Vaccine-Related Fainting: Causes and What to Do Next

Q: Vaccine-Related Fainting: Causes and What to Do Next

Dear Ms. Lee： 1. Syncope refers to a transient loss of consciousness and inability to maintain posture due to insufficient cerebral blood perfusion. Its characteristic feature is a rapid recovery of consciousness without the need for treatment. Syncope is a sym

Vaccine injection/syncope

Hello Dr.
Hsiao, my husband received his first dose of the AZ vaccine yesterday, August 4th, at 9:35 AM.
After the vaccination, he stayed at the hospital for 20 minutes and then rode his motorcycle home (a 5-minute ride).
Once home, he started drinking water continuously, consuming about 2,500 cc throughout the day.
He did not engage in any vigorous exercise, just normal walking around the house.
For breakfast, he had scrambled eggs, avocado, and broccoli; for lunch, a bowl of chicken soup; and for dinner, a bowl of clear beef noodle soup.

This morning at 4 AM, he went to urinate and suddenly fainted for about 5 seconds before regaining consciousness on his own.
After sitting on the toilet for 10 minutes, he returned to normal and is currently alert.
There is no swelling in his head, and he does not feel nauseous or dizzy.
However, I am still very concerned and would like to ask the doctor what possible causes there could be.
Should I arrange for any specific tests? Thank you!

Li's, 30~39 year old female. Ask Date: 2021/08/05

Dr. Xiao Yongxun reply Family Medicine

Dear Ms.
Lee:
1.
Syncope refers to a transient loss of consciousness and inability to maintain posture due to insufficient cerebral blood perfusion.
Its characteristic feature is a rapid recovery of consciousness without the need for treatment.
Syncope is a symptom, not a disease; however, it must be distinguished from other conditions that cause altered consciousness, such as epilepsy and metabolic disorders (e.g., hypoglycemia or hyponatremia).
Additionally, life-threatening conditions must be identified and treated urgently.
2.
Approximately 45% of patients with syncope can have the cause identified through a detailed medical history and physical examination.
The causes of syncope can be classified into categories including neurally mediated reflex syncope (about 23% of cases), cardiac syncope (about 18% of cases), cerebrovascular syncope (about 10% of cases), orthostatic or postural syncope (about 8% of cases), psychiatric syncope (about 2% of cases), and idiopathic syncope (about 34% of cases), among others.
3.
As age increases, the likelihood of syncope caused by multiple factors also increases; various factors must sometimes be considered, including pre-existing conditions, newly developed illnesses, and medication side effects.
4.
Based on your description, it is likely that you are experiencing postvoiding syncope, a type of neurally mediated reflex syncope that commonly occurs in middle-aged and older adults.
This means that prior to urination, sympathetic nervous system activity is heightened to prevent involuntary urination; however, once a large volume of urine is released, sympathetic activity suddenly decreases while parasympathetic activity increases, leading to an inability to maintain blood pressure and cerebral perfusion, resulting in syncope.
After collapsing, blood flow back to the heart increases, and sympathetic activity reflexively rises, allowing for a quick recovery of consciousness.
5.
Regarding whether the AstraZeneca vaccine caused the syncope, while this possibility cannot be immediately ruled out, it is considered unlikely.
True cerebrovascular embolism (whether arterial or venous) would likely present with more complex symptoms and a different clinical course.
6.
However, there are still many uncertainties that need clarification; it is not advisable to make a diagnosis at this point.
I recommend that you and your husband discuss this matter in detail with your family physician before making any decisions, or consider visiting a neurology outpatient clinic at a regional hospital or higher for further evaluation.

Reply Date: 2021/08/05

More Info

Fainting, or syncope, after vaccination can be concerning, especially when it occurs shortly after receiving a vaccine like the AZ (AstraZeneca) vaccine. Understanding the potential causes and what steps to take next is crucial for ensuring safety and addressing any underlying issues.

Possible Causes of Fainting After Vaccination
1. Vasovagal Response: One of the most common causes of fainting after vaccination is a vasovagal response. This occurs when the body overreacts to certain triggers, such as pain, fear, or stress, leading to a sudden drop in heart rate and blood pressure. This can result in fainting. It's particularly common in younger individuals and can happen even if the person feels fine immediately after the vaccination.

2. Dehydration or Low Blood Sugar: Although your husband drank a significant amount of water throughout the day, it's still possible that dehydration or low blood sugar could contribute to fainting. If he had not eaten enough or if his body was not adequately hydrated, this could lead to a temporary drop in blood pressure.

3. Postural Hypotension: This condition occurs when a person stands up quickly, causing a sudden drop in blood pressure. If your husband was sitting for a long time and then stood up quickly to go to the bathroom, this could have triggered a fainting episode.

4. Anxiety or Stress: The anticipation of receiving a vaccine can cause anxiety, which may lead to fainting in some individuals. The body's stress response can affect heart rate and blood pressure, leading to syncope.

5. Underlying Medical Conditions: Although your husband appears to be healthy, underlying medical conditions such as arrhythmias or other cardiovascular issues could also contribute to fainting episodes.

What to Do Next
1. Monitor Symptoms: Since your husband regained consciousness quickly and is currently alert and oriented, it’s essential to monitor him for any recurring symptoms. If he experiences additional fainting episodes, dizziness, or any other concerning symptoms, seek medical attention promptly.

2. Hydration and Nutrition: Ensure that he continues to stay well-hydrated and consumes balanced meals. If he has a history of low blood sugar or dehydration, it may be beneficial to keep snacks and fluids readily available.

3. Rest: Encourage him to take it easy for a few days following the vaccination. Avoiding strenuous activities can help prevent further episodes.

4. Consult a Healthcare Provider: Given that he experienced a fainting episode, it would be prudent to consult a healthcare provider. They may recommend a physical examination and possibly some tests, such as blood pressure monitoring, blood tests, or an ECG, to rule out any underlying issues.

5. Follow-Up: If the fainting occurs again or if he experiences other symptoms such as chest pain, shortness of breath, or prolonged dizziness, seek immediate medical attention.

Conclusion
While fainting after vaccination can be alarming, it is often benign and related to a vasovagal response or other non-serious causes. However, it is essential to take such episodes seriously and monitor for any further symptoms. Consulting with a healthcare provider will help ensure that any potential underlying issues are addressed and that your husband remains safe and healthy following his vaccination.

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