BRISBANE, Australia—Novak Djokovic will get a chance to defend his Australian Open title after receiving a medical exemption to travel to Melbourne, ending months of uncertainty about his participation because of the strict COVID-19 vaccination requirements in place for the tournament. The top-ranked Djokovic wrote on Instagram on Tuesday he has “an exemption permission.” Djokovic, who is seeking a record 21st Grand Slam singles title, has continually refused to reveal if he is vaccinated against the coronavirus. The Victoria state government has mandated that all players, staff and fans attending the Australian Open must be fully vaccinated unless there is a genuine reason why an exemption should be granted. Australian Open organizers issued a statement later Tuesday to confirm Djokovic will be allowed to compete at the tournament, which starts on Jan. 17, and is on his way to Australia. He earlier withdrew from Serbia’s team for the ATP Cup, …