Influenza and COVID-19 Vaccination Impacts on Health Outcomes

Annual immunisation against influenza and the global rollout of COVID-19 vaccines have transformed the landscape of respiratory disease prevention. Influenza vaccines reduce seasonal morbidity and mortality by eliciting strain-specific antibody responses, while COVID-19 vaccines have demonstrated high effectiveness against severe disease and hospitalisation. Beyond their primary targets, mounting evidence suggests potential cross-protective benefits, whereby influenza vaccination may prime innate immunity and reduce the incidence or severity of SARS-CoV-2 infection. Conversely, concerns about immune interference or safety in co-administration scenarios have prompted rigorous clinical evaluation of combined regimens. Together, these investigations inform public health strategies that aim to maximise coverage, optimise timing and sequence, and ensure that concurrent delivery does not compromise immunogenicity, safety or overall health outcomes. The global significance of these findings extends from individual risk reduction to alleviating healthcare burdens during overlapping epidemic waves.

Research from Nature Portfolio

Analyses of large immunisation databases have revealed an association between recent receipt of non-COVID-19 vaccines, including seasonal influenza preparations, and lower rates of SARS-CoV-2 infection. In one exploratory study of over 100 000 individuals tested for the virus, those with documented influenza vaccination within five years exhibited reduced infection rates after adjustment for demographic and clinical confounders. This work proposes that existing vaccines may induce long-lasting innate immune training, fine-tuning antiviral responses and suggesting a wider role for established immunisation programmes in the face of emerging pathogens.

Influenza and COVID-19 Vaccination Impacts on Health Outcomes publication trend

The graph below shows the total number of articles in influenza and covid-19 vaccination impacts on health outcomes across all publications each year (not limited to Nature Index journals).

Technical terms

Immunogenicity: The ability of a vaccine to provoke an immune response, typically measured by antibody titres or cellular activation.

Reactogenicity: The property of a vaccine to cause expected, transient adverse reactions such as injection-site pain or mild fever.

Seroconversion: The transition from seronegative to seropositive status, indicating detection of specific antibodies following vaccination or infection.

Haemagglutination inhibition titre: A laboratory measure of vaccine-induced antibodies that block viral haemagglutinin from agglutinating red blood cells, expressed as the highest dilution achieving inhibition.

References

1. Induction of trained immunity by influenza vaccination - impact on COVID-19. PLOS Pathogens (2021).
2. Exploratory analysis of immunization records highlights decreased SARS-CoV-2 rates in individuals with recent non-COVID-19 vaccinations. Scientific Reports (2021).
3. Safety and immunogenicity of a high-dose quadrivalent influenza vaccine administered concomitantly with a third dose of the mRNA-1273 SARS-CoV-2 vaccine in adults aged ≥65 years: a phase 2, randomised, open-label study. The Lancet Respiratory Medicine (2022).
4. Timing and sequence of vaccination against COVID-19 and influenza (TACTIC): a single-blind, placebo-controlled randomized clinical trial. The Lancet Regional Health - Europe (2023).
5. The Association between Influenza Vaccination and COVID-19 and Its Outcomes: A Systematic Review and Meta-Analysis of Observational Studies. Vaccines (2021).