And another 815 students were told Wednesday they face suspensions of up to 20 days if their parents don't provide the documents, which Ottawa Public Health has been requesting for six months.
"When people don't act, you have to have some kind of stick there to say, 'Hey, you're at the last stage. We need this, this is provincial law,'" said Eric Leclair, head of health information co-ordination with Ottawa Public Health.
At the beginning of the school year, 53,000 Ottawa high school students had their immunization records assessed, part of an annual review required by a provincial law on the books since 1982.
Roughly 5,500 students received a third warning at the end of March, with a suspension notice if they did not comply.
The letters were sent out earlier than usual this year so the suspensions would not coincide with end-of-term exams, Leclair said.
Students can be exempted from receiving the six required vaccines for medical, religious or philosophical reasons.
Leclair said about two per cent of students receive exemptions, but he stressed the importance of immunization.
"Immunization is the public health tool that is the most effective next to clean water and sanitation," Leclair said.
"Vaccination is the No. 1 way to keep people disease-free."
Leclair said the province is slowly moving toward a more streamlined system to keep track of immunization records.
"There is a lot of talk about having a centralized system where physicians would submit the proof of vaccination to a centralized system, and then we'd access that database," Leclair said.
"We wouldn't have to go through this exchange with parents."
Suspended students can return to school as soon as they have received their shots and updated documents are submitted.