Impact of COVID-19 on the dynamics of respiratory viruses

The impact of the COVID-19 pandemic and its associated lockdown on the circulation of other respiratory viruses is enormous. The natural course of seasonal viral infections has been deeply modified. A delayed or even non-existing respiratory syncytial virus (RSV), influenza, and rhinovirus season were seen in e.g. France, the UK, Italy, and Switzerland. These off-season viral epidemics might be explained by the COVID-19 measures. Delayed RSV epidemics may be a burden to healthcare systems that are already strained because of COVID-19.

There has been a dramatic global reduction in cases of respiratory seasonal viruses during the COVID-19 pandemic. Non-medical measures, such as social distancing, appear to have had a big impact on the course of natural epidemics of other respiratory viruses, including RSV.

In the first presented study, Prof. Ralph Epaud (Paediatric Hospital Crétiel, France) and his team aimed to assess the course of RSV infection in France during the 2020–2021 season, and compared it with the 2 previous RSV seasons (2018–2019 and 2019–2020) [1,2]. French national data for bronchiolitis in children under 2 years of age from 3 networks was analysed, including data from emergency departments (ED), general practitioners (GPs), and hospital laboratories. The RSV-positive tests during these visits were compared to the RSV-positive tests of the previous 2 RSV seasons.

During the 2020–2021 season, the RSV epidemic started in February 2020, which is 12 weeks later compared with the previous seasons (see Figure). The highest number of bronchiolitis cases was reported during the end of March 2021, almost 10–12 weeks later than the previous seasonal peaks. In addition, the total number of cases was lower than in the previous seasons. The absence of a normal RSV epidemic is presumed to be a result of COVID-19 restrictions, including social distancing. This led to raised concerns regarding the burden of RSV in the already overheated healthcare system because of the COVID-19 pandemic. The occurrence of a delayed RSV epidemic in France could be explained by school and daycare centres that remained open in the second lockdown. Another explanation could come from the fact that despite international travel restrictions, interstate borders remained open, allowing RSV diffusion from other countries.

Figure: Percentage of hospital and ambulatory positive test for RSV all ages, Metropolitan France, week 40 of 2018 till week 19 of 2021 [2]



A second study looked at the incidence of respiratory viruses in a rural district general hospital in Shrewsbury, UK, during the (supposed) peak influenza season [3]. Ms Taya Chapman and colleagues performed a retrospective analysis on all respiratory swab data of hospitalised patients during the third and fourth week of January 2021. Respiratory analysis was done for influenza, RSV, and SARS-CoV-2 simultaneously.

Remarkably, zero patients of the investigated cohort tested positive for influenza or RSV. Of 247 patients, 120 (47%) tested positive for SARS-CoV-2, of which 66 (55%) were male with a mean age of 73 years. Although the sample size was small, the UK cohort reflected the trend of influenza cases represented in the Southern Hemisphere during the peak influenza season [4]. It might be that regular hand washing and masks prevented the spread of other respiratory viruses. Moreover, competitive inhibition of influenza and RSV by SARS-CoV-2 is likely through its binding of sialic acid receptors on the host’s cell surface normally used by influenza viruses to gain entry into cells. However, future studies are needed to study this in vitro.

In a third study, Dr Sergio Ghirardo (Bambino Gesù Children’s Hospital, Italy) explored the effects of SARS-CoV-2 containment measures on bronchiolitis onset, hospitalisation, aetiology, and severity in comparison with the 2 previous years [5]. Dr Ghirardo and his team performed a retrospective study in infants ≤1 year that were hospitalised because of bronchiolitis between 1 September and 31 December 2018, 2019, and 2020. Viral diagnosis was confirmed by PCR test.

The bronchiolitis season onset did not occur significantly later in the year in 2020 (P=0.93). However, the frequency of hospitalisation differed significantly, with only 5 hospitalised patients in 2020 compared with 36 in 2019 and 2018 (reduction of 86.2%). The in-hospital length-of-stay in 2020 was shorter (2.6 days) compared with 4.8 days in 2019 and 4.6 days in 2018 (P=0.02). No patients were submitted to the intensive care unit (ICU) in 2020, while 4 (11%) patients were admitted to the ICU in 2019, and 1 (3%) in 2018. According to the aetiology, rhinovirus accounted for all cases in 2020; no RSV cases were identified. The epidemic respiratory virus season did not start at the end of December 2020 presumably because of COVID-19 measures. Shorter length-of-stay and less ICU admissions suggested less severe disease as a possible consequence of COID-19 measures. Another explanation could be that less severe disease was seen because of a lack of RSV.

In a fourth study, Dr Cristina Ardura-Garcia (Institute of Social and Preventive Medicine, Switzerland) studied the effect of the COVID-19 measures on respiratory symptoms in children previously followed by paediatric pulmonologists [6]. Parents from children of The Swiss Paediatric Airway Cohort, a prospective cohort in Switzerland including children aged 0–16 years, were asked to complete monthly questionnaires on respiratory symptoms and treatment for 1 year. Questionnaires were compared to pre-lockdown questionnaires.

Among 536 questionnaires including 253 children with a mean age of 9 years, 83 were completed during the pre-COVID winter, 91 during lockdown, 258 during the COVID winter, and 104 during spring 2021. Compared to the pre-COVID winter, questionnaires completed in lockdown and in the COVID-winter were less likely to report on respiratory infections (aOR 0.12), cough (aOR 0.31), dyspnoea (aOR 0.30), wheeze (aOR 0.15), treatment for respiratory problems (aOR 0.022), and asthma control-drug use (aOR 0.65). Preventive measures reduced respiratory infections and symptoms drastically in Switzerland during the COVID-19 pandemic compared to the previous period. No further reduction of respiratory infections was seen during school .

In conclusion, an absent or delayed annual seasonal epidemic of most respiratory viruses was reported, likely related to implementation of public health measures because of COVID-19. While continued detection of rhinovirus was noticed, influenza and RSV were absent during the 2020-2021 season with France as an exception experiencing a 3-month delayed RSV season. Usually in the Northern hemisphere, influenza and RSV are known to peak during winter months. However, restrictions of international travel, school closures, and stay-at-home orders may have influenced the spread of these viruses.

1. Epaud R, et al. Late Breaking Abstract - Impact of COVID-19 social distancing on viral infection in France: a delayed outbreak of RSV. Abstract 2849. ERS 2021, 5–8 September.
2. Delestrain C, et al. Pediatr Pulmonol. 2021 Sep 2.
3. Chapman T, et al. Another aspect of COVID pandemic: where has all the Flu gone? Abstract 3255. ERS 2021, 5–8 September.
4. Hills T, et al. Lancet. 2020 Nov 21;396(10263):1633–1634.
5. Ghirardo S, et al. Delayed bronchiolitis season’s onset during COVID-19 pandemic. Abstract 2963. ERS 2021, 5–8 September.
6. Ardura-Garcia C, et al. Effect of COVID19 preventive measures on respiratory infections and symptoms in children. Abstract 2962. ERS 2021, 5–8 September.

 

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Posted on 9 November 20219 November 2021