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Goodbye Flu, Hello Spring and Summer Viruses: What’s Coming Next?

As Canadians wave goodbye to the seasonal discomforts of respiratory viruses, like the flu, a new question arises: what other microscopic troublemakers will emerge with the warming weather?

As winter gives way to spring and outdoor gatherings become more common, experts stress the importance of staying alert to a variety of viruses that thrive in the warmer months. While some contagious bugs, such as the common cold and flu, may fade as temperatures rise, others persist throughout the year or even become more active.

Reflecting on the recent flu season, Dr. Colin Furness, an infection control epidemiologist and assistant professor at the University of Toronto’s faculty of information, describes it as relatively “moderate.”

“It peaked in the middle of winter, with influenza A nearly gone and influenza B peaking recently, albeit a bit later, but also on the decline,” Furness explained to Global News.

He noted that by the end of April, flu activity could typically be substantial, but this year is an exception.

Recent data from the Public Health Agency of Canada’s (PHAC) Flu Watch indicates a steady decrease in national flu activity over the past few weeks. Influenza A cases continue to decline and are lower than those of influenza B, which is also decreasing, according to PHAC.

With influenza season winding down, Canadians can expect the emergence of various other viruses and bacteria as the warmer months approach. Get ready for a shift in microbial dynamics as temperatures rise.


Enteroviruses, a diverse group of viruses numbering over 100 types, are more prevalent during summer. They cause a range of illnesses, from mild cold-like symptoms to severe respiratory and neurological conditions, as per the BC Centre for Disease Control. While most infections are asymptomatic, infants and children are more vulnerable due to lack of previous exposure and immunity.

Dr. Gerald Evans from Queen’s University notes that enteroviruses proliferate in water, making waterborne transmission common in summer when people engage in water-related activities. Polio, once feared during summer before vaccination, serves as a classic example.

Hand, foot, and mouth disease, prevalent in summer, particularly affects children, causing painful blisters. Additionally, rhinovirus, responsible for the common cold, can still occur during warmer months, albeit less commonly than in spring.


Despite a spike in COVID-19 cases alongside other respiratory illnesses like influenza during winter, a clear seasonal pattern for COVID-19 has yet to emerge. Dr. Furness suggests that unlike influenza or rhinovirus, COVID-19 doesn’t depend on specific conditions for spread, making it more akin to measles in terms of contagion.

Current COVID-19 cases in Canada remain low, as per national wastewater surveillance. Dr. Furness emphasizes that due to its high contagion rate, COVID-19 doesn’t follow seasonal trends, posing a continued risk during spring and summer. He advises being prepared for possible exposure, especially in crowded places, where the virus may be more infectious.


Norovirus, also known as the stomach flu or winter vomiting bug, is a highly contagious virus causing acute gastroenteritis. It spreads primarily through contaminated food, water, surfaces, or direct contact with infected individuals. Once ingested, it targets the stomach and intestines, leading to symptoms like nausea, vomiting, diarrhea, and stomach cramps. Dr. Furness notes that norovirus thrives in warmer weather, making it more prevalent during milder seasons. It poses a particular risk for travelers, especially in areas with varying hygiene standards or crowded settings like cruise ships, which are often associated with norovirus outbreaks due to close quarters and communal dining areas.


Arboviruses, or arthropod-borne viruses, are a diverse group transmitted by mosquitoes, ticks, or sandflies. Dr. Evans notes the resurgence of West Nile virus, carried by mosquitoes, typically in mid-to-late summer. While some infected individuals may not show symptoms, others may experience flu-like symptoms such as fever and fatigue. Although more common in Western Canada, periodic outbreaks occur in Ontario.

West Nile virus, not native to North America, arrived in the late 1990s and is now established across Canada. It usually causes mild febrile illnesses. Another summer arbovirus is Powassan virus, transmitted by ticks, particularly the black-legged tick. Named after Powassan, Ontario, it’s rare, with only one or two cases reported annually in Ontario, often associated with groundhog hosts.

How to stay safe

As summer brings forth new viruses, Evans and Furness stress the importance of basic handwashing as the best defense. Evans highlights the significance of hand hygiene in preventing the transmission of various illnesses. Furness recommends carrying hand sanitizer when outdoors to effectively ward off viruses, especially for families with young children. He emphasizes the affordability and effectiveness of this simple practice.

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