In a recent study posted to the medRxiv* pre-print server, researchers conducted a community-based prospective cohort study in Managua, Nicaragua, before the start of the winter season when influenza A (H3N2) cases surge within the Northern Hemisphere.

Study: High co-circulation of influenza and SARS-CoV-2. Image Credit: Guschenkova/Shutterstock

Background

Closely monitoring influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) co-circulation could help understand the cumulative burden on healthcare facilities faced with simultaneous respiratory epidemics. This data could help public health officials devise a method to counter high co-circulation of influenza and SARS-CoV-2 through the winter/fall season and ease the burden on the general public healthcare system.

Influenza transmission markedly decreased globally through the first two years of the coronavirus disease 2019 (COVID-19) pandemic. For example, Nicaragua had just five cases of influenza, of which 80% were brought on by influenza B, in 2021. Nevertheless, influenza cases began surging again in 2022,  with a considerable increase in influenza circulation in Nicaragua. It’s a worrisome trend as the standard Northern Hemisphere influenza season is approaching.

Concerning the study

In the current study, researchers examined influenza, SARS-CoV-2 infections, and coinfections between January 1 and July 20, 2022, within the participants of the Household Influenza Cohort Study held in Nicaragua. They collected respiratory samples from study participants who visited the clinic upon developing fever, conjunctivitis, rash, or lack of taste or smell.

Further, the researchers tested these samples for influenza using the Center of Disease Prevention and Control (CDC) protocols and SARS-CoV-2 by real-time reverse transcription-polymerase chain response (RT-PCR). Notably, additionally they collected samples from other household members of those participants who tested positive for either influenza or SARS-CoV-2.

Moreover, the researchers calculated the incident rates of every pathogen using a Poisson distribution and compared the observed and expected coinfection cases using the chi-squared test. Finally, they calculated the attack rates of influenza and SARS-CoV-2 by dividing the variety of cases of every pathogen by the entire variety of participants enrolled within the study.

Study findings

The study population comprised 2117 participants aged 0-89 years, of which 62.5% were females. Gender didn’t affect the incidence rates of each diseases. The researchers noted 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. Notably, the influenza incidence rates peaked in children aged five years or less after which decreased steadily.

Intriguingly, age-stratified SARS-CoV-2 incidence rates displayed a slight V-shaped trend. As well as, 174, 105, and 38 households experienced influenza, SARS-CoV-2, and each infections. The coinfected population didn’t require hospitalization, but most had fever in comparison with those with only COVID-19. Despite high levels of hybrid immunity within the study population, more SARS-CoV-2 cases were severe/moderate than influenza. Furthermore, more SARS-CoV-2 infections presented with cough, myalgia, and arthralgia in comparison with influenza, although each initially began with fever and upper respiratory symptoms.

The authors noted influenza A and SARS-CoV-2 co-circulation for 22 of 29 study weeks. 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 US (US). Post-standardization attack rates for influenza and SARS-CoV-2 specifically were 17.2% for influenza and 14.3% for SARS-CoV-2.

In two to 14-year-olds, the influenza attack rate was 26.8%, whereas it was 15.3% for SARS-CoV-2. In comparison with prior influenza incidence rates, the 2022 incidence rate for influenza A was substantially higher at 28.6 per 100 person-years. Moreover, the researchers observed nearly the expected variety of symptomatic influenza and SARS-CoV-2 coinfections.

Conclusions

The study highlighted the twin burden of influenza A and SARS-CoV-2 inside a community-based cohort of households in Managua, Nicaragua. The co-circulation persevered for a staggering 75.9% of the study duration. Furthermore, there have been nearly as many coinfection cases as would have surfaced if these pathogens circulated independently. Overall, the study findings depicted a considerable burden on the healthcare system.

It’s worrisome that the US population is older than the study cohort; hence, similar levels of co-circulation would have led to more severe cases within the US. As well as, vaccination coverage stays low amongst those under 12 years. Considering the high attack rates of each viruses in children, this might lead to substantial morbidity and further school disruptions. Considering the numerous risk of dual epidemics of influenza and SARS-CoV-2, vaccine coverage for each influenza and SARS-CoV-2 is imperative before the approaching influenza season.

*Vital notice

medRxiv publishes preliminary scientific reports that usually are not peer-reviewed and, due to this fact, mustn’t be thought to be conclusive, guide clinical practice/health-related behavior, or 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. medRxiv. doi: https://doi.org/10.1101/2022.09.13.22279740 https://www.medrxiv.org/content/10.1101/2022.09.13.22279740v1