antihistamines can interfere with their effectiveness is an unforeseen and unplanned event or circumstance.