Research reveals higher risk of stroke 1 month after flu infection

Can getting the flu also increase your risk of cardiovascular disease? Research has found that within one month after a flu infection, a patient's chance of having a myocardial infarction increases significantly, and the risk of stroke can surge by up to five times. A doctor advises that if eight specific symptoms appear after a flu infection, they could be warning signs of cardiovascular disease, and immediate medical attention should be sought.

Internal medicine physician Dr. Fu Yu-cheung stated on his Facebook page that many people generally believe there is nothing to be worried about after recovering from the flu. However, the latest research confirms that the one-month period following a flu infection is a "high-risk period" for heart disease and cerebrovascular disease. Besides the influenza virus, infections with other viruses like shingles (herpes zoster), Hepatitis B and C, and even RSV are also associated with an increased long-term risk of cardiovascular disease. The related research was published in the Journal of the American Heart Association in November this year.

This research, by integrating and analyzing 155 relevant literature pieces, found that infections with different viruses all increase the risk of heart and cerebrovascular events:

• Flu infection within the first month of onset causes the risk of acute myocardial infarction to surge by 4.01 times, and the risk of stroke reaches as high as 5.01 times.
• COVID-19 infection increases the risk of coronary heart disease by 27 percent, and the chance of stroke also rises by 23 percent.
• Shingles (herpes zoster) virus infection is significantly correlated with a 12 percent increase in coronary heart disease risk and an 18 percent increase in stroke risk.

The study also pointed out two pathways through which viral infections trigger cardiovascular events:

1. Indirect Attack (Immune Storm): The virus triggers an excessive immune response, causing systemic inflammation, which leads to damage to vascular endothelial tissue, accelerated blood clot formation, and atherosclerosis.
2. Direct Attack (Myocardial Invasion): Some types of viruses can directly invade myocardial cells, causing viral myocarditis or arrhythmias. This explains why cases of acute myocardial infarction (AMI) can occur after infection in clinical practice.

The research shows that even without risk factors like hypertension, diabetes, or smoking, young people can still suffer sudden strokes or myocardial infarctions shortly after being infected with the flu or COVID-19. The key lies in the fact that the inflammatory response is a systemic event. When the body is attacked by a virus, it leads to increased blood viscosity and constriction of blood vessels, making the heart and brain instantly bear pressure beyond the norm.

The authors of the study particularly emphasized that actively preventing flu and other viral infections is itself an important part of cardiovascular disease prevention. The protective effect of vaccination does not come from the virus components themselves but from the stable response generated after the immune system is 'trained'. They recommend vaccination to reduce related risks:

• Flu Vaccine: Can reduce the risk of myocardial infarction and stroke by approximately 20 percent to 40 percent.
• Shingles Vaccine: Can reduce the chance of cardiovascular disease by up to 23 percent.
• COVID-19 Vaccine: Significantly reduces the probability of cardiovascular complications after infection.

Fu reminds everyone that winter is the high-incidence season for respiratory infectious diseases. Influenza, RSV, adenovirus, and even pneumococcus often circulate simultaneously. If these infections and cardiovascular events like stroke and heart disease have a superimposed effect, health risks are amplified. 

Many elderly people often mistakenly believe that if they already have heart disease, they are not suitable for vaccination. But the reality is exactly the opposite; cardiovascular disease patients are the group most in need of vaccine protection because a viral infection can significantly increase the heart's burden and prolong the recovery period.

Seek Immediate Medical Attention if 8 Symptoms Appear After Flu 

Fu stated that if the elderly develop the following symptoms within one to four weeks after infection, they should seek medical attention immediately and not delay for observation. These signs are often not simply a lingering cold but important warnings of heart or cerebrovascular disease:

• Sudden chest tightness
• Shortness of breath / Rapid breathing
• Cold sweats
• Weakness in hands or feet
• Slurred speech
• Facial drooping
• Irregular heartbeat (suddenly fast or slow)
• Unexplained fatigue

Influenza A / Influenza B – Which Has the Highest Mortality Rate?

According to the Department of Health, seasonal influenza is an acute respiratory disease caused by influenza viruses. There are three known types of seasonal influenza viruses that infect humans: A, B, and C. Influenza A and B account for the majority of infections, and over the years, flu outbreaks are usually associated with type A viruses.

1. How to distinguish Influenza A?
   • Common Symptoms: Fever, chills, headache, cough, sore throat, and runny nose.
   • High-Risk Groups: The elderly, young children, or immunocompromised individuals may develop complications like bronchitis or pneumonia after infection, and in severe cases, encephalitis, myocarditis, or pericarditis, which can be fatal.
   • Severity/Mortality: The condition is generally more severe, with a higher mortality rate.
   • Infectivity: Higher transmission and pathogenicity; currently the main influenza virus causing pandemics. When new influenza A subtypes appear, they can potentially cause new flu outbreaks.
2. How to distinguish Influenza B?
   • Common Symptoms: Similar to Influenza A.
   • Infectivity/Severity/Mortality: The condition is generally milder than Influenza A, with a lower mortality rate. The rate of evolution is two to three times lower than that of the Influenza A virus.

The Department of Health states that the peak flu season is generally from January to March each year, and sometimes in April and July to August. Most people can recover on their own after getting the flu. Those with milder symptoms should get plenty of rest and drink lots of water. If flu symptoms appear, one should not go to work or school. If symptoms persist or worsen, seek medical consultation immediately.