GUELPH -- Wellington-Dufferin-Guelph Public Health is tightening its COVID-19 self-isolation policy, now requiring all non-vaccinated members of a high-risk contact's household to also stay home and isolate.

The update, announced Tuesday and immediately put into effect, requires "unvaccinated members of a household where someone has had a high-risk exposure" to not attend school or child care and to only leave the home for essential reasons including attending work or picking up groceries and prescriptions.

"By expanding who is required to self-isolate, we can reduce transmission in schools, workplaces and other venues, and end small outbreaks before they become large ones," Dr. Matthew Tenenbaum, associate medical officer of health, said in an emailed statement.

The health unit said unvaccinated household members can return to school and other activities only once their isolation period ends.

The decision to amend the isolation policy was driven by the high transmissibility of the Delta variant, officials said.

"We’re seeing some concerning trends here in the fourth wave. We know the Delta variant is more transmissible, but we’re also seeing a much shorter time for symptoms to arise,” Dr. Tenenbaum said. “That means cases can arrive and spread faster than the case management process can always contain – even when it’s working at its most efficient. This is something we have seen in some school cases this fall."

High-risk contacts who are fully vaccinated are not required to isolate as long as they are symptom-free. Fully vaccinated members of a high-risk contact's household are also not required to stay home.

With files from CTV Kitchener's Krista Sharpe.