A Catalan study of 30,000 PCR samples found Covid peaks in August and September. The pattern has reopened the debate over autumn vaccination timing, but researchers say more evidence is needed.
For three straight years, Covid outbreaks in Catalonia have reached their highest point in August or September. A study of 30,000 PCR samples found the pattern as respiratory infections crossed the epidemic threshold again, while Covid positivity reached 27.2%.
That raises a practical question. Should vaccination start before the current window of mid-September to mid-October? Spain's autonomous communities generally offer Covid and influenza protection during that period. Researchers have raised the issue, but they have not said the autumn campaign should move.
Catalonia’s SIVIC surveillance system monitors SARS-CoV-2 in real time alongside influenza, RSV and other respiratory pathogens, providing the regional data used to track changing seasonal patterns.
Aida Perramon-Malavez led the study. She works with the Primary Care Information System at the Catalan Institute of Health, or ICS. The paper appeared in Eurosurveillance, the journal of the European Centre for Disease Prevention and Control.
The research team tracked 18 respiratory viruses in Catalonia from 2022 to 2025. Independent reporting on the same regional surveillance work describes an analysis of more than 33,000 samples. Some viruses stayed active at low levels throughout the year. Others formed clearer waves between late autumn and early winter.
The regional setting has also included other alerts, such as an earlier Catalan warning. This study used laboratory surveillance, not weather monitoring.
At first, SARS-CoV-2 appeared to follow influenza's winter pattern. Then the timing changed. In each of the next three years, outbreaks began in spring, peaked in August or September and fell toward the start of winter.
Researchers have seen a similar shift in places including the United Kingdom. Catalonia is following that direction this season.
That matters.
Catalonia began its combined influenza and Covid vaccination campaign on 5 October 2026, while expansion to additional groups was scheduled for 26 October. The regional timetable therefore remains autumn-based even as surveillance points to repeated late-summer Covid peaks.
National surveillance shows how quickly the latest rise appeared. The Acute Respiratory Infection Surveillance System of the National Centre for Epidemiology recorded no Covid wave in 2026 until the start of September.
The surge came during the last two weeks. Respiratory infections reached 478.2 cases per 100,000 inhabitants, the first time they had passed the epidemic threshold since last winter.
Covid is driving the increase. Its positivity rate has risen to 27.2%, although the overall intensity of respiratory disease remains low.
Jacobo Mendioroz, deputy director general for Public Health Surveillance and Emergency Response at the Generalitat of Catalonia and a co-author of the study, said there is no clear explanation for the seasonal shift. One possibility is that the virus now appears during a period with less competition from other respiratory viruses. Researchers do not consider the winter pattern definitively over.
If the pattern continues, public health authorities may need to review the timing and reach of vaccination campaigns. They may also need to assess the value of combined vaccines.
Mendioroz still considers October vaccination reasonable. He says one study cannot justify a change. More surveillance is needed.
The Catalan programme targets people at higher risk rather than the entire population. The groups include older adults, residents of long-term care facilities, pregnant people, young children, healthcare workers and people with chronic conditions.
During the 2025–2026 campaign, Catalonia administered 1,524,442 influenza vaccine doses and 934,309 Covid doses. Regional health data put influenza coverage among recommended groups at 39.6%.
Those figures show why timing matters. Health authorities need to reach people before respiratory-virus activity rises.
Fernando Moraga-Llop, a paediatrician and spokesperson for the Spanish Association of Vaccinology, has also warned that changing the schedule would be difficult. Splitting Covid vaccination into two periods could weaken the campaign because of logistics and public acceptance.
For now, the study calls for a review rather than an immediate change. It does not cancel the autumn campaign. It also does not prove that Covid has become a summer disease.
What it shows is narrower. Covid produced a repeated late-summer pattern across three years, and that pattern now affects a live vaccination decision in Spain.
The sensible course is to keep the October timetable while checking whether the August and September peaks continue. Moving the campaign before the evidence is stronger would be premature. Ignoring the shift would be difficult to justify.
