But there's a caution: while vaccine demand has been high, the next portion of the population could be harder to reach. The first part of an immunization program is always the easiest, said Scott Halperin, director of the Canadian Center for Vaccinology. "The latter parts where you're really trying to achieve those last few, that's harder, because you're trying to win hearts and minds of people who are much more doubtful, and we need to put in that energy in order to get that population," he said. Diners in the sky (Dmitri Lovetsky/The Associated Press) People have dinner sitting on a platform raised by a crane to a height of 50 metres and silhouetted against the sun as they participate in 'Dinner in the Sky' in St. Petersburg, Russia, on Wednesday.