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COVID-19 mitigation efforts considerably lower influenza exercise

Strategies to contain the spread of COVID-19 appear to be reducing the transmission of influenza in the US, Australia, Chile and South Africa. These strategies can boost influenza vaccines, especially for high-risk populations during seasonal influenza transmission.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel coronavirus, was first detected in Wuhan, Hubei Province, People’s Republic of China, at the end of December 2019. Subsequently, SARS-CoV-2 spread quickly and led to the COVID-19 pandemic. COVID-19 overshadows other similar respiratory illnesses like influenza. Sonja J. Olsen et al. Report in CDC’s weekly report on morbidity and mortality that positive influenza cases (from US respiratory samples) fell from> 20% to 2.3% during this pandemic.

The countries of the southern hemisphere also point to the same observation with low levels of influenza activity. A low incidence of symptoms of influenza is reported and few have tested positive in those who have tested for influenza. Interventions to transmit SARS-CoV-2 as well as influenza vaccination could be the reason for the low influenza activity in the US and worldwide.

Remedial actions in the face of the COVID-19 pandemic have included individual actions such as wearing masks, staying at home while sick, and social distancing, as well as community actions such as school closings, bans on mass gatherings and orders at home, and others. B. Compulsory 14-day travel quarantines, curfews and lockdowns.

Initially, people with respiratory symptoms were preferred to be tested for SARS-CoV-2. This could be due to the observed decline in the influenza virus. However, public health officials and clinicians later began testing samples for influenza. Appropriate numbers were tested and little or no influenza virus was detected compared to the incidence of influenza activity in the previous year.

Australia tested more samples for influenza, typically when the southern hemisphere influenza epidemics peak. They also saw few positive results despite the low strict criteria for testing breath samples compared to previous seasons.

While the temperate climate of the southern hemisphere has virtually no influenza virus circulation, a decline has been observed in the United States, other northern hemisphere countries, and the tropics.

The decline in influenza may be due to a decrease in the number of people checking for or reporting respiratory illnesses, as well as changes in the influenza virus’ circulation. The influenza virus (Ro = 1.28) is low compared to SARS-CoV-2 (R0 = 2-3.5). Although influenza, like SARS-CoV-2, is also primarily transmitted by droplets, the mitigation measures taken during this pandemic period have significantly reduced influenza transmission.

Number of Respiratory Samples Tested and Percentage Influenza Positive Tests per Year – United States, 2016-17 through 2019-20 season

Importance of the report

Populations at high risk of developing serious illnesses and complications from influenza may further customize harm control measures during the influenza season in addition to taking the influenza vaccine. This can be useful for people at high risk, old age, and also reduce the burden of medical care.

Number of samples tested and percent positive influenza test per year - Australia, Chile, and South Africa, April-August (weeks 14–31), 2017–20

Number of samples tested and percent positive influenza test per year – Australia, Chile, and South Africa, April-August (weeks 14–31), 2017–20

The authors agree that it is difficult to separate the effects of general mitigation measures on influenza transmission during this season. For example, school children are spreading influenza, and closing schools can be effective in reducing the spread of influenza. However, because adults are exposed to different exposures, the efficacy of influenza transmission cannot be demonstrated this season.

According to the authors, the results in this report have at least four limitations:

  1. Although the results are consistent and convincing in several countries, an ecological analysis cannot identify the cause.
  2. A sharp decline in global travel and increased use of influenza vaccinations – factors that were not considered in this study – may play an important role in reducing influenza
  3. Viral interference: This could help explain the shortage of influenza during a pandemic caused by another respiratory virus that could outperform airway influenza
  4. It’s also possible that the decline in influenza seen in the United States is just a natural end to the influenza season. However, after March 1, 2020 (declaration of a national emergency related to COVID-19), a sharp decline in influenza-positive cases was observed.

Influenza spread will continue to be monitored to see if activity continues at low levels after mitigation measures are removed. However, in the current uncertain circumstances, it is important to plan and prepare for seasonal influenza circulation, particularly in the 2020–21 season in the northern hemisphere. Additionally, a new Food and Drug Administration (FDA) -approved multiplex diagnostic test to detect SARS-CoV-2 and influenza viruses could improve predictive measures and guide our harm reduction strategies for both diseases.

Given the impending fact that this season the SARS-CoV-2 and the influenza virus could circulate together, influenza vaccination is the best method of influenza prevention (for anyone 6 months and older). Taking the caveats into account, the authors conclude that the widespread implementation of measures to mitigate the transmission of SARS-CoV-2 is linked to the decline in influenza incidence – which is real and simultaneous with the COVID-19 pandemic seems to be.


Journal reference:

  • Olsen SJ, Azziz-Baumgartner E., Budd AP, et al. Decreased Influenza Activity During COVID-19 Pandemic – USA, Australia, Chile and South Africa, 2020. MMWR Morb Mortal Wkly Rep 2020; 69: 1305-1309. DOI: http://dx.doi.org/10.15585/mmwr.mm6937a6

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