Winter 2020-2021 will probably remain as an anomaly in the statistical series of epidemiological researchers. Not just because an emerging virus, SARS-CoV-2, caused a pandemic, but also because the health measures adopted to curb its spread have quelled almost all other usual winter epidemics.
Wearing a mask, washing your hands, but above all closing places where there is a lot of mixing (bars, restaurants, etc.) have slowed down the circulation of other viruses which are mainly transmitted by respiratory droplets and aerosols.
Influenza circulation remains very low
Dreaded every winter, the flu has not yet crossed the epidemic threshold this year. The latest epidemiological bulletin on influenza published by Public Health France on February 3 note that there is for the moment “No active circulation of influenza viruses identified by dedicated surveillance networks”. The researchers specify that “Since October 5, 2020, no serious case of influenza has been reported by the services participating in this surveillance”.
Data from the three French health surveillance networks (the Oscour network, which includes more than 600 emergency services; the SOS-Médecins network, with its 60 associations in France; and the Sentinelles network, which has more than 1,400 doctors general practitioners and pediatricians) lead to the same observation: the circulation of influenza viruses is at its lowest.
“A very low level probably due to the impact of public health and social distancing measures”
The situation is not specific to France. “The flu season in Europe usually started around this time of year, but despite regular efforts to screen for influenza, influenza activity remains at a very low level, possibly due to the impact of the measures. of public health and social distancing adopted to curb the transmission of SARS-CoV-2 ”, write experts from the World Health Organization (WHO) and the European Center for Disease Prevention and Control (ECDC) on the surveillance network for Europe Flu News Europe.
In the southern hemisphere, works published in September 2020 – either at the end of the austral winter – by the FluNet collective of the WHO concluded that only 0.06% of people who had undergone samples in Chile, South Africa and Australia tested positive for the viruses of influenza, up from 13.7% in the previous two years.
Be careful, however: influenza epidemics can occur late in winter, and it is not uncommon for them to peak in February or March in the Northern Hemisphere. We will therefore have to wait a little longer before we can speak with certainty about a winter without flu.
Gastroenteritis and bronchitis at its lowest
The findings for influenza are also valid for other seasonal viruses that we are accustomed to encounter between November and March, such as gastroenteritis (rotavirus, norovirus, enterovirus, sapovirus, etc.). This common infection of the wall of the intestine or the stomach caused a low level of emergency visits or consultations with SOS-Médecins during this winter. However, this increases slightly but continues since the second confinement, in November 2020.
As these viruses are transmitted mainly through contaminated surfaces or direct contact, they are sensitive to measures allowing less mixing of people, as well as to hand disinfection.
A joint study by epidemiologists at Emory University in Atlanta and the U.S. Centers for Disease Control and Prevention (CDC), pre-published at the end of November 2020, confirmed that health measures taken in the nine US states studied reduced the circulation of noroviruses by 61%.
The same goes for bronchitis, mainly caused by several families of viruses. The rate of medical procedures performed by SOS-Médecins and emergency room visits for acute bronchitis has remained stable, and much lower than that observed in normal times: 23 emergency room visits per 100,000 people during the week of 25 to January 31, against 83 to 108 passages during the four previous years at the same period.
Bronchiolitis on the rise in younger people
Acute bronchiolitis, an infection of the bronchi affecting mainly infants and young children – caused mostly by respiratory syncytial virus (RSV) – has not reached epidemic level in the country so far either. Data from emergency room visits and the SOS-Médecins network indicate very low activity in 2020. The number of medical procedures concerning this infection is, on the other hand, in clear increase since the beginning of the year 2021, and is approaching levels of previous years.
According to the epidemiological bulletin of Public Health France published on February 3, 1,017 children under two years of age were admitted to the emergency room for bronchiolitis, and just over a third were hospitalized. Ile-de-France and Guyana, particularly affected, are at the pre-epidemic stage. It is therefore not excluded that the circulation of RSV will intensify over the coming weeks.
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