WHO: Prepare for Flu Outbreak in COVID-19 Pandemic

The COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2 continues to have a major impact on healthcare and social systems throughout the world. As the clinical and epidemiological features of COVID-19 have many parallels with influenza, it is important to ensure optimal management of both respiratory diseases as we anticipate their continued co-circulation.

Between the onset of COVID-19 and the summer of 2021, strict public health and social measures taken by countries around the world have resulted in a significant reduction in seasonal influenza cases globally compared to previous years.

However, with the gradual relaxation of immunization restrictions in many countries by the end of 2021, influenza cases increase. Also, as the previous strict quarantine measures reduce people’s exposure to influenza, the immunity of the population to deal with influenza may decrease, which may further affect the incidence of seasonal influenza in the future. Based on global influenza surveillance data: Influenza virus infection rate increases starting in the fall of 2021.

From Dec 6, 2021 to Dec 26, 2021, WHO has tested more than 522,595 samples from 110 countries or territories, a total of 27,153 people were tested positive for influenza virus, of which 19,980 (73.6%) were flu A positive and 7,173 (26.4%) were flu B positive. Among the influenza A viruses, 352 cases were influenza A (H1N1) pdm09 and 7625 cases were influenza A (H3N2). Of the influenza B viruses with distinct characteristics, 3 belongs to B-Yamagata and 6819 belongs to B-Victoria.
Globally, overall influenza activity has begun to recover and continues to increase, especially in temperate regions of the northern hemisphere. In some countries, influenza activity reached the level of the same period in the year before COVID-19.

In North America, the number of influenza hospitalizations increased with the detection of influenza A (H3N2) predominantly, although the overall level remained low. In particular, influenza infection rates in the United States have become similar to those prior to the COVID-19 epidemic and have exceeded the warning line, while the percentage of deaths due to pneumonia, influenza or COVID-19 in the United States has been higher than historical data.

In Europe, influenza activity increased throughout the region, with influenza A (H3N2) predominating. Positive influenza rates at European outpost testing sites have been over 10% for two consecutive weeks. For this reason, experts say that the European flu season is coming. Influenza activity also exceeded seasonal thresholds in several regions of Russia and France.

In East Asia, influenza activity continues to trend upward. In particular, influenza B tests and positivity rates in northern and southern provinces of China continue to increase and reached the level before the outbreak of COVID-19, with B-Victoria virus currently predominating in China.

In addition to Africa, regions with increased global influenza activity include South America, South Asia, and Southeast Asia.

Pathogenicity and diagnostic value of influenza virus
Globally, there are up to 1 billion cases of seasonal influenza each year, with 3-5 million severe cases and as many as 650,000 respiratory-related deaths. Influenza viruses can cause acute infection. In humans, viral shedding begins after about 1 day and peaks before symptoms appear. Typical influenza symptoms include sudden onset of fever, muscle pain, headache and exhaustion, peaking 2-3 days after infection and resolving within 1-2 weeks. However, in rare cases the influenza virus can cause complications from influenza such as bacterial infections or worsening of cardiovascular and respiratory disease, which can lead to death in severe cases.

WHO: Prepare for flu outbreak in COVID-19 pandemic

1. As the rate of positive influenza tests continues to increase during the COVID-19 pandemic, WHO recommends that countries prepare for co-circulation of influenza and SARS-CoV-2. Countries are encouraged to strengthen integrated surveillance for both influenza and SARS-CoV-2 and to enhance influenza vaccination to prevent severe illness and hospitalization due to influenza. Clinicians should consider influenza in the differential diagnosis, especially for those at high risk of influenza, and follow national guidance for testing and treatment.

2. WHO calls for triage of influenza and COVID-19 testing: Influenza and COVID-19 are both respiratory diseases with similar transmission modes. These two viral infections usually have similar symptoms, and only laboratory tests can distinguish between influenza and COVID-19.