What are the International Health Regulations and how do they apply to yellow fever?

The International Health Regulations (IHRs) (2005) are a public health measure, designed to protect against and respond to the international spread of disease [1].

Yellow fever (YF) is recognised under the IHRs as a disease with potential for international spread. As a result, some countries require travellers to show proof of vaccination before allowing them to enter that country, to help protect against the introduction and/or spread of the disease. This proof of vaccination is recorded on a document called an International Certificate of Vaccination or Prophylaxis (ICVP), often known as a 'yellow fever certificate'.

Country entry requirements are published on the World Health Organisation (WHO) website. These requirements are subject to change at any time and may be strictly enforced by the authorities in receiving countries.

What is a Medical Letter of Exemption and when can it be issued?

The YF vaccine is not suitable for everyone. Before giving the vaccine, the risks and benefits for each traveller should be considered by a health professional with training and experience in evaluating the benefits and risks of YF vaccination. The decision to vaccinate should be based on an individual risk-benefit assessment, considering the potential for rare but serious adverse events associated with the YF vaccine.

Travellers with a contraindication to YF vaccine

There may be times when an ICVP for YF is required to enter a country, but a health professional advises the traveller should not be vaccinated on medical grounds (see chapter 35 of the 'Green Book') [2]. In these circumstances, travellers should be counselled on the risk of YF disease at the destination and encouraged to consider alternative travel plans. If travel to a YF risk area cannot be avoided or postponed, a Medical Letter of Exemption (MLoE) should be provided (see What else should the traveller know if they are offered a Medical Letter of Exemption?)

Travellers with a precaution to YF vaccine

For those with a precaution to YF vaccine, the risks and benefits of vaccination should be considered carefully and balanced against the risk of YF virus exposure at the destination (see also Should all travellers aged 60 years and over be offered a Medical Letter of Exemption where there is a certificate requirement?).

Any decision to offer vaccination should be based on shared decision-making between the traveller and the health professional working in a Yellow Fever Vaccination Centre (YFVC). Where there is a certificate requirement and the decision is made not to vaccinate a traveller with a precaution to YF vaccine, a MLoE may be issued, at the discretion of the YFVC. The discussion and final decision on whether to offer YF vaccine or a MLoE should be documented clearly in the medical notes.

Should all travellers aged 60 years and over be offered a Medical Letter of Exemption when there is a certificate requirement?

YF vaccination should only be considered for travellers aged 60 years and over if they are visiting areas with current or periodic risk of YF transmission (i.e. where YF vaccination is recommended by WHO) [3]. In this context, age 60 years or over is a precaution for YF vaccination due to an increased risk of YF vaccine associated viscerotropic and neurologic disease in this age group.

As for all travellers with a precaution to YF vaccine, the risks and benefits of YF vaccine should be considered carefully. Where a certificate requirement exists, a MLoE may be appropriate if the risk of vaccine associated adverse events is considered to outweigh the risk of YF disease (see also above: Travellers with a precaution to YF vaccine).

YF vaccine is contraindicated in those aged 60 years or older who are only travelling to areas where YF vaccine is 'generally not recommended' by the WHO (also described as areas with 'low potential for exposure' to YF).

Who can issue a Medical Letter of Exemption?

Health professionals working in designated YFVCs in the UK who have successfully completed NaTHNaC YF training, are the most appropriate individuals to issue a MLoE.

Details of currently designated YFVCs are available on our YFVC Search Locator.

In exceptional circumstances, a health professional supervising the care of an individual, but not working in a YFVC, may provide this documentation.

Do countries have to accept a Medical Letter of Exemption?

Under the IHRs, a MLoE should be taken into consideration by authorities on arrival; however, where there is a certificate requirement, the MLoE is not a guarantee of entry into a country.

Travellers may wish to carry additional documentation relating to their medical condition. They should also consider checking with the embassy of their destination country for any specific documentation requirements before travel.

How do I fill in a Medical Letter of Exemption?

The current ICVP yellow booklets used in the UK have a template for a MLoE. This can be completed and stamped at a designated YFVC. Extra ICVPs can be ordered by contacting Harlow Printing Ltd.

A MLoE can also be written on headed paper of, for example the hospital, clinic or medical centre supervising the traveller's medical care (see example template in Resources section below).

How long is a Medical Letter of Exemption valid for?

The MLoE should be issued on a trip-by-trip basis and should clearly state that it is valid for the current trip only.

What else should the traveller know if they are offered a Medical Letter of Exemption?

The health professional issuing a MLoE must inform the traveller about the risks associated with not being vaccinated, in line with the International Health Regulations (2005) (see Do countries have to accept a Medical Letter of Exemption?). All travellers should be advised about insect bite precautions.

Remember

• Country YF vaccination certificate requirements under International Health Regulations (2005) are in place to protect countries from the introduction and/or spread of YF disease. These requirements may be strictly enforced and are subject to change at any time.
• A YF MLoE should be considered by authorities on arrival, however, it does not guarantee entry into a country.
• Travellers should be made aware of the risks associated with remaining unvaccinated against YF.
• A MLoE is issued at the discretion of the health professional.
• All travellers should be advised about insect bite precautions.
• Health professionals can call the NaTHNaC advice line if they have special risk travellers or travel itineraries they wish to discuss further.

Resources

• WHO International Health Regulations
• Sample Medical Letter of Exemption
• Yellow fever pre-vaccination checklist
• Yellow fever vaccine: Contraindications and precautions reminder