Yellow Fever Vaccine: Travel Requirements & Side Effects Guide

What Is Yellow Fever and Why Is Vaccination Important?

Yellow fever is a potentially fatal viral disease transmitted by infected mosquitoes in tropical regions of Africa and South America. Vaccination is the most effective protection, providing lifelong immunity with a single dose. Approximately 200,000 cases occur annually, with about 30,000 deaths—most of which could be prevented through vaccination.

Yellow fever is caused by the yellow fever virus, a member of the Flavivirus family that also includes dengue, Zika, and West Nile viruses. The disease gets its name from jaundice, a yellowing of the skin and eyes that occurs in severe cases when the virus damages the liver. The virus is transmitted exclusively through the bite of infected Aedes and Haemagogus mosquitoes, which are active during daylight hours.

The disease presents in two phases. The initial acute phase causes fever, muscle pain, headache, loss of appetite, and nausea. Most patients improve after 3-4 days. However, approximately 15-25% of patients enter a more severe toxic phase within 24 hours, characterized by high fever, jaundice, abdominal pain, bleeding, and kidney failure. Half of patients in this phase die within 10-14 days, while the other half recover without significant organ damage.

Yellow fever remains endemic in 47 countries across Africa and Central/South America, putting an estimated 900 million people at risk. Despite the availability of a safe and effective vaccine since 1937, outbreaks continue to occur, particularly in areas with low vaccination coverage. The yellow fever vaccine is one of the most successful vaccines ever developed, with over 99% effectiveness in providing long-lasting protection.

The History of Yellow Fever Vaccination

The yellow fever vaccine was developed in the 1930s by Max Theiler, who was awarded the Nobel Prize in Physiology or Medicine in 1951 for this achievement. The 17D vaccine strain used today is remarkably similar to the original, having been continuously refined while maintaining its excellent safety and efficacy profile. More than 600 million doses have been administered since the vaccine's introduction, making it one of the most extensively studied vaccines in history.

When Do You Need Yellow Fever Vaccination?

Yellow fever vaccination is required for entry to many countries in Africa and South America. Some countries require vaccination for all travelers, while others only require it if arriving from an endemic area. The International Certificate of Vaccination or Prophylaxis (ICVP) becomes valid 10 days after vaccination and is now valid for life.

The decision to get vaccinated against yellow fever depends on your travel destination, your health status, and the specific entry requirements of the countries you plan to visit. The World Health Organization (WHO) categorizes vaccination recommendations into three levels: required for entry, recommended for travelers, and generally not recommended. Understanding these distinctions is crucial for proper travel planning.

Many countries in yellow fever endemic zones require proof of vaccination for entry. This requirement serves dual purposes: protecting the traveler from infection and preventing importation of the virus. Some countries require vaccination only if you are arriving from, or have recently transited through, a country where yellow fever is present. This policy aims to prevent the international spread of the disease while avoiding unnecessary vaccination of travelers from non-endemic regions.

The International Health Regulations (IHR) provide the legal framework for yellow fever vaccination requirements. Under these regulations, countries may require evidence of vaccination as a condition of entry, and this requirement cannot be waived except for documented medical contraindications. It's important to note that individual countries may interpret and apply these regulations differently, and requirements can change based on outbreak situations.

Transit Requirements

Some countries require yellow fever vaccination even for airport transit, defined as spending any time in an airport of an endemic country, regardless of whether you leave the international transit area. This policy reflects the theoretical risk of mosquito bites in airport terminals in endemic regions. Airport transit requirements vary significantly between countries, so travelers should verify current regulations before booking flights with layovers in endemic areas.

Who Should Not Get the Yellow Fever Vaccine?

The yellow fever vaccine should not be given to infants under 6 months, people with severe egg allergy, immunocompromised individuals (including those with HIV with CD4 count below 200), organ transplant recipients, people on high-dose corticosteroids or chemotherapy, and those with thymus disorders. People over 60 years have increased risk of serious side effects and require careful risk-benefit assessment.

While the yellow fever vaccine is remarkably safe for the general population, certain groups face elevated risks and should not receive the vaccine unless the benefits clearly outweigh the risks. The vaccine is a live attenuated virus, meaning it contains a weakened form of the virus that can replicate in the body. This characteristic makes it highly effective but also means it can cause serious disease in people whose immune systems cannot adequately control the attenuated virus.

The most significant contraindication involves severe immunocompromise. This includes people with primary immunodeficiencies, those receiving immunosuppressive therapy (including high-dose corticosteroids, chemotherapy, and biologic agents), organ transplant recipients, and individuals with HIV infection who have CD4 counts below 200 cells/mm³. In these populations, the attenuated vaccine virus can potentially cause a disease similar to wild-type yellow fever, a condition known as yellow fever vaccine-associated viscerotropic disease (YEL-AVD).

Egg allergy represents another important contraindication because the vaccine is produced in chicken eggs and contains residual egg proteins. People with a history of severe allergic reaction (anaphylaxis) to eggs should not receive the vaccine. Those with milder egg allergies may sometimes be safely vaccinated under medical supervision, but this requires careful evaluation by an allergist or immunologist experienced in vaccine reactions.

Age-Related Considerations

Age at both extremes presents special considerations for yellow fever vaccination. Infants under 6 months should never receive the vaccine due to the risk of YEL-AND (yellow fever vaccine-associated neurotropic disease), a rare but serious condition affecting the central nervous system. Infants between 6-8 months should only be vaccinated in exceptional circumstances when travel to high-risk areas is unavoidable and cannot be postponed.

Adults over 60 years face increased risk of both YEL-AVD and YEL-AND. Studies suggest that first-time vaccination in this age group carries a risk of serious adverse events approximately 10-fold higher than in younger adults. For this reason, healthcare providers should carefully weigh the actual risk of yellow fever at the destination against the vaccine-related risks before recommending vaccination for older travelers.

• Infants under 6 months: Absolute contraindication—never vaccinate
• Infants 6-8 months: Only if travel to high-risk area is unavoidable
• Adults over 60: Careful risk-benefit assessment required for first-time vaccination
• Immunocompromised individuals: Contraindicated regardless of age
• Severe egg allergy: Contraindicated; alternative arrangements needed

Medical Exemption Certificates

If you cannot be vaccinated due to medical contraindications, you can obtain a medical exemption certificate (sometimes called a waiver letter). This document, issued by a recognized vaccination center, states that vaccination is contraindicated for medical reasons. While this exemption is internationally recognized under the International Health Regulations, be aware that border officials in some countries may not accept exemption letters or may require additional documentation. In rare cases, travelers with exemptions have been denied entry, quarantined, or vaccinated on arrival.

How Is Yellow Fever Vaccination Administered?

Yellow fever vaccine is given as a single subcutaneous injection, typically in the upper arm. Adults and children over 3 years receive it in the arm, while younger children may receive it in the thigh. The vaccine can only be administered at WHO-authorized yellow fever vaccination centers, and you will receive an International Certificate of Vaccination or Prophylaxis (ICVP) that becomes valid 10 days after vaccination.

The yellow fever vaccine (17D strain) is a live attenuated vaccine that has been used for over 80 years with an excellent safety record. The vaccine is lyophilized (freeze-dried) and must be reconstituted with a diluent immediately before use. After reconstitution, the vaccine must be used within one hour and kept protected from light, as the live virus is sensitive to environmental conditions.

The vaccination is administered by subcutaneous injection—a technique where the needle is inserted at a 45-degree angle into the fatty tissue just beneath the skin. This differs from intramuscular injections, which are given deeper into muscle tissue. The subcutaneous route is preferred for yellow fever vaccine because it optimizes immune response while minimizing adverse reactions.

Before vaccination, the healthcare provider will review your medical history to identify any contraindications or precautions. This includes questions about egg allergy, immune system disorders, current medications (especially immunosuppressants), pregnancy or breastfeeding status, and age. If you are taking immunosuppressive medications, you should bring a list of all your current medications to the appointment.

Vaccination for Different Age Groups

Adults: Adults receive a standard 0.5 mL dose by subcutaneous injection, typically in the outer upper arm (deltoid region). The injection takes only a few seconds. You may be asked to remain at the clinic for 15-30 minutes after vaccination to monitor for any immediate adverse reactions, particularly if this is your first yellow fever vaccination.

Children: Children over 9 months of age who are traveling to endemic areas should be vaccinated. Children under 3 years typically receive the injection in the thigh (anterolateral aspect) because this site has more accessible subcutaneous tissue. The dose is the same as for adults (0.5 mL). Parents should discuss the timing of vaccination with their pediatrician, especially if other routine childhood vaccinations are due.

Children 6-8 months: In exceptional circumstances where travel to a high-risk area cannot be postponed, vaccination may be considered for infants in this age range. This decision requires careful risk assessment by an experienced travel medicine specialist and should only be made when the risk of yellow fever exposure is substantial.

What Are the Side Effects of Yellow Fever Vaccine?

Common side effects include injection site reactions (soreness, redness, swelling), mild fever, headache, and muscle aches, typically appearing 5-7 days after vaccination and resolving within a few days. Serious side effects are rare but include severe allergic reactions (anaphylaxis) and, very rarely, yellow fever vaccine-associated viscerotropic disease (YEL-AVD) or neurologic disease (YEL-AND), occurring in approximately 1 in 250,000 doses.

The yellow fever vaccine has an excellent safety profile, with the vast majority of recipients experiencing no side effects or only mild, self-limiting reactions. Understanding the range of possible reactions helps travelers distinguish between normal vaccine responses and symptoms that warrant medical attention.

Local reactions at the injection site are the most common side effects, occurring in 10-30% of vaccine recipients. These include pain, redness, and swelling at the injection site, typically developing within the first 24-48 hours and resolving spontaneously within a few days. These reactions represent the normal immune response to vaccination and do not indicate a problem with the vaccine or future protection.

Systemic reactions occur in 10-25% of first-time vaccine recipients, typically appearing 5-7 days after vaccination when the attenuated virus is actively replicating and stimulating the immune system. These symptoms include mild fever, headache, muscle aches (myalgia), fatigue, and general malaise. These flu-like symptoms are usually mild and resolve within 1-2 days without treatment. Over-the-counter pain relievers such as paracetamol (acetaminophen) or ibuprofen can be used to manage discomfort.

Rare but Serious Side Effects

While serious adverse events following yellow fever vaccination are rare, travelers should be aware of them:

Anaphylaxis: Severe allergic reactions occur in approximately 1.3 cases per 100,000 doses administered. Symptoms typically develop within minutes to hours after vaccination and may include difficulty breathing, swelling of the throat, rapid heartbeat, dizziness, and widespread hives. Anaphylaxis is a medical emergency requiring immediate treatment with epinephrine. This is why vaccination centers ask you to wait for observation after the injection.

Yellow Fever Vaccine-Associated Neurotropic Disease (YEL-AND): This rare complication involves the central nervous system and can present as encephalitis (brain inflammation), meningoencephalitis, Guillain-Barré syndrome, or acute disseminated encephalomyelitis. YEL-AND occurs at a rate of approximately 0.4-0.8 per 100,000 doses. Most cases occur within 30 days of vaccination, and the majority of affected individuals recover completely, though some may have permanent neurological damage.

Yellow Fever Vaccine-Associated Viscerotropic Disease (YEL-AVD): This is the most serious potential complication, resembling natural yellow fever disease with multi-organ failure. YEL-AVD occurs at a rate of approximately 0.3-0.5 per 100,000 doses but is fatal in approximately 60% of cases. Risk is substantially higher in individuals over 60 years receiving their first vaccination and in those with thymus disorders or immunocompromise.

Can You Get Yellow Fever Vaccine During Pregnancy or Breastfeeding?

Yellow fever vaccination should generally be avoided during pregnancy and breastfeeding. Pregnant women should postpone travel to endemic areas if possible. If travel is unavoidable, vaccination may be considered after careful risk assessment. Breastfeeding mothers should avoid vaccination if their infant is under 6 months, as vaccine virus transmission through breast milk has been documented.

Pregnancy presents a complex situation for yellow fever vaccination decisions. The vaccine contains a live attenuated virus, and there is theoretical concern about fetal infection, though this risk has not been clearly established in clinical studies. Limited data from inadvertent vaccination of pregnant women have not shown increased rates of birth defects or pregnancy complications, but the evidence base is insufficient to confirm safety.

For pregnant travelers, the preferred approach is to postpone travel to yellow fever endemic areas until after delivery. When travel cannot be avoided, the decision to vaccinate should involve careful consideration of the actual risk of yellow fever at the destination, the duration and nature of travel (urban vs. jungle, rainy season, known outbreaks), and the availability of mosquito bite prevention measures.

If vaccination is deemed necessary during pregnancy, it should ideally be delayed until the second or third trimester, as organogenesis (fetal organ development) is complete after the first trimester. However, if travel to a high-risk area is imminent, vaccination may be appropriate even in early pregnancy if the risk of yellow fever is substantial.

Breastfeeding Considerations

Breastfeeding presents specific concerns because the attenuated vaccine virus can be transmitted through breast milk. Cases of YEL-AND have been documented in breastfed infants whose mothers received the vaccine. For this reason:

• Breastfeeding mothers should avoid yellow fever vaccination if their infant is under 6 months old
• If vaccination is essential, consider temporarily suspending breastfeeding for 2 weeks after vaccination
• Alternatively, consider obtaining a medical exemption certificate and relying on strict mosquito bite prevention
• If the infant is over 6 months and at risk of exposure, vaccinating the infant directly is preferred over maternal vaccination

Understanding the International Certificate of Vaccination

After vaccination, you receive an International Certificate of Vaccination or Prophylaxis (ICVP), commonly called the "yellow card." This becomes valid 10 days after vaccination and is now recognized as valid for life. The certificate must be completed by an authorized vaccination center and includes your personal details, vaccination date, and the center's official stamp.

The International Certificate of Vaccination or Prophylaxis is the official document proving yellow fever vaccination status. This standardized form, specified in the International Health Regulations, is recognized by all WHO member states. The certificate is typically a yellow card (hence the common nickname "yellow card") that folds to passport size and should be kept with your passport during international travel.

The certificate includes your full name, date of birth, nationality, date of vaccination, vaccine manufacturer and batch number, signature of the supervising physician, and the official stamp of the vaccination center. All information must be legible and correctly recorded, as errors can lead to problems at border crossings. If your certificate contains any errors, request a corrected version before traveling.

Since 2016, the WHO has recognized that a single dose of yellow fever vaccine provides lifelong protection, and booster doses are no longer routinely recommended. Consequently, the International Health Regulations were amended to specify that the ICVP for yellow fever vaccination is valid for life, eliminating the previous 10-year expiration. However, some countries have been slow to update their entry requirements, and travelers may occasionally encounter border officials requesting evidence of recent vaccination. In such cases, the official WHO position supporting lifelong validity should be helpful.

What If You Lose Your Certificate?

If you have been vaccinated but lost your certificate, contact the vaccination center where you received the vaccine. Authorized centers maintain records for at least 10 years and can issue a replacement certificate. If you cannot remember which center administered your vaccine, or if the center no longer exists, you may need to receive another dose. This is safe and will not cause any problems—repeat vaccination in individuals already immune simply serves as an immune booster.

What to Expect After Vaccination

You may experience mild side effects 5-7 days after vaccination, including low-grade fever, headache, and muscle aches lasting 1-2 days. The injection site may be sore, red, or slightly swollen for a few days. These reactions are normal signs of immune response and don't require medical attention unless severe or prolonged.

Most people feel completely normal after yellow fever vaccination. However, because this is a live vaccine, the attenuated virus replicates in your body to stimulate immune protection. This replication phase typically occurs 5-7 days after vaccination and may produce mild symptoms similar to a very mild viral illness.

Normal post-vaccination experiences include:

• Injection site reactions: Pain, tenderness, redness, or mild swelling at the injection site for 1-3 days
• Low-grade fever: Temperature up to 38.5°C (101°F), typically appearing around day 5-7 and lasting 1-2 days
• Headache: Mild to moderate headache, usually responding well to standard pain relievers
• Muscle aches: Generalized myalgia similar to mild flu symptoms
• Fatigue: Tiredness or general malaise lasting 1-2 days

These symptoms do not indicate that you are infectious or contagious. The attenuated vaccine virus cannot be transmitted to others through casual contact. You can continue your normal activities, including work and exercise, unless you feel unwell. Simple measures such as rest, adequate hydration, and over-the-counter pain relievers (paracetamol or ibuprofen) are usually sufficient to manage any discomfort.

The vaccination site should be kept clean but can be washed normally. There is no need to cover the injection site or avoid getting it wet. Mild bruising at the injection site is occasionally seen and resolves without treatment.

Frequently Asked Questions About Yellow Fever Vaccine