THESSALONIKI, Greece (AP) — Fighter jets flew over the northern Greek city of Thessaloniki in an aerial display Thursday as troops marched in the city’s center below to mark Greece’s national holiday commemorating the country’s formal entry into World War II.

But some student parades traditionally held in municipalities across the country were cancelled, especially in parts of northern Greece which have seen a spike in coronavirus infections, fueled by low vaccination rates in those areas.

Greece’s Oct. 28 national holiday, known as Ochi Day, or No Day, marks the day in 1940 when Athens rejected an ultimatum by Fascist Italy to allow Axis forces to enter Greek territory and take control of parts of it. The refusal led to an invasion by Italian troops hours later, marking the country’s entry into the war.

Parades last year were cancelled as the country grappled with the coronavirus pandemic. This year, most were allowed to go ahead, although Thessaloniki’s military parade was somewhat pared down, with only military, fire and security forces parading without the participation of many of the civic groups and associations that traditionally take part. Participants and spectators alike were asked to wear masks.

But several municipalities and regions across northern Greece cancelled parades by schoolchildren amid spiking coronavirus cases.

Just over 61% of Greece’s population of around 11 million has been fully vaccinated, and only slightly more — just under 64% — has received at least one dose. The country has been seeing increasing coronavirus infections, particularly in parts of northern Greece, with intensive care units beginning to fill up.

New cases are around 2,000 to over 3,000 per day, with dozens of deaths and ICUs set aside for COVID-19 patients in the country are now at 77% capacity. On Wednesday, Greece reported 63 deaths and 3,651 new coronavirus cases, bringing the total death toll to 15,770 since the start of the pandemic, with 728,210 confirmed cases.