BARRIE, ONT. -- One of the region's top doctors is saying while he's optimistic by recent COVID-19 data, he's urging caution with a highly contagious variant gaining steam.

Dr. Colin Lee, the associate medical officer of health for the Simcoe Muskoka District Health Unit (SMDHU), says that he is encouraged by the recent downward trend of cases. However, he remains very concerned over the increasing circulation of the Delta variant.

Lee says that the B.1.617 variant, which was recently dubbed Delta by the World Health Organization, could soon overtake the current dominant B.1.1.7 variant.

"The current evidence also indicates that the vaccine effectiveness is about 50 per cent less for those that have only had one dose," Lee said to CTV News. "But the vaccine effectiveness is excellent if you've had two doses."

Lee says with this more transmissible variant posing a threat that it's crucial to vaccinate as much of the population with both required doses as soon as possible. He says there are approximately 28,000 appointments set for next week.

As of Thursday, about 66 per cent of the eligible population in Simcoe Muskoka has received their first dose of a COVID-19 vaccine, while only about 42,000 people have received their second dose.

"What I understand from the province is that they are really going to try to accelerate second doses as the vaccine supply is looking very, very promising for the rest of June and July," says Lee.

As of Friday, those who received the AstraZeneca vaccine for their first dose can choose to continue with that for their second dose, or they can opt to receive a dose of the Pfizer or Moderna vaccine.

Lee says this is great news, providing more options to get more vaccines out as quickly as possible. He does note that those who do choose to receive a different dose many notice more severe side effects but that it remains safe. He also says the risk of blood clots is less with the second dose of AstraZeneca.

"Both are good options," says Lee. "Both choices are good. It's just a matter of what certainties and uncertainties you are willing to accept."

When it comes to the province's decision to keep schools closed to in-person learning until September, Lee says he was saddened and left confused by the premier's call to hold outdoor graduation ceremonies for all grades to make up for the lost time in the classroom.

"The announcement from Premier Ford, to be honest, came as a big surprise to us and also to school boards," Lee says.

The region's second-top doc says that the health unit will work to support plans where it can, but it is still recommending schools stick with a virtual celebration. Assuming the province will enter Step One of its reopening plan by the time ceremonies are held, outdoor gathering limits would be capped at no more than 10 people.

Lee says they are awaiting further guidance from the province as it may amend the guidance to accommodate the outdoor ceremonies.

"We are certainly more in favour of the remote option," Lee says. "Having said that, we are awaiting the provincial guidance or more details on that. But under the framework right now, we are not really supportive of gatherings of more than 10 people."