As the new coronavirus spreads, will the influenza virus become a thing of the past?

November 1 is the fourth World Flu Day, and this year's theme is "Influenza and COVID-19, Vaccines to Prevent It". The latest data show that the overall influenza positivity rate monitored in my country in 2021 is lower than the average level before the COVID-19 pandemic. Not only in my country, in fact, seasonal influenza activities in countries around the world have dropped "precipitously" since the beginning of 2020!

Is the influenza virus, which has a history of five pandemics, really gradually becoming a thing of the past?

Low level of influenza prevalence, thanks to NPIs!

"The NPIs implemented against COVID-19 have played an unexpected role in this process." Gao Fu, an academician of the Chinese Academy of Sciences and director of the Chinese Center for Disease Control and Prevention, said that NPIs are non-pharmaceutical interventions (NPIs) implemented by various countries against COVID-19, including personal protection such as wearing masks, maintaining social distance, restricting the flow of people, canceling large-scale gatherings, closing public places, suspending classes, restricting travel, and issuing home recommendations.

Compared with previous seasons, seasonal influenza activity in many countries, including China and the United States, has decreased significantly in 2019-2020. In fact, this low level of influenza activity continued in the following 2020-2021 season. For example, the B/Yamagata influenza lineage was not detected anywhere from April 2020 to August 2021, and it seemed to have "disappeared."

Influenza and COVID-19 have very similar temperaments!

It can be seen that influenza is prevalent at a low level among humans, mainly due to the popularization of new crown prevention and control measures.

In addition, influenza and COVID-19 are inextricably linked. It is no coincidence that they can both cause pandemics.

Liu Jun, a researcher at the Institute of Viral Disease Prevention and Control, Chinese Center for Disease Control and Prevention and deputy director of the National Influenza Center, believes that the reason why they are both able to cause pandemics is because they have similar characteristics.

"They all have the characteristics of respiratory transmission." Liu Jun said that in addition to this main characteristic, there are three other common characteristics: First, the symptoms they cause in humans are diverse, especially the existence of latent or asymptomatic infections and mild conditions, which brings difficulties to case identification and epidemic control; second, their virus variants or reassortant strains continue to appear, and show characteristics such as increased transmissibility, infectivity and immune escape; third, their susceptible animals are very wide, not just one species. For example, the new coronavirus can infect minks and white-tailed deer, and the influenza virus can infect poultry, which provides potential hosts for the emergence and recurrence of the epidemic.

Is influenza a thing of the past?

As the new coronavirus spreads, is the influenza virus gradually becoming a thing of the past?

Experts gave the same answer to this question:

We should be more vigilant!

Although the prevalence of influenza viruses in humans has decreased, avian influenza viruses can still be detected in poultry and migratory birds outside of humans. Data show that in the spring of 2020, the H5N8 avian influenza virus caused multiple poultry outbreaks in Central and Eastern Europe, and before the end of 2020, Russia reported cases of human infection with the H5N8 avian influenza virus.

Gao Fu believes that given the current complex situation of co-epidemic of influenza and COVID-19, we should be more vigilant against seasonal influenza and avian influenza.

In addition, some countries no longer consider the new crown a socially harmful disease and have already or plan to lift social distance restrictions. Liu Jun said that the gradual relaxation of non-drug intervention measures in these countries may lead to an increase in influenza infection rates in the upcoming flu season.

"Under the pressure of COVID-19 prevention and control, although influenza is prevalent at a low level, new influenza variants may emerge." Liu Jun also reminded that mutated or reassorted influenza virus strains may also cause epidemics. In some countries and regions, medical resources may continue to tilt towards COVID-19, which will continue to affect their ability to respond to influenza pandemics. In addition, the increase in cases of other respiratory viruses, including respiratory syncytial virus, will also make the prevention and control of respiratory infectious diseases in future epidemic seasons more complicated.

Note: The five influenza pandemics were the "Spanish flu" (H1N1) in 1918, the "Asian flu" (H2N2) in 1957, the "Hong Kong flu" (H3N2) in 1968, the "Russian flu" (H1N1) in 1977 and the "Mexican swine flu" (H1N1) in 2009.

◎ Science and Technology Daily reporter Zhang Jiaxing

Source: Science and Technology Daily

Editor: Zhang Shuang

Review: Yue Liang

Final review: Liu Haiying