Healthcare systems may look ill-equipped to deal with the rising prevalence of influenza and SARS-CoV-2 in the coming year


In a recent study published in medRxiv* Preprint server Researchers conducted a cohort, community-based study in Managua, Nicaragua, before the onset of winter when influenza A (H3N2) cases are increasing in the Northern Hemisphere.

Study: High prevalence of influenza and SARS-CoV-2.  Image Credit: Guschenkova / Shutterstock
Stady: High circulation combined with influenza and SARS-CoV-2. Image Credit: Guschenkova / Shutterstock

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Close monitoring of the combined circulation of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help understand the cumulative burden on health care facilities facing concurrent respiratory epidemics. This data can help public health officials develop a strategy to counter the combined spread of influenza and SARS-CoV-2 during the winter/autumn season and reduce the burden on the public health care system.

Influenza transmission decreased significantly globally during the first two years of the coronavirus disease 2019 (COVID-19) pandemic. For example, Nicaragua had only five cases of influenza, 80% of which were caused by influenza B, in 2021. However, influenza cases began to rise again in 2022, with a significant increase in influenza circulation in Nicaragua. It’s a worrying trend as the typical flu season approaches in the northern hemisphere.

about studying

In the current study, researchers examined influenza, SARS-CoV-2 infection, and co-infection between January 1 and July 20, 2022 in participants in a home influenza study conducted in Nicaragua. They collected respiratory samples from study participants who visited the clinic with fever, conjunctivitis, rash, or loss of taste or smell.

Furthermore, the researchers tested these samples for influenza using CDC and SARS-CoV-2 protocols by reverse transcription polymerase chain reaction (RT-PCR). Notably, they also collected samples from other family members of participants who tested positive for influenza or SARS-CoV-2.

Furthermore, the researchers calculated the incidence rates for each pathogen using the Poisson distribution and compared the observed and predicted co-infections using the chi-squared test. Finally, they calculated influenza and SARS-CoV-2 attack rates by dividing the number of cases of each pathogen by the total number of study participants.

Results

The study population consisted of 2117 participants aged 0-89 years, 62.5% of whom were female. Gender did not affect the incidence rates of both diseases. The researchers observed 433 influenza infections and 296 SARS-CoV-2 infections, with incidence rates of 37.6 and 26 per 100 person-years, 95% confidence interval (CI), respectively. Notably, influenza infection rates peaked in children aged five years or younger and then decreased steadily.

Interestingly, age-disaggregated SARS-CoV-2 infection rates showed a slight V-shaped trend. In addition, 174, 105, and 38 families suffered from influenza and SARS-CoV-2, both infections. Residents with co-infections did not require hospitalization, but most had a fever compared to those with only COVID-19. Despite the high levels of hybrid immunity in the study population, more cases of SARS-CoV-2 were severe/moderate than influenza. Moreover, more SARS-CoV-2 infection is associated with cough, muscle pain, and joint pain than influenza, although both initially started with fever and upper respiratory symptoms.

The authors note that influenza A and SARS-CoV-2 ran for 22 weeks out of 29 studies. Influenza and SARS-CoV-2 attack rates were 20.1% and 13.6%, which remained strikingly comparable even when standardized for the United States (US) age distribution. Post-consolidation attack rates for influenza and SARS-CoV-2 specifically were 17.2% for influenza and 14.3% for SARS-CoV-2.

In people aged 2 to 14 years, the influenza attack rate was 26.8%, while it was 15.3% for SARS-CoV-2. Compared to previous influenza incidence rates, the incidence of influenza A in 2022 was much higher at 28.6 per 100 person-years. Moreover, the researchers noted roughly the expected number of influenza symptoms and infection associated with SARS-CoV-2.

Conclusions

The study highlighted the double burden of influenza A and SARS-CoV-2 within a community group of families in Managua, Nicaragua. The combined circulation persisted for an astounding 75.9% of the duration of the study. Furthermore, there were nearly as many cases of comorbidity as would have arisen if these pathogens were circulated independently. Overall, the study results portrayed a significant burden on the health care system.

It is worrying that the US population is much older than the study group. Thus, similar levels of co-cycling could have led to more severe cases in the United States. In addition, vaccination coverage remains low among those under 12 years of age. Given the high attack rates of both viruses in children, this would lead to significant morbidity and further school disruption. Given the high risk of a double pandemic of influenza and SARS-CoV-2, vaccine coverage for both influenza and SARS-CoV-2 is imperative before the upcoming influenza season.

*Important note

medRxiv publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.

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