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Vol. 221. Issue 6.
Pages 372-374 (June - July 2021)
Vol. 221. Issue 6.
Pages 372-374 (June - July 2021)
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Global influenza surveillance in times of COVID-19: Robbing Peter to pay Paul?
Vigilancia internacional de la gripe en tiempos de COVID-19: ¿desvestir un santo para vestir a otro?
I. Sanz-Muñoza,
Corresponding author

Corresponding author.
, R. Ortiz-de-Lejarazu-Leonardoa, J.M. Eiros-Bouzaa,b,c
a Centro Nacional de Gripe, Hospital Clínico Universitario, Valladolid, Spain
b Servicio de Microbiología e Inmunología, Hospital Clínico Universitario, Valladolid, Spain
c Servicio de Microbiología, Hospital Universitario Río Hortega, Valladolid, Spain
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Dear Director,

The surveillance of influenza and other respiratory viruses is being relegated to the sidelines by the prominence of the COVID-19 pandemic. We were inspired to write this additional reflection on flu surveillance after reading a comparative study by Saint-Pierre et al.1 on the diagnostic activity of infectious respiratory diseases of viral etiology between 2019 and 2020 conducted in an institution in a country in the Southern Hemisphere.

The main mission of the 146 National Influenza Centres (NIC) of the World Health Organization’s (WHO) Global Influenza Surveillance and Response System (GISRS),2 which constitute the worldwide influenza surveillance network, is to identify and culture flu viruses from each region and geographical area so as to be able to design flu vaccines for the following season.

Given the current circumstances, the WHO has already expressed its concern about the COVID-19 pandemic blocking or hindering said surveillance and about efforts aimed at meeting the needs of SARS-CoV-2 influencing the effectiveness of future flu vaccines, hindering the ability to prevent a flu epidemic and pandemic surveillance.3

The Director-General of the WHO himself affirmed that the COVID-19 pandemic must not cause us to lose sight of other public health problems, including the flu. In that same document, the authors report that the number of shipments from the NICs to the WHO have declined by 62% and that there has been a 94% decrease in the number of flu virus genetic sequences uploaded to the Global initiative on sharing all influenza data (GISAID) platform.3

Nowadays, the official flu surveillance websites in Spain show less information than in previous seasons due to the effort needed to report cases and collect samples of SARS-CoV-2, which has displaced both the notification of flu cases and the collection of swabs in suspected cases. These requirements, along with cell culture, are necessary for obtaining flu virus strains that could be selected as candidates for the following year’s vaccine.

This is not about adding extra work on top of what Spanish hospitals are already bearing, but rather about underscoring the need to promote the NICs having a surveillance scheme that facilitates them meeting the stated objective. This would allow Spain to have flu strains available this upcoming season, even if there are fewer of them, thus meeting the objectives and standards of the WHO’s international surveillance program.

During the first wave of the pandemic, the Southern Hemisphere saw a significant decline in flu activity. Australia, South Africa, and Argentina reported just a few cases,4 even less activity than in off-season periods.5 This phenomenon is owed to individual and collective protective measures (masks, physical and social distancing, hygiene, etc.),6,7 which are factors that limit the transmission of SARS-CoV-2 and other respiratory viruses, including the flu. The decline in the number of analyses performed and the “blackout” of surveillance networks that suspended flu sampling could have a noteworthy impact on this equation.

The Valladolid NIC processed between 900 and 1200 flu samples per year in the last decade, with successful culture of 30%–40% of them. The periodic shipment of cultured flu virus samples from the Valladolid NIC to the WHO collaborating center (London, England) has provided relevant information for vaccine formulations. As a result of the current situation, this system is in grave danger, given that no cases of flu symptoms were detected as of week 13 of the 2019–2020 season (Fig. 1) whereas in the previous season, this occurred in week 21. These data, along with the absence of periodic weekly information on flu circulation, force one to seriously contemplate the impossibility of Spain properly reporting flu activity during the next season.

Figure 1.

Number of weekly flu cases reported by Spain to the WHO through the GISRS (Global Influenza Surveillance and Response System) during the 2018–2019 and 2019–2020 seasons. Data from week 40 of 2018 to week 45 of 2020.

Adapted from: FluNet (, Organización Mundial de la Salud (2020).11


The diagnostic demand of COVID-19 during the pandemic has made it so that many laboratories have devoted greater efforts to SARS-CoV-2 diagnostic analyses.8 However, other centers that are specifically aimed at surveillance, such as the NICs, continue carrying out diagnoses of various respiratory viruses, including influenza and SARS-CoV-2. This way, it will be possible to continue simultaneously monitoring influenza and other respiratory viruses in cases without a clinical suspicion of COVID-19 and thus also detect other coinfections between these viruses.9 But to do so, it is necessary to supplement the work of Spanish NICs with shipments of respiratory samples of suspected flu infections and other randomly selected samples from the corresponding sentinel network during the flu surveillance period in order to verify the diagnosis and isolation of flu viruses without detriment to other virus types, including SARS-CoV-2.

The national annual report on the 2019–2020 season has been delayed by four months, despite having epidemiological data on flu circulation up to the month of March 2020. There is also uncertainty about whether surveillance based on the sentinel networks will be available in the upcoming 2020–2021 flu season. The only information available is declarations of intentions on the future organization of flu surveillance in Spain, which is included on the European Centre for Disease Prevention and Control (ECDC) website.10

To the extent known, it is expected that this surveillance will fall to hospitals. They have already shown their reticence in this regard due to the extra workload and financial burden it entails and because of the existence of specialized centers such as the NICs, whose role is precisely what they want to now make the hospitals’ responsibility.

For all of these reasons, this letter would like to warn that, while there is still time, we must, both from the federal government and the autonomous communities, specifically and especially support and promote flu surveillance being done at the three Spanish NICs (Valladolid, Madrid, and Barcelona) and the sentinel networks in order to continue supplementary, coordinated surveillance during the COVID-19 pandemic. This would ensure we do not allow “robbing Peter to pay Paul.”


The research has not received specific grants from agencies in the public, commercial, or non-profit sectors.

Conflict of interest

The authors declare that they have no conflicts of interest.

G. Saint-Pierre Contreras, G. Muñoz Gomez, F. Silva Ojeda.
En búsqueda de otros virus respiratorios durante la pandemia COVID-19.
Rev Clin Esp, 4 (2021), pp. 247-248
J. Owen.
WHO warns that averting flu pandemic may be harder as surveillance switches to COVID-19.
BMJ, 369 (2020), pp. m2441
S.J. Olsen, E. Azziz-Baumgartner, A.P. Budd, L. Brammer, S. Sullivan, R. Fasce-Pineda, et al.
Decreased influenza activity during the COVID-19 pandemic — United States, Australia Chile, and South Africa, 2020.
MMWR Morb Mortal Wkly Rep, 69 (2020), pp. 1305-1309
B. Bohn, A. Wilde, S. Moore, M. Song, C. Patross, A. Junkins, et al.
The incidence of common respiratory viruses during the COVID-19 pandemic: results from the Louisville COVID-19 epidemiology study.
J Respir Infect, (2020), pp. 1-5
T. Itaya, Y. Furuse, K. Jindai.
Does COVID-19 infection impact on the trend of seasonal influenza infection? 11 countries and regions, from 2014 to 2020.
Int J Infect Dis, 97 (2020), pp. 78-80
J. García-Cruces, R. López Izquierdo, M. Domínguez-Gil, M. López-Urrutia, M. de Frutos, B. Lorenzo, et al.
Análisis de la demanda de detección de SARS-CoV-2 en un área de salud de España.
Rev Clin Quimioter, 33 (2020), pp. 422-429
E. Cuadrado-Payán, E. Montagud-Marrahi, M. Torres-Elorza, M. Bodro, M. Blasco, E. Poch, et al.
SARS-CoV-2 and influenza virus co-infection.
Operational considerations for influenza surveillance in the WHO European Region during COVID-19: interim guidance.
World Health Organization (WHO). FluNet Charts for Influenza virus detections [Accessed 19 Nov 2020]. Available from:

Please cite this article as: Sanz-Muñoz I, Ortiz-de-Lejarazu-Leonardo R, Eiros-Bouza JM. Vigilancia internacional de la gripe en tiempos de COVID-19: ¿desvestir un santo para vestir a otro? Rev Clin Esp. 2021;221:372–374.

Copyright © 2021. Elsevier España, S.L.U. and Sociedad Española de Medicina Interna (SEMI)
Revista Clínica Española (English Edition)

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