a call to someone to participate in a competitive situation or fight to decide who is superior in terms of ability or strength

he accepted the challenge

a call to prove or justify something

a challenge to the legality of the banning order

the administration of an immunogenic or infectious agent to an animal or person, in order to study the resulting immune response or measure the efficacy of a vaccine

challenge trials have yielded positive results when carefully and ethically conducted

human challenge studies occur in tightly controlled settings

recently vaccinated calves should be protected from challenge

invite (someone) to engage in a contest

he challenged one of my men to a duel

organizations challenged the government in by-elections

dispute the truth or validity of

it is possible to challenge the report's assumptions

administer an immunogenic or infectious agent to an animal or person, in order to study the resulting immune response or measure the efficacy of a vaccine

the mice were challenged with the influenza virus