Sarah Bennett
The yellow fever vaccine has been a source of controversy due to the risk of adverse events, including severe allergies, serious neurological problems, organ failure, and even death in rare cases. While the vaccine is generally safe and effective, with over 500-600 million doses administered worldwide, resulting in protective antibodies in 99% of recipients within 30 days, there have been reports of serious adverse events, particularly in individuals with compromised immune systems and young children. The duration of protection after primary vaccination is also a subject of controversy, with some evidence suggesting that immunity may be shorter in immunocompromised individuals. To minimize the risk of adverse events, healthcare professionals should only vaccinate individuals at risk of yellow fever exposure and carefully consider contraindications and precautions.
| Characteristics | Values |
|---|---|
| Effectiveness of the vaccine | The 17D yellow fever vaccine has been one of the most effective vaccines available since its development in 1937. |
| Safety | The yellow fever vaccine is generally safe, including for people with asymptomatic HIV infections. Mild side effects may include headache, muscle pains, fever, and rash. However, there is a small risk of severe allergic reactions, neurological problems, and organ failure. |
| Contraindications | The vaccine is contraindicated for infants under six months old, people with thymus disorders, people with primary immunodeficiencies, and those with severely compromised immune systems. |
| Adverse events | There have been reports of serious adverse events (SAEs) such as vaccine-associated visceral disease and encephalitis. The risk of SAEs may be higher in certain populations, such as the elderly and infants. |
| Duration of protection | There is controversy over the duration of protection provided by the vaccine, with some arguing that protection may be lifelong, while others suggest the need for revaccination. |
| Manufacturers | As of 2013, there were four WHO-qualified manufacturers: Bio-Manguinhos in Brazil, Institute Pasteur in Senegal, the Chumakov Institute in Russia, and Sanofi Pasteur in France and the United States. |
| Travel requirements | Some countries require a yellow fever vaccination certificate for entry, depending on the risk of yellow fever transmission in the traveller's country of origin. |
| Underreporting | Underreporting of cases is a concern, with WHO estimating the true number of cases to be 10 to 250 times higher than reported. |
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What You'll Learn
Yellow fever vaccine safety in organ-transplanted patients
The yellow fever vaccine has been considered one of the most effective vaccines available since its development in 1937. It is on the World Health Organization's List of Essential Medicines. The vaccine is made from a weakened yellow fever virus. While the vaccine is generally safe, there are some rare cases of adverse reactions and life-threatening side effects, especially in individuals with compromised immune systems.
There have been some concerns about the safety of the yellow fever vaccine in organ-transplanted patients. A 2023 investigation reported the first known transmission of the live, attenuated yellow fever vaccine virus through solid organ transplantation to four recipients, resulting in severe neurological disease and two deaths. The source of infection in the organ donor was traced back to a blood transfusion from a recently vaccinated donor. This incident highlights the potential risk of transmitting live vaccine virus strains through blood transfusions and organ transplants.
However, it is important to note that data on adverse events among organ-transplanted patients who received the yellow fever vaccine are scarce. A multicenter study in Brazil reported 19 cases of organ-transplanted patients who inadvertently received the yellow fever vaccine, with only one patient experiencing a slight reaction at the injection site. No other significant side effects were observed in this cohort.
While the yellow fever vaccine is generally contraindicated in immunocompromised patients, including organ transplant recipients, some studies suggest that it may be safe for this population under certain conditions. For example, a case report described a 62-year-old patient who received an allogeneic bone marrow transplant nine years before his uneventful immunization with the yellow fever vaccine.
In conclusion, while there have been rare cases of severe adverse events associated with the yellow fever vaccine in organ-transplanted patients, the current evidence is limited and further research is needed to comprehensively assess the safety of the vaccine in this specific population. Healthcare workers should exercise caution and carefully evaluate the risks and benefits for each individual patient before administering the yellow fever vaccine to organ-transplanted patients.
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Rare cases of severe adverse events
The yellow fever vaccine is considered safe, with over 500 million doses administered and very few documented cases of vaccine-associated illness. However, there have been rare but serious adverse events following the vaccination.
One rare adverse event is an allergic reaction with difficulty breathing or swallowing, known as anaphylaxis. This occurs in about eight cases per million doses. Another rare adverse event is swelling of the brain, spinal cord, or surrounding tissues, called encephalitis or meningitis. Encephalitis was once considered a risk only for children under six months, but cases have been identified in older children and adults. Meningoencephalitis, a combination of encephalitis and meningitis, has also been observed in older children and adults.
Yellow fever vaccine-associated acute viscerotropic disease (YEL-AVD) is another rare but severe adverse event. It causes a severe disease closely resembling yellow fever caused by virulent strains of the virus. The clinical picture includes visceral dissemination of the YFV 17D virus, with high lethality. As of January 2019, there have been 62 confirmed cases and 35 deaths from YEL-AVD. One underlying risk factor for YEL-AVD is thymectomy, and old age may also be a factor, although evidence is conflicting.
Yellow fever vaccine-associated acute neurotropic disease (YEL-AND) is a rare neurological complication. Serious neurological problems occur in about four cases per million doses. The risk of neurologic disease and encephalitis is higher in individuals with compromised immune systems and very young children.
There have been reports of rare adverse events in elderly patients receiving the yellow fever vaccine, with some studies showing adverse events while others show benefits. Precaution and case-by-case decision-making are advised for this population. The same precautions are warranted for infants aged 6-8 months, with the vaccine contraindicated in those under 6 months and safe after 9 months.
In conclusion, while the yellow fever vaccine is generally safe and effective, there is a small risk of rare but severe adverse events, including anaphylaxis, YEL-AVD, YEL-AND, encephalitis, meningitis, and meningoencephalitis. These events are very rare, and the vaccine remains the best way to avoid yellow fever, a disease of high lethality.
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Yellow fever vaccination entry requirements for certain countries
The yellow fever vaccine has been one of the most effective vaccines available since its development in 1937. It is on the World Health Organization's List of Essential Medicines. The vaccine is made from a weakened yellow fever virus. It is considered safe, with over 500 million doses given and very few documented cases of vaccine-associated illness. Mild side effects may include headache, muscle pains, pain at the injection site, fever, and rash.
Some countries require a yellow fever vaccination certificate for entry. This depends on whether the country being travelled to has been designated by the World Health Organization as a 'country with a risk of yellow fever transmission'. In a few countries, all travellers must be vaccinated against yellow fever, regardless of where they are arriving from. Exemptions are usually made for newborn children. Countries that require vaccination include Peru, Brazil, Nigeria, the Democratic Republic of Congo, Republic of Congo, Central African Republic, Kenya, and Angola.
There are some contraindications and precautions to consider. The vaccine should not be given to those with very poor immune function, including those with a history of thymectomy, and those taking immunosuppressant drugs. It should also be avoided by people with thymus disorders associated with abnormal immune cell function, and people with primary immunodeficiencies. The vaccine is considered safe in pregnancy and breastfeeding, and for those with HIV infection but without symptoms. However, there is a small risk of severe adverse reactions, including severe allergies, serious neurological problems, organ failure, and even death.
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Yellow fever vaccination in people with HIV
The yellow fever vaccine is generally considered safe for people with HIV. However, there are some important considerations and potential risks associated with its administration in this population. Firstly, it is crucial to distinguish between asymptomatic HIV-positive individuals and those with severe HIV infection or AIDS. While the vaccine is contraindicated in people with severe immunodeficiencies, including those with advanced HIV infection and AIDS, it is recommended for HIV-infected people who are asymptomatic and have a CD4+ T cell count of at least 200 cells per ml. This recommendation is supported by data on the immunogenicity and safety of the yellow fever vaccine among HIV-infected individuals with CD4+ T-cell counts above this threshold.
Several studies have reported on the safety and efficacy of the yellow fever vaccine in people living with HIV. The majority of these studies have shown that the vaccine is safe and effective in this population, with only mild adverse events reported in some cases. For example, one retrospective study evaluated the immunogenicity and tolerability of the vaccine in 23 French HIV patients, with only one patient experiencing mild adverse events and no serious adverse events (SAEs). Another study in Kenya found that fractional doses of the yellow fever vaccine can be safely used in HIV-infected individuals, further supporting the evidence-based guidelines for this group.
However, there have been rare cases of severe adverse events and even fatalities associated with the yellow fever vaccine in people with HIV. For instance, a 53-year-old man with undiagnosed HIV infection and a low CD4+ count of 108 cells/µL developed fatal yellow fever vaccine-associated acute neurotropic disease (YEL-AND) after vaccination. Another case reported a 53-year-old HIV patient with a similar CD4+ count who presented with myeloencephalitis after vaccination and died. These cases highlight the importance of careful evaluation and monitoring of individuals with HIV before and after administering the yellow fever vaccine.
Overall, while the yellow fever vaccine is generally considered safe for asymptomatic HIV-positive individuals with adequate CD4+ T-cell counts, further research is needed to fully understand the safety and efficacy of the vaccine in this population, especially those with lower CD4+ T-cell counts or advanced HIV infection. Additionally, strengthening the systems for detecting and investigating serious adverse events during vaccination campaigns is crucial to enhance the safety profile of the vaccine in this vulnerable group.
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Yellow fever vaccination in pregnant or nursing people
The yellow fever vaccine is generally considered safe, with over 500 million doses administered and very few documented cases of vaccine-associated illness. The vaccine is made from a weakened yellow fever virus and has been used since 1938. It is on the World Health Organization's List of Essential Medicines.
However, live vaccines, including the yellow fever vaccine, are generally not recommended during pregnancy due to the theoretical risk of strain reversion and congenital infection following gestational exposure. Unvaccinated pregnant women are advised to avoid travelling to yellow fever-endemic areas and handling potentially infected material. If travel or contact is unavoidable, vaccination during pregnancy should be considered on a case-by-case basis.
Studies have shown that the yellow fever vaccine can be given to pregnant women without any adverse effects on their pregnancy. However, pregnancy can lower a woman's ability to respond to vaccines, and there may be an increased risk of a reaction to the yellow fever vaccine during pregnancy. Additionally, the gestational stage at vaccination can affect seroconversion, with women vaccinated in the third trimester potentially having lower antibody levels and being more susceptible to infection.
If a pregnant woman is at high risk of catching yellow fever, vaccination may be offered as it is the best way to prevent this life-threatening illness. The benefits of vaccination in this case are believed to outweigh any risks. No extra monitoring is required following yellow fever vaccination during pregnancy, and the baby is very likely to be born healthy.
While there is limited information available specifically about nursing and the yellow fever vaccine, it is important to note that the vaccine is safe for people with immunosuppressive diseases and those undergoing immunomodulatory or immunosuppressive therapy. Therefore, it is likely safe for nursing people as well, but individual cases may vary, and consultation with a healthcare provider is advised.
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Frequently asked questions
The yellow fever vaccine is generally considered safe, with over 500 million doses given and very few documented cases of vaccine-associated illness. Mild side effects may include headache, muscle pains, fever, and rash. However, there is a small risk of more severe adverse events, including severe allergies, serious neurological problems, organ failure, and even death.
The yellow fever vaccine is not recommended for individuals with very poor immune function, such as those with primary immunodeficiencies or those taking immunosuppressant drugs. It is also contraindicated in infants between zero and six months and people with thymus disorders. Pregnant women and individuals with egg allergies should consult their physicians before receiving the vaccine.
The World Health Organization (WHO) has stated that a booster dose of the yellow fever vaccine is not necessary, as immunity does not decrease with time. However, certain populations, such as pregnant patients and stem cell transplant recipients, may still require a booster dose. Travelers to high-risk areas who received their last dose ≥10 years ago should also consider a booster.
