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"I was recently faced with the dilemma of whether or not to give a yellow fever vaccine to an older patient (an 83 year old fit man) going to West Africa, an area with significant risk of yellow fever. From what I could gather there was a "difficult to quantify" risk of death from either giving or not giving the vaccine. In the end I advised the man not to have the vaccine and to take rigorous bite avoidance precautions (which I think is probably the standard advice in a man of this age). Was this the best decision based on the evidence?
I suspect this dilemma will be encountered with increasing frequency as retirees travel to destinations such as The Gambia in search of winter sun. When considering vaccination of travellers who are aged 60 years and older, it is essential to determine whether they will be at risk for yellow fever at their destination, and whether vaccination is required under International Health Regulations.
Since the mid 1990's reports of severe neurological and viscerotropic adverse reactions following primary yellow fever vaccination have been reported, particularly in the over 60 age group, the risk increasing with age (Kitchener 2004 and Khromava et al 2005).
Yellow fever vaccine-associated neurological disease (YEL-AND) typically begins 4-27 days following vaccination with the onset of fever, headache and confusion, and may include coma, focal neurological deficits or Guillain-Barré syndrome. All cases have occurred in primary vaccinees and most make a complete recovery. (Martin et al 2001)
Yellow fever vaccine-associated viscerotropic disease (YEL-AVD) resembles severe yellow fever and is characterised by fever, malaise, headache and multi-organ failure developing within 2-7 days of vaccination. All cases have occurred in primary vaccinees, but in contrast to YEL-AND, the mortality rate is over 60%. (Chan et al 2001 and Kitchener 2004)
It is critical that practitioners make a careful risk assessment prior to administering the vaccine. They need to discuss with their patient the risk of serious illness or death from contracting yellow fever versus the risk of the vaccine. In general, the WHO advises that the "risk from yellow fever for travel to a yellow fever endemic region outweighs the risk associated with the vaccine", but because of recent reports of death in unvaccinated travellers and the risk of severe adverse events following vaccination, doctors should be careful to administer the vaccine only to persons truly at risk of exposure to yellow fever.
The absolute risks have been estimated as follows:
Overall risk for Serious AEFI  ³16 cases per million doses (rising to ³53 cases per million doses in the over 60 age group. NNH = 21,780 (95% CI 12,382 - 48,170)
Risk for YEL-AND is reported as ³3-5 cases per million doses rising to ³14-25 cases per million doses in the over 60 age group; 16 cases worldwide since 1992.
NNH =70,608 (95% CI 27,458 - 657,452)
Risk for YEL-AVD is reported as ³3-5 cases per million doses rising to ³18-25 cases per million doses in over 60 age group; 36 cases worldwide since 1996.
NNH = 65,340 (95% CI 25, 556 - 4,917,845) (Cetron et al 2002; Kitchener 2004; Martin et al 2001 & Khromava et al 2005)
Therefore, the risk of YEL-AND and YEL-AVD in the over 60 age group increases by a factor of 5-6 or a rate of about one case per 40,000 doses of yellow fever vaccine administered.
The CDC, Atlanta has estimated the risk of illness and death during the peak risk period (July-October) in an unvaccinated traveller to West Africa for a 2-week stay as 50 per 100,000 and 10 per 100,000, respectively. The risks of illness and death are 10x greater in West Africa compared to South America. In non-immune travellers, the case mortality can exceed 50% (Monath 2004) and indeed of the 6 cases reported among travellers from the US and Europe in 1996-2002, ALL were fatal.
Therefore, in relative terms, the risk of severe illness and death from contracting yellow fever is 20x and 4x greater respectively, than the risk of severe neurological and viscerotropic adverse reactions following primary yellow fever vaccination in the elderly.
Elderly travellers who have previously been vaccinated for yellow fever, but who require a booster can be reassured that these serious reactions have only been reported in primary vaccinees without any underlying yellow fever immunity.
Providing they do not have a medical contraindication (e.g. egg allergy or history of thymus disorders), the elderly can be administered the vaccine with minimal risk. It should also be borne in mind when visiting a country where an International Certificate of Vaccination or Prophylaxis (ICVP) is a requirement for entry, should the traveller decide against vaccination, it is likely that they would be denied entry even with a letter of medical exemption. The only acceptable contraindications to vaccination are medical conditions, rather than risk aversion. Such travellers should be advised to reconsider their travel plans and choose an alternative destination.
It is advisable that travellers are vaccinated at least a month before departure, allowing early recognition and treatment of any adverse reactions whilst still in the UK.
In this particular case, Prof Avery advised his patient not to have the vaccine and to take mosquito avoidance measures. I wonder whether the decision would have been different if they had been able to base it on the absolute and relative risks of vaccination?
In conclusion, the current evidence suggests that elderly travellers to yellow fever endemic areas should be offered vaccination as this carries a lower risk of morbidity and mortality than travelling unvaccinated.
Information resources for the GP and useful downloadable PILs
Yellow fever vaccination in persons aged 60 years and older
Yellow Fever Vaccine - Information for Travellers factsheet
Insect Bite Avoidance Travellers Factsheet
Immunisation against infectious disease - 'The Green Book'