The introduction of vaccine passports could backfire and stiffen opposition to vaccines among people who are already mistrustful, two medical experts told the Scottish Parliament on Thursday. Scotland’s vaccine passport scheme for nightclubs and large events officially begins at 5 a.m. on Oct. 1, though a grace period means that businesses will not face the threat of enforcement action until Oct. 18. Under the scheme, all adults, with a few exemptions, will have to prove they are fully vaccinated to enter nightclubs, sexual entertainment venues, indoors unseated live events with more than 500 audience members, outdoor unseated live events with more than 4,000 audience members, and other events with more than 10,000 audience members. Giving evidence to the legislature’s COVID-19 Recovery Committee, Professor John Drury of Sussex University described what he called the “backfire effect,” where anti-vaccine views stiffen. “Some groups harden, instead of becoming motivated to get vaccinated they …