Jonathan Spector’s 2018 comedy “Eureka Day” first attracted attention in productions in Berkeley and Brooklyn. But in its sharp U.K. premiere starring Helen Hunt, this often very funny satire about parental attitudes to an outbreak of mumps has suddenly leapt into focus — since it’s really about fiercely personal, highly politicized responses to enforced vaccination. This depiction of over-articulate parents fighting it out in initially polite then savage dialogue (now playing at the Old Vic in London) owes a huge debt to Yasmina Reza’s more caustic “The God of Carnage,” but anyone searching for proof that timing is everything need...