35: Yellow fever
Notifiable

The disease

Yellow fever is an acute flavivirus infection spread by the bite of an infected mosquito. The disease occurs in tropical Africa and South America (see maps on the website of the National Travel Health Network and Centre (NaTHNaC), www.nathnac.org); it has never been reported in Asia despite the presence of the vector. Three epidemiological patterns of yellow fever are recognised – urban, savannah and jungle – although the disease is clinically and aetiologically identical. In urban yellow fever, the viral reservoir is man and the disease is spread between humans primarily by the Aedes aegypti mosquitoes that live and breed in close association with humans. In Africa, an intermediate (savannah) cycle exists that involves transmission of virus from mosquitoes to humans living or working in jungle border areas. In this cycle, the virus can be transmitted from monkey to human or from human to human via mosquitoes. Jungle yellow fever is transmitted among non-human hosts (mainly monkeys) by forest mosquitoes. Humans may become infected when they enter into the forest habitat and can become the source of urban outbreaks. Yellow fever can reappear with outbreaks after long intervals of apparent quiescence. Rural populations are at greatest risk of yellow fever but urban outbreaks do occur in Africa. Urban populations in South and Central America are also at risk due to city centres being re-infested with A.aegypti and increased population movement in to and out of endemic areas.
Yellow fever ranges in severity from non-specific, self-limited symptoms of fever, malaise, photophobia and headache to an illness of sudden onset with fever, vomiting and prostration which may progress to jaundice and haemorrhage. In local populations in endemic areas, the overall fatality ratio is about 5%, rising to 20 to 30% once jaundice and severe symptoms occur. In non-immune travellers and migrants, and during epidemics in areas that have low levels of yellow fever activity, the case fatality rate can exceed 50% (Monath, 2004). The incubation period is generally three to six days but may be longer. Death usually occurs seven to ten days after the onset of illness.
There is no specific treatment for yellow fever. Preventive measures such as the eradication of Aedes mosquitoes, protection from mosquito bites, and immunisation reduce the risk. Jungle yellow fever can only be prevented by Yellow Fever immunisation and personal protection against mosquito bites because of the wide range and distribution of mosquito vectors and mammalian hosts.
There is no risk of transmission in the UK from imported cases since the mosquito vector does not occur in the UK.

History and epidemiology of the disease

Sequence analysis of the viral genome suggests that yellow fever virus originated in Africa about 3000 years ago (Zanotto et al., 1996). However, the earliest record of an epidemic was in the Yucatan in Mexico in 1648. The term ‘yellow fever’ was first used in an outbreak that occurred in Barbados in 1750. The disease became a major problem in the colonial settlements of the Americas and West Africa in the 1700s and was repeatedly introduced into sea ports of the United States and Europe during this time (Monath, 2004).
Transmission of yellow fever by mosquitoes was first postulated by Josiah Clark Nott in 1848 and confirmed by Walter Reed and colleagues in Cuba in 1900. The live, attenuated vaccine that remains in use today was developed in the 1930s. Control of the urban vector, combined with a highly effective vaccine, had reduced human cases, particularly in South America, but there has been a resurgence of the disease in the last decade with at least 200,000 cases estimated to occur annually (Robertson et al., 1996; Monath, 2001).

The yellow fever vaccination

Yellow fever vaccine is a live, attenuated preparation of the 17D strain of yellow fever virus grown in specific pathogen-free embryonated chick eggs. Each 0.5ml dose contains not less than 1000 mouse LD50 units.

Storage

Vaccines should be stored in the original packaging at +2°C to +8°C and protected from light. All vaccines are sensitive to some extent to heat and cold. Heat speeds up the decline in potency of most vaccines, thus reducing their shelf life. Effectiveness cannot be guaranteed for vaccines unless they have been stored at the correct temperature. Freezing may cause increased reactogenicity and loss of potency for some vaccines. It can also cause hairline cracks in the container, leading to contamination of the contents.

Presentation

The yellow fever vaccine is available as a lyophilised powder for reconstitution with a diluent.
Yellow fever vaccines are thiomersal-free. They contain live organisms which have been attenuated (modified).

Dosage and schedule

First dose is 0.5ml of reconstituted vaccine. Further doses should be given at the recommended intervals if required.

Administration

The vaccines should be reconstituted with the diluent supplied by the manufacturer and either used within an hour or discarded.
Doses of 0.5ml of yellow fever vaccine should be given by deep subcutaneous or intramuscular injection irrespective of age.
Yellow fever vaccine can be given at any time in relationship to other inactivated and live vaccines (Public Health England, 2015). However, in the case of co-administration with MMR vaccine there are some data to suggest sub optimal antibody responses against yellow fever, mumps and rubella antigens (Nascimento et al. 2011). Where possible these two vaccines should be given 28 days apart. The vaccines should be given at separate sites, preferably in a different limb. If given in the same limb, they should be given at least 2.5cm apart (American Academy of Pediatrics, 2003). The site at which each vaccine was given should be noted in the patient’s records.

Disposal

Equipment used for vaccination, including used vials, ampoules or syringes, should be disposed of by placing it in a proper, puncture-resistant ‘sharps’ box according to local authority regulations and guidance in Health Technical Memorandum 07-01: Safe management of healthcare waste (Department of Health, 2013).

Recommendations for the use of the vaccine (including re-immunisation)

The objectives of the immunisation programme are to provide a minimum of one dose of yellow fever vaccine for individuals at risk of yellow fever and to prevent the international spread of yellow fever. The latter aims to prevent infected individuals introducing the virus into areas where the presence of mosquito vectors and an appropriate host could support the establishment of yellow fever.
A single dose correctly administered confers immunity in 95 to 100% of recipients. Data suggests that with some exceptions, most vaccine recipients will maintain protective antibody titers for potentially several decades, or possibly life-long, following vaccination (WHO Strategic Advisory Group of Experts (SAGE), 2013).
The following groups should be immunised:
  •  
    laboratory workers handling infected material
  •  
    persons aged nine months or older who are travelling to countries that require an International Certificate of Vaccination or Prophylaxis (ICVP) for entry
  •  
    persons aged nine months or older who are travelling to or living in infected areas or countries in the yellow fever endemic zone (see YF vaccination maps on www.nathnac.org), even if these countries do not require evidence of immunisation on entry.
Immunisation should be performed at least ten days prior to travel to an endemic area to allow protective immunity to develop and for the ICVP (if required) to become valid. However, vaccine should still considered for last minute travellers who should be counselled about the importance of insect bite precautions and possible implications of an invalid ICVP.

Reinforcing immunisation

The WHO Strategic Advisory Group of Experts (SAGE) on Immunization state that (based on currently available data, a single dose of yellow fever vaccine appears to confer life-long protective immunity against yellow fever disease. Therefore, with some exceptions, a booster dose of yellow fever vaccine is not needed to maintain immunity WHO Strategic Advisory Group of Experts (SAGE), 2013).
Reinforcing immunisation should be offered to a small subset of individuals at continued risk who may not have developed long term protection from their initial yellow fever vaccination (see Figure 35.1). This includes those who received their initial yellow fever vaccination:
  •  
    when aged less than two years old
  •  
    during pregnancy
  •  
    whilst infected with HIV
  •  
    when immune suppressed
  •  
    before undergoing a bone marrow transplant
Figure 35.1
 
Reinforcing immunisation
 
*Note time of revaccination should be based on individual assessment of ongoing risk, and may be considered before 10 years assuming there are no contraindications
 
**Please also refer to BHIVA guidance
Figure 35.1
 
Reinforcing immunisation
 
*Note time of revaccination should be based on individual assessment of ongoing risk, and may be considered before 10 years assuming there are no contraindications
 
**Please also refer to BHIVA guidance
In certain situations where there is concern about a traveller’s risk of exposure to yellow fever (e.g. working/living for an extended period in a high risk setting) a booster dose of YF vaccine can be considered – expert advice can be sought from NaTHNaC (www.NaTHNaC.org) or Health Protection Scotland (www.Travax.nhs.uk)
From 11 July 2016 (for all countries), the yellow fever vaccine certificate (ICVP) will be valid for the duration of the life of the person vaccinated. WHO state that a valid certificate, presented by arriving travellers, cannot be rejected on the grounds that more than ten years have passed since the date vaccination became effective as stated on the certificate; and that boosters or revaccination cannot be required (WHO, 2016).

Risk assessment for travel

With the recognition of rare severe adverse events related to yellow fever vaccine (Centers for Disease Control and Prevention (CDC), 2002; Kitchener, 2004), it is critical to make a careful risk assessment prior to administering vaccine. In general, the risk from yellow fever for travel to a yellow fever endemic region outweighs the risk associated with the vaccine (World Health Organization (WHO), 2004). Itineraries should be scrutinised to ensure that the vaccine is given only to those considered at risk from the disease and to those who require an ICVP (see below). In general, the risk of yellow fever from travel to endemic regions of Africa is ten times higher than the risk from travel to South America (Monath, 2004, Monath and Cetron, 2002), but risk depends entirely on itinerary, season of travel and planned activities.
Although the risk is small, infants under nine months are at higher risk of vaccine-associated encephalitis, with the risk being inversely proportional to age. Infants aged six to nine months should only be immunised if the risk of yellow fever during travel is unavoidable; expert opinion should be sought in these situations. Infants aged less than six months should never be immunised (Monath, 2004). Advice on the avoidance of mosquito bites should be given (see contraindications).
Further details about the recommendations for travellers may be found on the NaTHNaC, www.nathnac.org.

International Certificate of Vaccination or Prophylaxis

Under the International Health Regulations 2005, member states may require immunisation against yellow fever as a condition of entry. A valid ICVP is required as evidence. Country requirements are published annually by WHO in International travel and health (available at www.who.int/ith), and on the NaTHNaC country information pages http://travelhealthpro.org.uk/countries.
As of 11 July 2016, The ICVP is valid for the life of the person vaccinated beginning from the tenth day after primary immunisation.

Contraindications

There are very few individuals who cannot receive yellow fever vaccine when it is recommended. When there is doubt, appropriate advice should be sought from a travel health specialist.
The vaccine should not be given to:
  •  
    those aged under six months
  •  
    those who have had a confirmed anaphylactic reaction to a previous dose of yellow fever vaccine
  •  
    those who have had a confirmed anaphylactic reaction to any of the components of the vaccine
  •  
    those who have had a confirmed anaphylactic reaction to egg
  •  
    those who have a thymus disorder
  •  
    patients with primary or acquired immunodeficiency due to a congenital condition, disease process or treatment (see Chapter 6).
Patients with any of the conditions described above who must travel should be informed of the risk of yellow fever and instructed in mosquito avoidance measures. For those who intend to visit countries where an ICVP against yellow fever is required for entry, a letter of exemption should be issued by the Yellow Fever Vaccination Centre or by the practitioner treating the patient. This should be taken into consideration by the port health authorities at the destination.

Precautions

Minor illnesses without fever or systemic upset are not valid reasons to postpone immunisation.
If an individual is acutely unwell, immunisation should be postponed until they have fully recovered. This is to avoid confusing the differential diagnosis of any acute illness by wrongly attributing any sign or symptoms to the adverse effects of the vaccine.

People over 60 years of age

The risk for neurologic and viscerotropic adverse events increases with age (see below). The risk assessment needs to take account of this.

Pregnancy

Yellow fever vaccine should not generally be given to pregnant women because of the theoretical risk of fetal infection from the live virus vaccine. Pregnant women should be advised not to travel to a high-risk area. When travel is unavoidable, the risk from the disease and the theoretical risk from the vaccine have to be assessed on an individual basis. Two studies in which pregnant women have been vaccinated demonstrated no adverse fetal outcomes (Nasidi et al., 1993; Tsai et al., 1993), but transplacental transmission has occurred in early pregnancy (Tsai et al., 1993). WHO state that in areas where yellow fever is endemic, or during outbreaks, the benefits of vaccination are likely to far outweigh the risk of vaccine. Pregnant women should be counselled on the potential benefits and risks of vaccination so that they may make an informed decision (WHO, 2013). Women who continue to be at risk once the pregnancy is completed should be revaccinated.

Breast-feeding

There is some evidence of transmission of live vaccine virus to infants under two months of age from breast milk. For women who are breast-feeding children under the age of nine months expert advice should be sought from NaTHNaC (www.NaTHNaC.org) or Health Protection Scotland (www.Travax.nhs.uk) before administering yellow fever vaccine.

Infants

Although the risk is small, infants under nine months are at higher risk of vaccine-associated encephalitis, with the risk being inversely proportional to age. Infants aged six to nine months should only be immunised if the risk of yellow fever during travel is unavoidable; expert opinion should be sought in these situations. Infants aged less than six months should never be immunised (Monath, 2004). Advice on the avoidance of mosquito bites should be given (see contraindications).

Immunosuppression and HIV infection

Unless the yellow fever risk is unavoidable, asymptomatic HIV-infected persons should not be immunised. There is limited evidence from data, however, that yellow fever vaccine may be given safely to HIV-infected persons with a CD4 count that is greater than 200 and a viral load that is suppressed (Receveur et al., 2000; Tattevin et al., 2004). Specialist advice should be sought in these cases. The antibody response in HIV positive persons may be diminished (Sibailly et al., 1997) (See Chapter 6).
Further guidance is provided by the Royal College of Paediatrics and Child Health (www.rcpch.ac.uk), the British HIV Association guidelines for immunization of HIV-infected adults 2015 (BHIVA, 2015: http://bhiva.org/vaccination-guidelines.aspx) and the Children’s HIV Association of UK and Ireland (CHIVA) Immunisation guidelines (http://www.chiva.org.uk/guidelines/immunisation/).

Adverse reactions

Adverse reactions following yellow fever vaccine are typically mild and consist of headache, myalgia, low grade fever and/or soreness at the injection site and will occur in 10 to 30% of recipients (Monath, 2004; Freestone et al., 1977; Lang et al., 1999; Monath et al., 2002). Injection site reactions tend to occur from days one to five after immunisation. Systemic side effects also occur early but may last up to two weeks (Monath et al., 2002). Up to 1% of individuals may need to alter daily activities. Reactions are more likely to occur in persons who have no prior immunity to yellow fever virus (Monath et al., 2002; Moss-Blundell et al., 1981).
Rash, urticaria, bronchospasm and anaphylaxis occur rarely. In a passive surveillance system in the US, the rate of anaphylaxis following yellow fever vaccine was estimated to be one case per 130,000 doses of vaccine (Kelso et al., 1999). Reactions are most likely related to egg protein in the vaccine. It is possible that some persons are sensitive to and react to the gelatin that is used as a stabiliser in some yellow fever vaccines as well as in other vaccines.
Post-vaccine encephalitis has been recognised as a rare event since the early use of the vaccine. It was particularly seen in infants (see above), and early reports indicated an incidence of 0.5 to 4 cases per 1000 infants under six months of age (Monath, 2004). Since 2001, a new pattern of neurological adverse events was recognised that occurred in older individuals (CDC, 2002; Kitchener, 2004). When this was recognised, a retrospective review revealed other cases that occurred in the 1990s. These events have now been termed yellow fever vaccine- associated neurological disease (YEL-AND). The clinical presentation of this new pattern of neurological events begins four to 23 days following receipt of vaccine with the onset of fever and headache that may progress to include one or more of confusion, focal neurological deficits, coma and Guillain-Barré syndrome. CSF in these cases demonstrates a pleocytosis with increased protein and when, tested, yellow fever virus-specific IgM antibody. The clinical course is usually for complete recovery. All cases have occurred in primary vaccinees who have no underlying yellow fever immunity.
Yellow fever vaccine-associated viscerotropic disease (YEL-AVD) is a newly recognised syndrome of fever and multi-organ failure that resembles severe yellow fever, first described in 2001 (CDC, 2001; Chan et al., 2001; Martin et al., 2001a; Vasconcelos et al., 2001). Two to seven days following vaccination, patients develop fever, malaise, headache and myalgias that progress to hepatitis, hypotension and multi-organ failure; death has occurred in more than 60% of reported cases. Vaccine-derived virus has been isolated from several of the cases and yellow fever viral antigen has been detected in post-mortem samples (Martin et al., 2001a). As with YEL-AND, all cases have occurred in primary vaccinees without underlying yellow fever immunity. In the reports of viscerotropic disease, four out of 23 cases (17%) had had a history of thymus disease with subsequent thymectomy (Barwick Eidex, 2004). Thus, all patients with thymus disorders should not receive vaccine (see Contraindications on p 447).
Based on reported cases and the number of doses of yellow fever vaccine distributed, the US has estimated the risk of neurological disease to be about four cases per million doses and viscerotropic disease to be three cases per million doses (Cetron et al., 2002). These estimates are similar to those made based on cases reported in Europe (Kitchener, 2004). Based on the current evidence, for individuals who are aged 60 years or older, the risk of neurological and viscerotropic adverse events increases several-fold, such that neurological events occur at a rate of about 17 cases per million doses and viscerotropic events at a rate of 20.5 cases per million doses (Martin et al., 2001b; Marfin et al., 2005).
All suspected reactions in children and severe suspected reactions in adults should be reported to the Medicines and Healthcare products Regulatory Agency (MHRA) through the Yellow Card scheme.

Yellow fever vaccination centres

Yellow fever vaccine can only be administered at ‘designated’ yellow fever vaccination centres (YFCVs) as established by the International Health Regulations of WHO.
In England, Wales, and Northern Ireland, the Department of Health, the Welsh Assembly Government, and Department of Health, Social Services and Public Safety, Northern Ireland have devolved responsibility for administering YFVCs to National Travel Health Network and Centre (NaTHNaC) an organisation established in 2003 that is dedicated to providing information to health professionals and setting standards in travel medicine.
A listing of approved YFVCs in England, Wales, and Northern Ireland (EWNI) can be found at: http://nathnacyfzone.org.uk/search-centres
Information on becoming a YFVC in EWNI, including mandatory yellow fever vaccine training clinical information about travel medicine, can be obtained on the NaTHNaC website, at http://nathnac.org/
Practitioners in Scotland should apply to:

Supplies

All vaccines used to protect against yellow fever must be approved by WHO. One WHO-approved licensed vaccine is currently available in the UK – Stamaril™ (Sanofi Pasteur MSD, TelTel 01483 505 515, http://www.sanofi.co.uk
The vaccine is supplied to designated centres only for injection as freeze-dried powder and solvent.
The vaccine is supplied to designated centres only for injection as freeze- dried powder and solvent.

References

American Academy of Pediatrics (2003) Active immunization. In: Pickering LK (ed.) Red Book: 2003 Report of the Committee on Infectious Diseases, 26th edition. Elk Grove Village, IL: American Academy of Pediatrics, p 33.
Barwick Eidex R (2004) History of thymoma and yellow fever vaccination (letter) for the Yellow Fever Vaccine Safety Working Group. Lancet 364: 931. [PubMed]
British HIV Association guidelines for immunization of HIV-infected adults 2008. HIV Medicine (2008), 9, 795–848
CDC (2001) Fever, jaundice, and multiple organ system failure associated with 17D-derived yellow fever vaccination, 1996–2001. MMWR 50: 643–5 [PubMed]
CDC (2002) Adverse events associated with 17D-derived yellow fever vaccination – United States, 2001–2002. MMWR 51: 989–93. [PubMed]
Cetron MS, Marfin AA, Julian KG et al. (2002) Yellow fever vaccine. Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 51 (No. RR-17): 1–10. [PubMed]
Chan RC, Penney DJ, Little D et al. (2001) Hepatitis and death following vaccination with 17D-204 yellow fever vaccine. Lancet 358: 121–2.
Department of Health (2001) Health information for overseas travel, 2nd edition. London: TSO.
Department of Health (2013) Health Technical Memorandum 07-01: Safe management of healthcare waste. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/167976/HTM_07-01_Final.pdf. Accessed December 2013.
Freestone DS, Ferris RD, Weinberg AL and Kelly A (1977) Stabilized 17D strain yellow fever vaccine: dose response studies, clinical reactions and effects on hepatic function. J Biol Stand 5: 181–6. [PubMed]
Kelso JM, Mootrey GT and Tsai TF (1999) Anaphylaxis from yellow fever vaccine. J Allergy Clin Immunol 103: 698–701. [PubMed]
Kengsakul K, Sathirapongsasuti K and Punyagupta S (2002) Fatal myeloencephalitis following yellow fever vaccination in a case with HIV infection. J Med Assoc Thai 85: 131–4. [PubMed]
Kitchener S (2004) Viscerotropic and neurotropic disease following vaccination with the 17D yellow fever vaccine, ARILVAX((R)). Vaccine 22: 2103–5. [PubMed]
Lang J, Zuckerman J, Clarke P et al. (1999) Comparison of the immunogenicity and safety of two 17D yellow fever vaccines. Am J Trop Med Hyg 60: 1045–50. [PubMed]
Marfin AA, Eidex RS, Kozarsky PE and Cetron MS (2005) Yellow fever and Japanese encephalitis vaccines: indications and complications. Infect Dis Clin North Am 19(1): 151–68. [PubMed]
Martin M, Tsai TF, Cropp B et al. (2001a) Fever and multisystem organ failure associated with 17D-204 yellow fever vaccination: a report of four cases. Lancet 358: 98–104.
Martin M, Weld LH, Tsai TF et al. (2001b) Advanced age a risk factor for illness temporally associated with yellow fever vaccination. Emerg Infect Dis 7: 945–51.
Monath TP (2001) Yellow fever: an update. Lancet Infect Dis 1: 11–20. [PubMed]
Monath TP (2004) Yellow fever vaccine. In: Plotkin SA and Orenstien WA (eds) Vaccines, 4th edition Philadelphia: WA Saunders Company, pp 1095–176.
Monath TP and Cetron MS (2002) Prevention of yellow fever in persons travelling to the tropics. Clin Infect Dis 34: 1369–78. [PubMed]
Monath TP, Nichols R, Archambault WT et al. (2002) Comparative safety and immunogenicity of two yellow fever 17D vaccines (ARILVAX and YF-VAX) in a phase III multicenter, double-blind clinical trial. Am J Trop Med Hyg 66: 533–41. [PubMed]
Moss-Blundell AJ, Bernstein S, Shepherd WM et al. (1981) A clinical study of stabilized 17D strain live attenuated yellow fever vaccine. J Biol Stand 9: 445–52. [PubMed]
Nascimento Silva JR Camacho LA, Siqueira MM, et al. (2011) Mutual interference on the immune response to yellow fever vaccine and a combined vaccine against measles, mumps and rubella. Vaccine. 29:6327–34 [PubMed]
Nasidi A, Monath TP, Vandenberg J et al. (1993) Yellow fever vaccination and pregnancy: a four-year prospective study. Trans R Soc Trop Med Hyg 87: 337–9. [PubMed]
Public Health England (2015) Revised recommendations for administering more than one live vaccine, 24 April 2015, PHE publications gateway number: 2015015.
Receveur MC, Thiebaut R, Vedy S et al. (2000) Yellow fever vaccination of human immunodeficiency virus-infected patients: report of two cases. Clin Infect Dis 31: E7–8. [PubMed]
Robertson SE, Hull BP, Tomori O et al. (1996) Yellow fever. A decade of re-emergence. JAMA 276: 1157–62. [PubMed]
Sibailly TS, Wiktor SZ, Tsai TF et al. (1997) Poor antibody response to yellow fever vaccination in children infected with Human Immunodeficiency Virus Type 1. Pediatr Infect Dis J 16: 1177–9. [PubMed]
Tattevin P, Depatureaux AG, Chapplain JM et al>. (2004) Yellow fever vaccine is safe and effective in HIV-infected patients. AIDS 18: 825–7. [PubMed]
Tsai TF, Paul R, Lynberg MC and Letson GW (1993) Congenital yellow fever virus infection after immunization in pregnancy. J Infect Dis 168: 1520–3. [PubMed]
Vasconcelos PF, Luna EJ, Galler R et al. (2001) Serious adverse events associated with yellow fever 17DD vaccine in Brazil: a report of two cases. Lancet 358: 91–7. [PubMed]
World Health Organization (2013) Vaccines and vaccination against yellow fever WHO Position Paper –June 2013, Weekly Epidemiological Record, 5 July, No. 27, 88, 269–284
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Figure 35.1
 
Reinforcing immunisation
 
*Note time of revaccination should be based on individual assessment of ongoing risk, and may be considered before 10 years assuming there are no contraindications
 
**Please also refer to BHIVA guidance
Figure 35.1
 
Reinforcing immunisation
 
*Note time of revaccination should be based on individual assessment of ongoing risk, and may be considered before 10 years assuming there are no contraindications
 
**Please also refer to BHIVA guidance
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