In 1989, McGeer joined the
Sinai Health System, where she specialised in microbiology. At the University of Toronto, she has focussed on developing mechanisms to stop the spread of infectious diseases in hospitals and care homes. McGeer has studied the impact of
influenza on hospital staff. She encouraged people of all ages to receive the
universal flu vaccine and supported hospitals in improving their influenza testing. She also contributed to a review of influenza diagnosis among older hospitalized patients on behalf of the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) Network. She is the director of infection control, and works as a microbiologist and infectious disease consultant at the
Mount Sinai Hospital. Her staff directory page acknowledges funding through an unrestricted educational grant from
Pfizer Canada. Her primary areas of research interest are the prevention of healthcare associated infection, the epidemiology of influenza, and adult immunization. She has received research grants from
Pfizer and
Seqirus, as well as personal and consulting fees from
AstraZeneca,
GlaxoSmithKline,
Janssen,
Medicago,
Merck,
Moderna, and
Sanofi Pasteur.
SARS and MERS McGeer led the investigations into
Severe Acute Respiratory Syndrome (SARS) in Toronto. She was based at the
Ontario SARS emergency operation centre. At the time, she contracted the disease, and accidentally exposed several other health officials to the disease. The health officials were quarantined and did not develop the disease. The
basic reproduction number of
severe acute respiratory syndrome-related coronavirus (SARS-CoV) was between 2.2 and 3.7, but
super-spreading events (highly efficient transmission of the virus) occurred in some hospital settings. McGeer believes that Toronto eliminated SARS by isolating people who were infected or at risk from the virus, preventing its spread. A study the critical care units of Toronto's hospitals found that the consistent use of
N95 masks was an effective way to protect nurses. During the 2013
MERS outbreak, McGeer visited
Saudi Arabia with the
World Health Organization to help to track the spread of the virus. Through careful monitoring of the air, food and water supply, McGeer helped to control the spread of the virus. including as a member of the
Ontario COVID-19 Science Advisory Table, the
COVID-19 Immunity Task Force leadership group, and the steering committee for Ontario's COVID-19 Genomics Rapid Response Coalition (ONCoV). She also serves on Canada's COVID-19 Expert Panel, assembled by Chief Science Advisor of Canada Dr.
Mona Nemer to assist in providing advice and guidance to
Prime Minister Justin Trudeau and the federal government. In late January 2020, McGeer expressed concerns over the ability to contain
SARS-CoV-2, particularly the unknown
incubation period, which makes it difficult to track and quarantine people who have been exposed. In early March she emphasized the need for Canadians to follow
public health advice to prevent the widespread transmission of SARS-CoV-2. According to McGeer, the most important guidance was to limit social contact and stay at home when feeling unwell. McGeer started to investigate how long SARS-CoV-2 can survive in air in March 2020. She was interested in how exhaled droplets, which contain both water and the virus, may become an infective aerosol that is light enough to be transported by air currents. In her role at Mount Sinai Hospital, McGeer acted as a local
principal investigator for the "CONvalescent Plasma for Hospitalized Adults With COVID-19 Respiratory Illness" (CONCOR-1) study. She also served as a principal investigator on a study examining the association between frailty and outcomes of
COVID-19 infection. In May 2021, McGeer explained that
National Advisory Committee on Immunization (NACI) deliberations over the use of
COVID-19 vaccines in Canada couldn't be made available to the public because the agency "has nothing like the budget or staff that would be needed" to do so. While NACI is mandated to "gather and evaluate the available data relevant to vaccines," McGeer also noted "they are not adequately resourced for rapid and comprehensive scientific assessment." She welcomed NACI's September 2021 recommendation of a COVID-19 vaccine booster shot for residents of long-term and congregate care facilities, citing evidence of waning immunity among this population. McGeer was recruited as a member of the newly formed Ontario Immunization Advisory Committee (OIAC), created by Chief Medical Officer of Health
Kieran Moore in August 2021 to work on provincial vaccine programs (including for
COVID-19). Beginning in August 2023, McGeer acted as an advisory panel member of the Review of the Federal Approach to Pandemic Science Advice and Research Coordination, tasked with conducting "a review of the federal approach to pandemic science advice and research coordination" for the
Government of Canada. The panel's report was published October 10, 2024. ==Membership==