A public health unit in southwestern Ontario said its COVID-19 vaccine booking website was recently hit by bots that tried to scoop up appointments for some users while blocking others from using the system.

The Middlesex-London Health Unit said the incident was similar to what happens when scalpers use automated programs to buy up large quantities of concert tickets on sites like Ticketmaster.

The health unit's top doctor said the bot attack took place on Monday and allowed some people to bypass certain steps in the booking process while stopping others from securing slots.

"What we think was happening was that some people were doing everything possible to make sure that their loved ones could get a spot in the vaccine queue," Dr. Chris Mackie said in an interview Tuesday.

Mackie said Verto Health, the company that owns the booking system, informed the health unit of irregular activities on the website and has since adjusted the system to guard against such incidents.

No one was able to book multiple appointments as a result of the bot incident because Ontario health card numbers are required to schedule shots, Mackie said.

Mackie added that he also didn't believe anyone was trying to book slots using the bots in order to sell them to others.

He said the health unit's booking site, which is different from the province's booking portal, has otherwise been running smoothly since it launched.

"We ran the exact same program three weeks ago when we opened for everyone 80 and above, and we booked over 5,000 appointments within about an hour," he said.

Mackie's health unit launched its own booking portal before the provincial system went live and has continued to use the local site since.

The Middlesex-London health unit is currently offering COVID-19 vaccine appointments to residents aged 75 and older.

The province's online vaccine booking system launched last week.

This report by The Canadian Press was first published March 23, 2021.

This story was produced with the financial assistance of the Facebook and Canadian Press News Fellowship.