New ‘atlas’ of respiratory infections suggests Covid is no longer just a winter virus

A comprehensive atlas of the 18 main respiratory viruses circulating in Catalonia, produced for the first time in Spain by researchers from that northeastern region, reveals that the coronavirus that caused the Covid-16 pandemic — SARS-CoV-2 — “is currently not a winter virus. In recent years, it has shown clear peaks during the spring and summer, which is different from what was initially expected.”

This behavior has caused a clear mismatch with the current vaccination calendar. “We are immunizing at-risk groups [older people, those with chronic illnesses...] in the autumn, when the virus’ epidemic waves have already passed, and not beforehand, as would be desirable. This work raises the possibility that it may be necessary to adjust the planning of vaccination campaigns and guidelines,” warns Jacobo Mendioroz, deputy director general for Surveillance and Public Health of the Catalan government.

The research’s findings, based on Catalonia’s healthcare system data between 2022 and 2025, have been observed this year again in the real world. Coronavirus incidence surged at the end of summer, when communities had not yet begun the vaccination campaign against this pathogen, which is administered alongside the flu shot.

The new research highlights SARS-CoV-2’s behavior, more erratic after the pandemic but now showing mainly “a clear summer epidemic pattern.”

Juan Carlos Galán, head of Virology at Ramón y Cajal Hospital in Madrid, considers the research highly relevant but says it is still too early to classify the coronavirus as exclusively a summer virus: “There are recent data from other European countries, and some areas of Spain, that point more to a biennial incidence, in summer and winter. What was observed in Catalonia over these three seasons indicates a trend in SARS-CoV-2 behavior, but we do not know whether other viral or environmental factors could have impacted that finding and we will have to wait for the next seasons to confirm it.”

This expert highlights the study’s contribution to a “fascinating field” he calls viral ecology. “We see that there are interferences and, at times, what appears to be competition among different viruses. A good example was the first year of the pandemic, when influenza disappeared completely, overwhelmed by covid. This apparent antagonism between flu and SARS-CoV-2 is observed in subsequent years. Each virus unfolds on the calendar in an orderly way, as if occupying different niches. Many factors intervene in this process, even if they are not fully understood,” he concludes.

Changing vaccination campaigns

For Gregorio Montes Salas, secretary general of the Spanish Society of Preventive Medicine, Public Health and Healthcare Management (SEMPSPGS), the study confirms that “the coronavirus has not followed the expected winter pattern, at least so far.” He adds that this raises the option of “considering the possibility of de-seasonalizing vaccination against SARS-CoV-2.”

Mendioroz and Montes Salas agree that before making decisions “it will be necessary to wait for further research,” given the logistical complexity of changing campaigns and the risk of undermining achieved coverage (65% for flu among those 65 and older and 50% for coronavirus).

The underlying idea is that, even if belated, it is preferable for at-risk people to be immunized by taking advantage of the momentum of regional autumn campaigns rather than spreading doses across the year and losing adherence. “Campaigns make mass vaccination easier. Changing dates requires a logistical effort that must be carefully studied, but it may be something worth exploring,” Montes Salas says. “The whole organization, the messaging and even public perception would change. The risk is that coverage could drop: who is going to get vaccinated at the start of summer against a virus that has always been associated with cold weather?” adds Mendioroz.

The paper was published in the latest issue of Eurosurveillance — the scientific journal of the European Centre for Disease Prevention and Control (ECDC) — and its main aim was to obtain a detailed picture of respiratory virus circulation. “Influenza has always been monitored and, more recently, Covid and respiratory syncytial virus (RSV). But what about the others? The answer provides key information: it helps plan prevention measures, prepare health centers or hospitals for peaks in demand and even anticipate what might happen,” Mendioroz says.

One reason this is possible, the study’s conclusions argue, is that “respiratory viruses mainly follow a predictable pattern, appearing one after another in a consistent order every year.” “We know, for example, that the flu wave is successively preceded by a rhinovirus wave and then a parainfluenza wave,” the Generalitat’s deputy director general for Surveillance illustrates.

The researchers analyzed more than 33,000 samples obtained between October 2022 and September 2025 by the Information System for Infection Surveillance in Catalonia (SIVIC), the sentinel network that monitors respiratory viruses in real time. The panel tracks the following viruses and subtypes: three influenza A strains and one B, two RSV strains, SARS-CoV-2, two seasonal coronaviruses (NL63 and OC43), four parainfluenza types, and one each of the following groups: rhinovirus, enterovirus, adenovirus, metapneumovirus and bocavirus.

Influenza A shows the clearest seasonal pattern, according to the paper. Its peak usually occurs in Spain between late December and early February, although most often it happens in the second half of January. “Meanwhile, influenza B displays a less regular seasonality” and is usually offset from that peak, the researchers conclude. RSV also has a clear winter pattern, although in this case it precedes the flu by a few weeks and typically “reaches its peak roughly a month before it.”

Rhinoviruses and enteroviruses, which cause mild cold-like illnesses, instead show a two-wave pattern, with peaks in autumn (September–October) and spring. Rhinovirus circulation also “declines when SARS-CoV-2 is circulating strongly,” the paper notes.

Another group of pathogens that infect the respiratory tract maintains a very different profile and shows a constant presence “throughout the year, without clearly defined epidemic peaks.” This is the case for adenoviruses, some coronaviruses other than SARS-CoV-2 (such as NL63) and two parainfluenza types (1 and 4).

The study also details the sequence of the remaining pathogens: parainfluenza virus 2 slightly precedes influenza, while metapneumovirus — a pathogen very common in childhood — and parainfluenza 3 emerge just as influenza begins to decline. Meanwhile, bocavirus and the seasonal coronavirus OC43 begin activity in mid-autumn, but their incidence rises slowly to reach peaks between February and April.

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