In the northern hemisphere, winter is approaching and people are beginning to associate the arrival of cold weather (November to April) with multiple viruses. In this sense, the public health expert, Alejandro Macías Hernández, explained that three viruses are circulating at the same time: the respiratory syncytial virus (RSV), influenza, or seasonal flu virus, and the coronavirus or catarrhal viruses.

He warned that with the pandemic produced by the SARS-CoV-2 coronavirus, these viruses lost their seasonality. However, to the extent that we are coming out of the peaks, particularly the peak of the Delta COVID-19, "it is very likely that they will pick it up again".

He pointed out that the respiratory syncytial virus (RSV) affects mainly children with bronchitis that can be serious and detailed that in November the peak of this disease begins to rise, reaches a maximum in January, and drops to end towards the end of March or beginning of April.

Influenza or seasonal flu is very common and infectious, it affects older adults, young children, and people with chronic health problems with serious complications. "Influenza generally begins to rise in early December, peaks in late January, February and ends around the end of April now to go down to minimum levels."

"At the same time, but entering already towards the end of December generally come the coronaviruses that traditionally were considered as catarrhal viruses."

What happened during the influenza seasons 2019-2020 and 2020-2021?

Macías Hernández, a graduate of the UNAM postgraduate program, recalled that in China COVID-19 started in December 2019 and consequently the end of the 2019-2020 influenza season disappeared due to the entry of the coronavirus. The 2020-2021 influenza season also disappeared from the northern and southern hemispheres of the planet, "it was practically subjugated by the coronavirus".

According to his calculations, the SARS-CoV-2 coronavirus may become seasonal and circulate at the same time as catarrhal coronaviruses and influenza, which could lead to health complications for the population.

"As long as there is the circulation of respiratory viruses, we will have to continue using masks, we will have to continue avoiding crowds of people, we will have to continue ventilating closed spaces, and, very importantly, we will have to get vaccinated against influenza", he advised.