Discussion
SARS-CoV-2 and influenza infection are associated with respiratory disorders, and signs in patients can vary from moderate to severe morbidity and mortality (30). Some studies and case reports indicate that influenza co-infection with COVID-19 may be important for the infected patient’s severity (31-34). In this study, the prevalence of co-infection SARS-CoV-2 with influenza A and B, clinical characterization, and chest radiography in co-infected patients with confirmed SARS-CoV-2 infection was meta-analyzed. The results indicated that the prevalence of influenza A is higher than influenza B co-infection in COVID-19 patients (2.3(0.5-9.3) vs. 0.1 (0.4-3.3)). Our findings show that fever and cough were the most common clinical symptoms (86% and 46%, respectively) in co-infected SARS-CoV-2 patients with influenza A or B. In addition, Fatigue, Diarrhea, and Difficult Breathing were the less common clinical findings among co-infected patients (13.8%, 12.2%, and 9.3%, respectively).
Influenza and SARS‐Cov‐2 viruses are transmitted by contact, droplets, and contaminated surfaces and cause respiratory diseases with a broad range of moderate to severe symptoms (35, 36). Based on the basic reproduction number R zero (R0), SARS‐Cov‐2 viruses can infect more people than influenza (1.5–5.7 for SARS‐Cov‐2, 0.9–2.1 for influenza) (36, 37). Several studies have confirmed co-infection of SARS-CoV-2 with influenza A and influenza B, such as studies in the United States (15, 16), China (17), and Iran (18). Some articles have shown that respiratory viruses such as influenza can lead to complications of the disease and even patient death in confirmed cases of COVID-19 (18-20). Some other research had the contrary view they assume that competitive advantage in virus connection can play an essential role in SARS-CoV-2 interactions with other viruses, such as influenza, during co-infection (38, 39). Moreover, different immune response mechanisms can give rise to a competitive advantage between SARS-COV-2 and other co-infecting viruses; therefore, in patients with SARS-CoV-2, the co-infection rate with other viruses, such as influenza, is much lower (38, 39).
The research limitations are the number of studies, small sample sizes, publication bias, heterogeneity of the study, poor quality analysis and reporting in some of the included studies.
Due to the low prevalence of SARS-COV-2, co-infected influenza patients, and many differences between COVID‐19 and influenza, such as transmissibility, mortality rate, laboratory diagnosis, and clinical symptoms (30, 40), these results only suggest that consider the influenza viruses in COVID‐19 suspected patients. As a consequence, this approach will help to select the best treatment protocol for the management of COVID-19 patients and reduce the severity of the disease. People should also be vaccinated against seasonal influenza to reduce the risk of co-infection in the recent pandemic.