With chatter about a potential seventh wave of COVID-19 cresting in Ontario, the province's chief medical officer of health has called a press conference to address eligibility requirements for fourth doses (read: booster shots) of vaccines against the virus.

Ontario's Ministry of Health announced late Tuesday afternoon that Dr. Kieran Moore "will provide an update on the province's rapid antigen test program and expanding access to fourth doses of COVID-19 vaccines."

Moore is scheduled to make remarks at 11:00 a.m. tomorrow, Wednesday, July 13, from the Ontario Legislative Building's media studio.

As it stands currently, the only Ontarians eligible for a fourth shot (or second booster post) are those who are aged 60 or older, and people over 18 who are First Nation, Inuit and Métis individuals, as well as non-Indigenous household members.

Others eligible for fourth or even fifth doses depending on their circumstances and timing of last shot include long-term care home residents, retirement home residents, elder care lodge residents and older adults living in other congregate settings that provide assisted-living and health services.

Ontario has come under increasing pressure in recent weeks to expand eligibility for fourth doses to all adults amid rising case counts, with doctors and public health experts aligned on what needs to happen.

Dr. Moore himself stated during an interview with The Canadian Press last week that Ontario was considering allowing people under 60 to recieve their fourth doses of a COVID-19 vaccine. At the time, he noted that he was uncertain as to the "when" and "how" this will happen.

He did make clear, however, that he is more concerned about people who haven't recieved even a first booster shot (some five million in his estimation) than healthy people awaiting a fourth.

"Of those five million that haven't had even [had] their first booster, many of whom it's well after six months since their last dose, one million of them are over 50 years of age, and we know age is a really significant risk factor for COVID, severe outcomes and hospitalization," said Moore on Thursday, July 7.

"So we're asking first, before we open up any further, that... all five million... who haven't come forward, please consider getting vaccinated in the month of July."

While firm restrictions are in place regarding how long after a first dose someone can get another, there are plenty of exceptions to the general "under 60" rule listed on the province's website.

Transplant recipients, some cancer patients, people with HIV or another immunodeficiency syndrome, and people undergoing treatments with specific immunosuppressive medications may qualify differently.

"Dose numbers for booster doses may vary depending on an individual's primary series or specific circumstance. The majority of Ontarians received a two-dose primary series (Moderna, Pfizer and/or AstraZeneca), so their first booster (Moderna or Pfizer) would be considered their third dose, and a second booster would be considered their fourth dose," reads the site.

"Individuals who are moderately to severely immunocompromised are eligible for a three-dose primary series, so their first booster would be considered their fourth dose, and their second booster would be considered their fifth dose."