# SARS-CoV-2 and Influenza Co-Circulation and Co-Vaccination: A Narrative Review

## TL;DR

This review discusses the overlapping spread of SARS-CoV-2 and influenza viruses and the benefits of combining their vaccinations to improve public health outcomes.

## Contribution

The paper provides a comprehensive analysis of co-circulation and co-vaccination strategies for SARS-CoV-2 and influenza, emphasizing their combined public health impact.

## Key findings

- Co-infection with SARS-CoV-2 and influenza increases risks of severe respiratory outcomes like pneumonia.
- Combined vaccination is convenient, improves compliance, and reduces healthcare burden.
- Available vaccines for both viruses are effective, immunogenic, and safe.

## Abstract

Background/Objectives: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus are dangerous respiratory pathogens with high pandemic potential. Since 2021, these two viruses have been co-circulating, which implies additional risks of co-infection with both pathogens. Prophylactic vaccination is widely recognized as the most effective way to prevent COVID-19 and influenza and to reduce the severity of these diseases. This review analyzes recent data on the simultaneous circulation of influenza and SARS-CoV-2 viruses worldwide, including epidemiological data and the pathogenetic mechanisms of co-infection. Next, we focus on current approaches to simultaneous and combined vaccination against influenza and COVID-19. We outline the types of vaccines and summarize the available findings on the effectiveness and safety of co-vaccination. Methods: A comprehensive search was conducted using PubMed, Scopus, Web of Science, and ClinicalTrials to identify data relevant to SARS-CoV-2 and influenza co-circulation and dual vaccination. Results: Influenza and SARS-CoV-2 cause similar symptoms, and co-infection can significantly enhance the risks of pneumonia and acute respiratory distress syndrome progressing with a poor outcome, especially among children and the elderly. A range of influenza and COVID-19 vaccines built on different technological platforms is currently available on the market, with proven effectiveness, immunogenicity, and safety. A co-vaccination approach is more convenient for patients and is associated with better response to treatment, while also improving vaccine coverage and compliance and offering significant resource savings for healthcare systems. Conclusions: The concurrent circulation of SARS-CoV-2 and influenza viruses presents a growing public health challenge. Simultaneous and combination vaccination strategies have emerged as effective tools to streamline immunization, enhance protection, and reduce healthcare burden. Future studies should elucidate the mechanisms of the exacerbation of respiratory disease caused by co-infection, as well as the optimal strategies for co-administering influenza and COVID-19 vaccines for long-term control of seasonal and potentially pandemic respiratory viruses.