Yellow fever is an acute illness caused by a flavivirus transmitted only by Aedes mosquitoes in tropical Africa and Latin America. Person-to-person spread does not occur. Ninety percent of cases of yellow fever occur in Africa, with the global total being approximately 200,000 cases of yellow fever each year, of which approximately 30,000 are fatal.1 In its early stages, yellow fever presents as a non-specific febrile illness which may be confused with other common infections of the tropics. The acute phase is characterised by fever, shivers, myalgia, anorexia, nausea and vomiting: infection may begin to resolve in three to four days following this stage. Approximately 20% of infections progress to a severe, haemorrhagic form of the disease, ‘classical yellow fever’ which is fatal in 20% of people thus affected.2 No specific therapeutic agents are available for treatment of yellow fever and supportive treatment is indicated. Vaccination is the most effective preventive measure against yellow fever, with a single dose conferring life-long immunity within 30 days, with no need for a booster dose. In the absence of vaccination, mosquito bite avoidance should be practiced. Indeed, in areas where yellow fever occurs, mosquito bite avoidance is good practice regardless of vaccination status as other mosquito borne infections such as chikungunya and dengue (for which there are no vaccines) are likely to be present.
Under usual circumstances, yellow fever is the only disease for which an International Certificate of Vaccination or Prophylaxis (ICVP)3 may be required for entry into a defined list of countries under the International Health Regulations.4 The current international certificate requirement for polio vaccine in some countries is a temporary measure only. The ICVP for yellow fever must be signed and stamped by an appropriate person and is valid only when a WHO-approved vaccine has been administered. In May 2014, the WHO World Health Assembly adopted an amendment to Annex 7 of the IHR, stipulating that term of validity of the ICVP will change from 10 years to the duration of the life of the person vaccinated.5 Until June 2016, current IHR text on yellow fever vaccination and certificates will apply: some countries may still require proof of vaccination or boosting within the last 10 years.
The United Kingdom (UK) as a signatory to the IHR is required to designate specific yellow fever vaccination centres (YFVCs) ‘in order to ensure the quality and safety of the procedures and materials employed’.4
The statutory responsibility for designating YFVCs in Scotland lies with Health Protection Scotland (HPS), having been passed from the Scottish Government in December 2006. Through a programme of registration, training, and audit, HPS seeks to assure overall standards and consistency of practice within YFVCs in Scotland. This ensures that Scotland meets UK obligations under the IHR as well as contributing to protecting the health of travellers from Scotland.
Designated YFVCs in Scotland are required to keep appropriate records of all yellow fever vaccine they administer for a period of 10 years, submitting complete reports of vaccine utilisation and any adverse events to HPS on an annual basis. This report covers the eighth year of returns to HPS for the period 1 January to 31 December 2014.
Methods and analysis
In 2014, 241 YFVCs were registered with HPS, compared with 238 in 2013. All 241 YFVCs submitted a return on the number of doses of vaccine administered in the calendar year 2014 (RR 100%). The data were collated within a web-based database. For the purpose of this analysis, data were extracted and analysed using Microsoft Excel. NHS board area population data for 2013 were obtained from the National Records of Scotland.6
Yellow fever vaccination centres in Scotland in 2014
Of the 241 vaccination centres nearly half (48%) were in Greater Glasgow & Clyde, Lothian and Grampian NHS Boards: 59(24%), 42(17%), and 40(17%), respectively (Figure 1). Shetland, Orkney, and Western Isles NHS Boards contributed the smallest number of centres at 2 (1%), 2 (1%) and 1 (<1%) respectively.
In terms of YFVCs per 100000 population, there were 5/100000 for the whole of Scotland in 2014. By NHS board (Figure 2), Orkney, Western Isles, Grampian and Highland had the highest numbers per 100000 population at 9/100000, 7/100000, 7/100000 and 6/100000, respectively. Lanarkshire (2/100000) and Ayrshire & Arran (2/100000) had the lowest numbers of centres per 100000 population.
Doses of YFV administered in YFVCs in Scotland in 2014
In 2014, the 241 YFVCs administered 10364 doses of yellow fever vaccine, an increase of 3% from 2013 (N=11193) and a reduction of 21% from 2009 (13084) when returns first began being collated. The number of doses administered per centre across Scotland ranged from 0 to 904 (mean + standard error = 43+7). 73% (175/241) of the centres administered between 1 and 50 doses (Figure 3), with 11% (27/241) administering no doses, and 4% (9/241) administering over 300 doses.
The NHS board areas delivering the greatest number of doses (Figure 4) were Grampian (2850 doses, 27% of total), Lothian (2270, 22%) and Greater Glasgow & Clyde (2751, 26%). Shetland (60, 1%) Western Isles (42, <1%) and Orkney (40, <1%) administered the lowest number of doses.
Mandatory vaccination against yellow fever aims to prevent country-to-country spread of disease, and is often applied to vulnerable countries without yellow fever disease but where the mosquito vector and monkey potential host are present. The current yellow fever vaccine has been available for 70 years, being derived from seed lots in turn derived from a 17D strain developed in the 1940s7, 8.
The yellow fever vaccine recommended by WHO is safe and effective,9 with a single dose sufficient to confer life-long immunity against yellow fever in the great majority of people vaccinated.10 However, it is important to carry out a risk assessment for each traveller as there may be circumstances where revaccination may be indicated.
Serious adverse events are rare: among these are allergic complications and yellow fever virus-associated neurotropic disease (YEL-AND). This is a rare but serious adverse event estimated to occur at a rate of 0.4-0.8 cases/100,000 doses, although that rate was higher in those aged over 60 years.9 Another low incidence but serious adverse event is yellow fever virus-associated viscerotropic disease (YEL-AVD). This condition closely resembles naturally-acquired yellow fever in terms of clinical features and viral proliferation in the body of the affected person.11 YEL-AVD has an estimated incidence of 0.3-0.4 cases/100,000 doses being higher in those with a history of thymus disease and, like YEL-AND, higher in older aged people.8
It should be noted that the threshold for reporting adverse events may vary between countries. It may not always be possible to precisely identify yellow fever vaccine as the cause of an adverse event, particularly where other vaccines have been delivered simultaneously.
Before giving any vaccine, the health professional should carry out a risk assessment considering not only the risk of the vaccine preventable disease, but also the risk associated with the intervention. The likelihood of the traveller being infected with yellow fever virus via the bite of an infected mosquito must be weighed against the chance of yellow fever vaccination resulting in an adverse event. In Scotland, biennial on-line training as well as face-to-face training and email correspondence ensure that YFVCs are kept up-to-date with developing trends and any pertinent WHO recommendations.
Where there is a certificate requirement but YFV is contraindicated or the risk of adverse reaction is considered greater than that of the disease, an exemption certificate may be considered. The risk remains, however, that the destination country may not recognise such certificates.12
All designated centres agree to adhere to a ‘Code of Practice’ which stipulates standards to be met in relation to safety, training, record keeping and reporting, particularly of adverse events.
Since being tasked with overseeing the designation of YFVCs, HPS has established a Yellow Fever Programme, to facilitate registration, training, monitoring and audit of centres in Scotland, consistent with that for England, Wales and Northern Ireland.
In conclusion, designated YFVCs in Scotland continue to comply with conditions of registration. It is hoped that the audit process will lead to continued improvements in both knowledge and practice.
Further detail on the Scottish Yellow Fever Programme can be found on the HPS website (http://www.hps.scot.nhs.uk/yellowfever/index.aspx). This includes how to apply for designation as a YFVC in Scotland; downloadable application and information pack; and a list of resources for centres. There is also a YFVC locator function which allows individuals, including members of the public, to search for their nearest YFVCs across Scotland, and view the services on offer.
HPS would like to thank the yellow fever vaccination centres (YFVCs) throughout Scotland who have co-operated with and supported the implementation of the Yellow Fever Programme (YFP).
- WHO. Yellow fever. Factsheet no. 100. Updated March 2014. Available from: http://www.who.int/mediacentre/factsheets/fs100/en/. (accessed 5 November 2015).
- Paessler S and Walker DH. Pathogenesis of the viral hemorrhagic fevers. Annual Review of Pathology: Mechanisms of Disease. 2013;8:411-440. Available from: http://www.annualreviews.org/doi/pdf/10.1146/annurev-pathol-020712-164041. (accessed 5 November 2015).
- WHO. International certificate of vaccination or prophylaxis. Available from: http://www.who.int/ihr/ports_airports/icvp/en/. (accessed 5 November 2015).
- WHO. International Health Regulations 2005. Second ed. Geneva: World Health Organization, 2005. Available from: http://www.who.int/entity/ihr/publications/9789241596664/en/index.html. (accessed 5 November 2015).
- WHO. World – Yellow fever vaccination booster (International travel and health update). 2015. Available from: http://www.who.int/ith/updates/20140605/en/. (accessed 5 November 2015).
- National Records of Scotland. NHS board population estimates 2014. Available from: http://www.nrscotland.gov.uk/statistics-and-data/statistics/statistics-by-theme/population/population-estimates/mid-year-population-estimates. (accessed 5 November 2015).
- Barnett E. Yellow fever: epidemiology and prevention. Clinical Infectious Diseases. 2007;44(6):850-6. Available from: http://cid.oxfordjournals.org/content/44/6/850.long. (accessed 5 November 2015).
- Staples JE, Gersham M, Fischer M. Yellow fever vaccine: Recommendations of the Advisory Committee on Immunizations Practices (ACIP). Morbidity and Mortality Weekly Report. 2010;59(RR07):1-27. Available from: http://www.cdc.gov/mmwr/indrr_2010.html. (accessed 5 November 2015).
- PAHO. Control of yellow fever: field guide. Scientific and Technical Publications No 603. Washington DC: PAHO, 2005. Available from: http://www.paho.org/hq/index.php?option=com_docman&task=doc_download&Itemid=270&gid=20159&lang=en. (accessed 5 November 2015).
- WHO. Meeting of the Strategic Advisory Group of Experts on Immunization, April 2013 – conclusions and recommendations. Weekly Epidemiological Record.2013;88:201-216. Available from: http://www.who.int/entity/wer/2013/wer8820.pdf?ua=1. (accessed 5 November 2015).
- Pulendran B, Miller J, Querec TD and Akondy R. Case of yellow fever vaccine-associated viscerotropic disease with prolonged viremia, robust adaptive immune responses, and polymorphisms in CCR5 and RANTES genes. Journal of Infectious Diseases. 2008;198(4):500-507. Available from: http://jid.oxfordjournals.org/content/198/4/500.full. (accessed 5 November 2015).
- Hardiman M, Wilder-Smith A. The revised International Health Regulations and their relevance to travel medicine. Journal of Travel Medicine. 2007;14(3):141-144. Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1708-8305.2007.00117.x/pdf. (accessed 5 November 2015).