In a recent study published on the preprint server medRxiv*, researchers conducted a prospective community-based cohort study in Managua, Nicaragua, before the start of the winter season when cases of influenza A (H3N2) they increase in the northern hemisphere.
Study: High co-circulation of influenza and SARS-CoV-2. Image credit: Guschenkova/Shutterstock
background
Close monitoring of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) co-circulation could help understand the cumulative burden on healthcare facilities facing concurrent respiratory epidemics. These data could help public health officials devise a strategy to counter the high co-circulation of influenza and SARS-CoV-2 during the winter/autumn season and ease the burden on the public health system.
Influenza transmission declined markedly globally during the first two years of the coronavirus disease 2019 (COVID-19) pandemic. For example, Nicaragua had only five cases of influenza, of which 80% were caused by influenza B, in 2021. However, cases of influenza began to increase again in 2022, with a substantial increase in circulation of influenza in Nicaragua. It’s a worrying trend as the typical northern hemisphere flu season approaches.
About the study
In the present study, researchers examined influenza, SARS-CoV-2 infections, and co-infections between January 1 and July 20, 2022, in participants of the Household Influenza Cohort Study held in Nicaragua. They collected breath samples from study participants who visited the clinic after developing a fever, conjunctivitis, rash, or loss of taste or smell.
In addition, the researchers tested these samples for influenza using Centers for Disease Control and Prevention (CDC) protocols and SARS-CoV-2 using real-time reverse transcription polymerase chain reaction (RT- PCR). Notably, they also collected samples from other household members of those participants who tested positive for influenza or SARS-CoV-2.
In addition, the researchers calculated incidence rates for each pathogen using a Poisson distribution and compared observed and expected cases of coinfection using the chi-square test. Finally, they calculated attack rates for influenza and SARS-CoV-2 by dividing the number of cases of each pathogen by the total number of participants enrolled in the study.
Results of the study
The population studied consisted of 2,117 participants between 0 and 89 years of age, of which 62.5% were women. Gender did not affect the incidence rates of both diseases. The researchers observed 433 influenza and 296 SARS-CoV-2 infections, with incidence rates of 37.6 and 26 per 100 person-years, 95% confidence interval (CI), respectively. In particular, influenza incidence rates peaked in children aged five and under and then declined steadily.
Interestingly, age-stratified SARS-CoV-2 incidence rates showed a slight V-shaped trend. In addition, 174, 105, and 38 households experienced influenza, SARS-CoV-2, and both infections. The co-infected population did not require hospitalization, but more had fever compared to those with only COVID-19. Despite high levels of hybrid immunity in the study population, more cases of SARS-CoV-2 were severe/moderate than influenza. In addition, more SARS-CoV-2 infections presented with cough, myalgia, and arthralgia compared with influenza, although both initially started with fever and upper respiratory symptoms.
The authors noted the co-circulation of influenza A and SARS-CoV-2 during 22 of the 29 weeks of the study. Influenza and SARS-CoV-2 attack rates were 20.1% and 13.6%, which remained strikingly comparable even when standardized to the age distribution of the United States ( USA). Post-standardization attack rates for influenza and SARS-CoV-2 were specifically 17.2% for influenza and 14.3% for SARS-CoV-2.
In children aged two to 14, the attack rate for influenza was 26.8%, while it was 15.3% for SARS-CoV-2. Compared to previous influenza incidence rates, the influenza A incidence rate in 2022 was substantially higher at 28.6 per 100 person-years. In addition, the researchers observed nearly the expected number of co-infections of symptomatic influenza and SARS-CoV-2.
Conclusions
The study highlighted the dual burden of influenza A and SARS-CoV-2 within a community-based household cohort in Managua, Nicaragua. Co-circulation persisted for an astonishing 75.9% of the duration of the study. Furthermore, there were almost as many cases of coinfection as would have arisen if these pathogens were circulating independently. Overall, the results of the study represented a substantial burden on the healthcare system.
Of concern is that the US population is larger than the study cohort; therefore, similar levels of co-circulation would have led to more severe cases in the US. In addition, vaccination coverage remains low among children under 12 years of age. Given the high attack rates of both viruses in children, this would lead to substantial morbidity and further school disruption. Given the significant risk of dual epidemics of influenza and SARS-CoV-2, influenza and SARS-CoV-2 vaccine coverage is imperative before the next flu season.
*Important news
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.
Journal reference:
- John Kubale, Aaron M Frutos, Angel Balmaseda, Saira Saborio, Sergio Ojeda, Carlos Barilla, Nery Sanchez, Abigail Shotwell, Alyssa Meyers, Roger Lopez, Miguel Plazaola, Guillermina Kuan, Aubree Gordon. (2022). High co-circulation of influenza and SARS-CoV-2 with Rxiv. doi: