This article features a study that put together a large number of people who were vaccinated with the COVID-19 jab and developed a rare bleeding problem called Acquired Hemophilia A.
Seminars in Thrombosis and Hemostasis published the peer-reviewed paper in 2023 Investigating a Signal of Acquired Hemophilia Associated with COVID-19 Vaccination: A Systematic Case Review.
I. Introduction
Imagine suddenly developing large bruises, deep muscle bleeding, or spontaneous bleeding from your gums—without any injury or known reason.
That happens in a rare condition called Acquired Hemophilia A (AHA). It’s different from Classic Hemophilia as it is not inherited.
Classic Hemophilia A is due to a deficiency of Factor 8.
What Is Classic Hemophilia A?
Hemophilia A was famously known as a “Royal Disease.” It affected multiple members of European royal families in the 19th and early 20th centuries.
This was especially true for the descendants of Queen Victoria of the United Kingdom.
Hemophilia A in Royal Families
- Queen Victoria (1819–1901) is believed to have been a carrier of hemophilia A.
- Three of her daughters were likely carriers, and her gene spread into the royal families of:
- Russia
- Germany
- Spain
Notable Historical Case:
Tsarevich Alexei Romanov, son of Tsar Nicholas II and Tsarina Alexandra (a granddaughter of Queen Victoria), had Hemophilia A.
His illness significantly influenced Russian history. His mother was desperate to heal him. Tsarina Alexandra trusted Grigori Rasputin, a mystic to heal her son. His influence over the royal family helped undermine the monarchy and contributed to the Russian Revolution.
Why Was Rasputin Chosen?
- At the time, there was no treatment for hemophilia.
- Even minor injuries could lead to life-threatening internal bleeding.
- The royal families kept the disease secret, fearing political fallout and a perceived weakness in the line of succession.
Today
- Hemophilia A is still inherited in the same way, but:
- Recombinant factor 8 and gene therapy have greatly improved quality of life.
- Carrier testing and genetic counseling are available for families with a known history.
Acquired Hemophilia A
Acquired Hemophilia A occurs when the immune system mistakenly attacks one of the body’s natural clotting proteins, Factor 8.
Without Factor 8, blood clotting is difficult. Large bruises can form from minor bumps. The lack of clotting can lead to severe, and sometimes life-threatening, bleeding.
Acquired Hemophilia A: Symptoms
In the study, most patients who developed Acquired Hemophilia A (AHA) after COVID-19 vaccination showed classic signs of internal bleeding. These signs often occurred without any injury or warning.
The most often reported signs and symptoms included:
- Hematomas (bruising or deep bleeding under the skin) – found in 35 patients (37%)
- Low hemoglobin levels – a sign of internal blood loss, seen in 26 patients (27%)
- Anemia – reported in 18 patients (19%), indicating reduced oxygen-carrying capacity in the blood
Lab Tests Used to Diagnose Acquired Hemophilia A
1. Anti-Factor VIII Autoantibodies
- These are antibodies that attack clotting factor VIII.
- Found in only 39 cases (41%), showing a significant gap in lab confirmation
2. Factor 8 Activity
- Normally, this clotting protein helps stop bleeding.
- In AHA, levels drop very low.
- Only 45 cases (47%) in the study had this test done.
- Average activity level was just 9.1%, much lower than the normal 50–150% range.
3. Prolonged aPTT (Activated Partial Thromboplastin Time)
- This test checks how long it takes blood to clot.
- A prolonged aPTT suggests something is wrong with the clotting system.
- Reported in only 36 patients (38%)
- Average clotting time: 83 seconds, more than twice the normal range (25–35 seconds)
In recent years, doctors around the world have reported new cases of AHA after COVID-19 vaccination.
These Acquired AHA reports are rare. However, they raised concerns. Researchers have been prompted to ask whether the vaccine could trigger AHA in some people.
To answer this question, Franchini and his group used signal detection analysis. This method identifies unexpected or unusual patterns in large databases of drug or vaccine side effects. It helps scientists spot “signals”—potential safety concerns that need closer investigation.
II. How They Found the Link Between Acquired Hemophilia A and the COVID-19 Vaccine
A systematic case review was made using several major data sources.
1. VigiBase
VigiBase is the largest global database of spontaneous reports of adverse drug reactions (ADRs) and the most comprehensive for adverse events after immunization (AEFIs). It helps detect safety signals for medications and vaccines used worldwide.
2. VAERS (Vaccine Adverse Event Reporting System)
The researchers also searched the VAERS database, which collects reports of adverse events that occur after vaccination in the United States. It is run by the CDC and FDA and serves as a national early warning system for vaccine safety issues.
3. Literature Review
They also reviewed the medical literature to find all published case reports. The review included case series of AHA after COVID-19 vaccination.
4. No Duplicates
To ensure data quality, the researchers carefully examined all identified cases and removed duplicates—including those that appeared in more than one data source (e.g., in both VAERS and published literature). This made the study more reliable.
III. Key Findings
The study gathered and analyzed 95 unique cases of Acquired Hemophilia A (AHA) that occurred after COVID-19 vaccination. Here are the most important takeaways from the data:
Who Was Affected?
- Most patients were older adults:
- 75 patients (79%) were 65 years or older
- Younger women were not affected during pregnancy or after delivery:
- Among women under 65, there were no reports of AHA linked to vaccination during pregnancy or postpartum
- Pre-existing conditions:
- 20 patients (21%) had at least one health condition that is a known risk factor for AHA, like:
- A prior history of AHA
- Cancer
- Autoimmune diseases
- 20 patients (21%) had at least one health condition that is a known risk factor for AHA, like:
Medications Not a Factor
- Some patients were taking other medications but none of the drugs known to cause AHA.
Common Symptoms
The most frequent symptoms when AHA started were:
- Hematomas (deep bruising or bleeding under the skin):
- Reported in 35 patients (37%)
- Low hemoglobin levels (a sign of blood loss):
- Found in 26 patients (27%)
- Anemia:
- Seen in 18 patients (19%)
Lab Findings and Report Quality
- Autoantibodies against factor 8 (the immune system attacking a clotting factor):
- Detected in only 39 cases (41%)
- Low factor 8 activity (a key test for AHA):
- Measured in 45 cases (47%)
- Average clotting activity: 9.1% (very low)
- Prolonged aPTT (a lab test showing delayed clotting):
- Reported in only 36 patients (38%)
- Average aPTT time: 83 seconds (normal is around 25–35 seconds)
Timing and Vaccine Type
- Time from vaccination to diagnosis:
- Median was 18 days
- Most cases happened within 5 to 32 days after vaccination
- This time frame suggests a possible immune reaction set off by the vaccine.
- Type of vaccine:
- 93% (89 cases) were linked to mRNA vaccines (Pfizer-BioNTech or Moderna), which matches their widespread use worldwide
- Vaccine dose:
- In 67 cases (70%), the specific dose number was known
- Most AHA cases occurred after the second dose (30 cases, 40%)
Outcomes
- Data on patient outcomes was available in 71 cases:
- 10 patients (11%) died
- 15 cases (16%) had complete recovery
- 1 case (1%) resolved on its own without treatment—lab values returned to normal after 2 months
IV. Biases and How the Authors Addressed Them
When looking at possible side effects of vaccines, it’s important to ask: Are we seeing a real cause-and-effect relationship—or just a coincidence?
The researchers carefully considered that question and discussed how different types of bias could affect the findings.
Is Acquired Hemophilia A After Vaccines a New Problem?
- Acquired Hemophilia A (AHA) is extremely rare after vaccination of any kind.
- Before COVID-19 vaccines, only three cases of AHA were reported. These were in connection with non-COVID vaccines in the medical literature.
An Increase After COVID-19 Vaccines
- After the first COVID-19 vaccines were authorized emergently and rolled out globally, more cases of AHA started appearing—more than what would normally be expected.
- This pattern was confirmed in the WHO’s VigiBase database, where an unexpected increase in reports of vaccine-related AHA was observed.
But does that increase mean the vaccines caused AHA? The answer isn’t so simple.
Possible Biases That Could Explain the Spike
The authors highlighted two main types of bias that might have influenced the number of reported AHA cases:
1. Detection Bias
- During the pandemic, people who got vaccinated were being closely monitored.
- Doctors were especially alert for rare blood problems after vaccines. One such problem is vaccine-induced immune thrombotic thrombocytopenia (VITT). It was identified in early 2021 after the jab roll-out.
- This extra attention could have led to more testing and more diagnoses of AHA that might have otherwise gone unnoticed.
- In other words, according to the authors, more AHA cases may have been found not because more people were getting AHA but because more people were being checked.
- My take is that testing for Factor 8 is not routine and is not cheap. Before a doctor orders the test, patients tested for it typically have a good reason, like a large bruise that needed explanation. That is why if abnormal levels of Factor 8 are found, they are not coincidence.
2. Notoriety Bias
- After reports of blood clots and other vaccine side effects made global headlines, healthcare providers and patients became more cautious.
- This high level of awareness likely encouraged more reporting of blood-related problems, including AHA—even in cases where the vaccine may not have been the real cause.
- This media attention and regulatory alerts may have increased the perception of risk, even without strong evidence of a direct link.
So—Does the Bias Rule Out a Real Link?
Not necessarily.
The researchers emphasized that even if these biases played a role, they do not rule out the possibility of a true connection between COVID-19 vaccines and AHA.
In fact, the unusual timing of these AHA cases—often occurring within days or weeks of vaccination—makes it worth looking deeper. That’s why they recommend careful, case-by-case clinical reviews to better understand whether vaccines could, in rare cases, trigger AHA.
V. Can COVID-19 Vaccines Cause Acquired Hemophilia A?
The big question is: Did the COVID-19 vaccines actually cause AHA? Or did these cases just happen around the same time by chance? To answer this, scientists look at two key ideas: temporal plausibility and biological plausibility.
1. Temporal Plausibility: Did AHA Happen Soon Enough After Vaccination to Be Related?
Yes, the timing makes sense.
- Whenever a patient seeks a doctor for help, the first question they ask is, “What happened before that?” That is the same when doing a cause and effect study.
- Most cases of AHA were diagnosed more than 5 days after vaccination, with a median of 18 days.
- That time frame is consistent with how long the immune system would take to create antibodies. It takes time to cause symptoms and those symptoms need to be noticed and tested.
- This suggests a possible immune reaction triggered by the vaccine, though timing alone doesn’t prove it.
2. Biological Plausibility: Is There a Mechanism That Makes Sense?
Scientists have looked into how the vaccine might trigger AHA. Here’s what they found:
A. Cross-Reactivity Theory
- One idea was that the Spike protein (used in all COVID-19 vaccines) might accidentally trigger the immune system to attack factor 8 due to structural similarities.
B. T Cell Activation Theory
- A likely explanation involves T cells—a type of white blood cell that helps regulate the immune system.
- Some parts of the Spike protein overlap with highly reactive regions of factor 8.
- These overlapping sequences could activate dormant immune cells in people already prone to AHA.
- Specifically, autoreactive T cell clones—which are usually kept in check—might be triggered by the vaccine to stimulate B cells that make anti-Factor 8 antibodies.
- This immune reaction could then lead to AHA.
The researchers believe this T–cell–based mechanism is plausible, especially when combined with the timing of symptoms after vaccination.
Table: How Vaccine-Associated AHA Differs from Typical AHA
| Feature | Typical AHA | Vaccine-Associated AHA |
|---|---|---|
| Underlying Conditions | ~50% have an underlying cause: autoimmune disease, cancer, pregnancy | Only 21% had known risk factors; 59% had no identifiable cause |
| Drug-induced AHA is rare (<5%) | No pregnancy-related cases; vaccine may act as possible immune trigger | |
| Age Distribution | Most patients are over 65 | 21% were younger than 65 |
| Male-to-female ratio typically balanced | Similar gender ratio, but younger age group more represented | |
| Resolution & Mortality | Mortality rate: 10–20% | Mortality rate: 11% (10 of 96 cases) |
| Spontaneous remission more common in drug-induced AHA | Only 1 case of spontaneous remission | |
| Removing the drug trigger can reverse AHA | Vaccine-related AHA behaves more like primary autoimmune AHA |
Bottom Line
- This study does not prove that COVID-19 vaccines cause AHA. However, it highlights a credible time window. It also identifies a biologically possible immune pathway that could explain the cases.
- The researchers highlight the need for more investigation. They suggest reviewing cases one by one to see if this immune mechanism is at play.
Final Thoughts on Causality
The researchers concluded that while the data cannot prove that COVID-19 vaccines cause AHA, it also does not rule out a causal relationship. The distinct features—lack of traditional triggers, unusual age distribution, and timing after vaccination—make this link worth further investigation.
VI. What This Means for You
Hearing about cases of a rare bleeding disorder after vaccination can be unsettling—but it’s important to put this information into the right context.
1. Acquired Hemophilia A Is Extremely Rare
- Even with the global rollout of COVID-19 vaccines, fewer than 100 unique cases of AHA were identified and confirmed through published reports and safety databases.
- By comparison, billions of vaccine doses have been given worldwide.
- This means the risk is extremely low—far less than 1 case per million doses.
2. Most People Have No Risk Factors
- In this study, most people who developed AHA had no known underlying condition that typically causes the disorder.
- But even in these cases, it’s not certain the vaccine caused AHA—it could still be a coincidence.
- No cases were linked to pregnancy, and no consistent pattern with medications was found.
3. Symptoms to Watch For
If you or someone you know recently received a COVID-19 vaccine, be alert—but not alarmed. Seek medical help if you notice:
- Large, unexplained bruises
- Soft-tissue swelling or deep muscle pain
- Unusual bleeding (gums, urine, joints, etc.)
- Fatigue or weakness from anemia (low blood count)
Early diagnosis and treatment can dramatically improve outcomes.
4. What’s Being Done?
- Researchers, doctors, and public health agencies continue monitoring vaccine safety closely through global databases like VigiBase and national systems like VAERS.
- This ongoing surveillance helps detect rare patterns early and ensure that vaccines remain safe for the public.
Bottom Line
If you’re concerned about vaccine side effects, especially if you have a history of autoimmune disease or abnormal bleeding, talk to your healthcare provider.
Being informed—not fearful—is the best approach.
VII. Summary and Takeaway Points
Acquired Hemophilia A (AHA) is a rare but serious bleeding disorder caused by the immune system attacking a clotting factor in the blood.
Since the start of the global COVID-19 vaccination campaign, a small number of AHA cases have been reported. These cases occurred shortly after vaccination, raising questions about a possible link.
A recent systematic review by Franchini et al. analyzed 96 unique cases from global safety databases (VigiBase, VAERS) and published literature to understand this potential connection better.
Key Takeaways:
- AHA remains extremely rare after COVID-19 vaccination—even with billions of doses administered.
- Most cases occurred in older adults, but about 1 in 5 were under age 65. No cases were reported during pregnancy.
- Over half of the patients had no known risk factors. This is unlike typical AHA cases. In those cases, cancer, autoimmune disease, or childbirth are often involved.
- Symptoms usually began within 18 days of vaccination. This timing is consistent with the time it takes for the immune system to respond.
- A plausible immune mechanism involving T cells may explain how the vaccine could trigger AHA in some susceptible individuals.
- Biases like detection and media attention (notoriety bias) may have contributed to increased reporting, but they do not rule out a possible causal link.
- Most patients recovered with treatment, although 11% died—like known AHA mortality rates. One patient recovered without treatment, which is more typical in drug-induced AHA.
What You Can Do:
- Stay informed about potential but rare side effects.
- Seek medical help for unexplained bruising, bleeding, or weakness after vaccination.
- Talk to your doctor if you have a history of autoimmune disease or bleeding issues before vaccination.
- Don’t panic—the benefits of vaccination continue to outweigh the risks for the vast majority of people.
This study doesn’t give a final answer but raises important questions. Continued research will provide more clarity. Ongoing monitoring will help determine if a rare immune response to COVID-19 vaccines might trigger AHA in very select individuals.
My opinion is that Franchini and his colleagues did a great job in making sure that there is a possibility of a link between the COVID-19 vaccines and Acquired hemophilia A. They did a lot of hard work and even tried to find holes in their study by ruling out biases. Doing so proves that their study is not just some conspiracy theory.
Vaccine related AHA has also been reported after Sinovac-coronavac COVID-19 vaccine.[2]
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References:
- Franchini M, et al. Investigating a Signal of Acquired Hemophilia Associated with COVID-19 Vaccination: A Systematic Case Review. Semin Thromb Hemost. 2023 Feb;49(1):15-26. doi: 10.1055/s-0042-1754389. Epub 2022 Sep 2. PMID: 36055265.
- Bouslama E, Ben Ismail H, Zahra K et al. Case Report: Acquired hemophilia A following COVID-19 vaccine [version 1; peer review: awaiting peer review]. F1000Research 2024, 13:65 (https://doi.org/10.12688/f1000research.128372.1)
Image credits:
- Grigori Rasputin – By Unknown author – [1], Public Domain, https://commons.wikimedia.org/w/index.php?curid=33993658
- Buttock hematoma – By Arlo bosio – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=68352570
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