To investigate the association between prior influenza vaccination and the risk of acute myocardial infarction and stroke following breakthrough influenza infections.
Key Findings:
Cardiovascular events clustered in the 7 days following a positive influenza test, with an adjusted incidence rate ratio (IRR) of 3.5 for acute myocardial infarction and stroke combined.
The risk was higher for acute myocardial infarction (IRR, 4.7) than for stroke (IRR, 2.9).
Prior vaccination was associated with about half the excess cardiovascular risk, with an adjusted IRR of 4.7 in unvaccinated episodes vs 2.4 in vaccinated episodes, indicating a significant interaction between vaccination status and post-infection risk.
The highest risk occurred in the first 3 days following infection (IRR, 5.2), declining to baseline by days 15 to 28.
Interpretation:
Vaccination against influenza significantly reduces the risk of cardiovascular events following infection, particularly in the immediate days post-infection, highlighting its importance in public health strategies.
Limitations:
The study used specimen collection date rather than symptom onset, potentially underestimating risk.
It could not account for yearly variation in vaccine effectiveness and likely underrepresented milder influenza infections.
Residual confounding from co-circulating pathogens or environmental factors could not be excluded.
Conclusion:
Prior influenza vaccination is associated with a significant reduction in the risk of acute myocardial infarction and stroke following influenza infection, underscoring the importance of vaccination in preventing serious cardiovascular events.
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