One of the most common questions that we are asked by our patients is whether or not they are still covered by their previous vaccines. This is not as straightforward a question as there are a number of factors which always need to be taken into account when trying to advise if suitable cover is still in place.
This information must not be used in place of a detailed medical consultation with one of our staff members and is only provided to give general guidelines.
I understand & accept the limitations
of the information given regarding the duration of vaccine cover
How vaccines work
There are different types of vaccines used to protect the international traveller. They may be given in different ways (orally or by injection, given once or on a number of occasions etc) but generally all work by ‘training’ the body’s immune system to produce protective antibodies against a specific disease. This can be described as a ‘priming course’ where the body is exposed to a specific vaccine and in doing so learns how to create the necessary protective antibodies for that specific disease in case of future exposure.
Some vaccines are extremely efficient and give excellent cover to almost everybody who receives them (eg Yellow Fever vaccine ~ 99%) whereas others provide more limited cover (eg Typhoid ~ 60% to 80%). Just because you have received a complete vaccine course does not necessarily mean that you have achieved full cover so this always needs to be borne in mind.
Also various international authorities (eg WHO, CDC etc) may also assign different durations against the cover provided by a certain vaccine which can lead to great confusion. For instance the US authorities state that the intramuscular version of Typhoid vaccine provides cover for 2 years whereas the European authorities have opted for a 3 year cover duration.
In cases where a vaccine course has not been completed, or the recommended schedule has not been followed, the level of cover may vary quite significantly from what would normally be expected. To get the individuals immune system correctly ‘trained’ may require that further doses (more than the usual recommended number) are given to get the immune memory sufficiently ‘primed’ so it can respond in case of future exposure.
The information below purely seeks to give you an overview of the vaccine duration question relating to the most commonly used ones within our practice. Please understand that this is purely an overview and does not seek to answer every possible variation which may occur within the cover for any individual. The individuals personal immune status, previous surgery or medications they are taking may significantly influence their personal response to any individual vaccine.
The current vaccine used against Yellow Fever in Europe is called STAMARIL. The International Health Regulation [IHR] body met in July 2016 to agree that, in the majority of situations, the vaccine provides life-long cover after a single full injection. However it may take some time for this information to filter down through the layers of government officials and border guards before it is accepted internationally without exception. On that basis some patients may be recommended to have their original vaccination ‘revalidated’ to confirm their cover and lessen the possibility of issues arising at border check points.
NOTE: There is a growing level of international concern that this ‘life-long’ cover may in fact not be correct in certain individual circumstances (eg when the vaccine was given during pregnancy, in a child under 2 years of age, in an immunocompromised individual, after bone marrow transplant etc) and so this long duration of cover does need to be considered on an individual basis.
Poliomyelitis / Tetanus / Diphtheria / Pertussis
There are a number of vaccines used in adults which provide cover against these diseases. The most commonly used ones are REVAXIS (which covers against Polio, Tetanus and Diphtheria and may be written in the WHO yellow vaccination book as TdIPV) and DIFTAVAX or DiTe (which provides cover against Tetanus and Diphtheria and written in the yellow book as Td). In an individual who has received a full initial priming vaccine course (usually given at birth since approximately 1945) then a single dose is all that is required to provide cover. However in those individuals where there is no clear history of having ever received a full vaccination course they may be encouraged to have the vaccine on three occasions. Once the priming course has been given then only a single injection every 10 years is recommended for the international traveller.
There are also two other Tetanus-containing vaccines used in Ireland at present;
- BOOSTRIX (provides cover against Tetanus, Diphtheria and Pertussis – often written as TdaP)
- BOOSTRIX IPV (provides cover against Tetanus, Diphtheria, Pertussis and also Poliomyelitis – may be written as TdaP_IPV)
The cover against Polio, Tetanus and Diphtheria is as above (usually boosted every 10 years) but in the case of Pertussis the cover is more questionable. Many authorities (including the Irish ones) would accept that the Pertussis cover lessens quite quickly (within a year) and so may encourage reissuing this vaccine on a much more regular basis if there is a specific risk of exposure.
The most commonly used vaccines against Typhoid are called TYPHIM Vi and TYPHERIX. Following a single vaccine (by injection) it is known that these vaccines provide approximately 60% to 80% cover against this disease and that the cover falls after about a two year period. This is why the US authorities usually recommend boosting this vaccine every 2 years. In Europe the cover is thought to be sufficient for up to 3 years. It is for this reason that within TMB we would regularly encourage our patients to have this vaccine before a trip even though they may officially have a further 3 to 6 months of cover remaining (based on European guidelines).
The two most commonly used single vaccines against Hepatitis A are AVAXIM and HAVRIX. The initial priming course for both of these vaccines requires them to be given on two occasions. The normal recommendation is that these two doses should be given approx. 6 to 12 months apart. However internationally it is well accepted that actually it is possible to separate the initial and the second completion dose by up to 10 years (approx.) and that following this it is still expected that the individual should have cover for at least 25 years (probably longer).
The two most commonly used single vaccines used against Hepatitis B are HB VAX PRO and ENGERIX. The normal primary course is to administer the vaccine on three occasions over a 6 month period. In some cases, where cover is needed more quickly, a rapid schedule can be used. This requires that the vaccine is given on three occasions over approximately one month and then a 4th dose in 12 months time. This final dose can be given some time later and should still suitably complete this initial course but if the gap between the 3rd and the 4th dose is considered excessive then some groups may recommend that the individual should have two further doses rather than the single one which was initially scheduled. Once a completed course has been achieved (either using the standard three dose regime or the rapid 4 dose regime) then ideally the individual should have a blood test a month or two later to check that they have achieved a sufficient level of protective antibodies. This basically shows that the body’s immune system has been ‘primed’ and ready to produce protective antibodies should the need arise in the future following exposure. In the case of Hepatitis B the body’s immune system is excellent in that once an individual shows a sufficient level of antibody production it is accepted that they should not require any further vaccination cover against this disease.
There are a number of combined vaccines where cover against two or more diseases is included within the same administration. However the cover provided against the individual components may vary considerably and so the information below is just provided to give some guidance as to what would usually be recommended.
TWINRIX provides cover against both Hepatitis A & Hepatitis B. The vaccine is usually scheduled along the same protocol as used for Hepatitis B vaccines as indicated above in that a routine (3 dose) or rapid (4 dose) regime can be used. Once a course has been completed the cover against Hepatitis A is usually excellent and last for approximately 25 years. The Hepatitis B cover should be confirmed with a blood test designed to show that a suitable level of antibody production has been achieved.
VIATIM / HEPATYRIX are both combined Hepatitis A and Typhoid vaccines. Following a single dose of either of these vaccines the cover against Typhoid is thought to last for between 2 to 3 years (see Typhoid section above) and the cover for Hepatitis A needs to be completed with a further dose at approximately 12 months (see Hepatitis A section above)
There are and have been a number of Rabies vaccines used in Ireland over the past decades. These are frequently written into the WHO yellow vaccination book as VERORAB or HDCV or RABIPUR. In all cases these vaccines are given on either 3 or 4 occasions to provide the initial ‘priming’ cover against this disease. The usual initial course is given on three occasions over one month followed by a further ‘booster’ at about 12 months. If the standard schedule has not been followed correctly then the individual may be recommended to have more doses to try and ensure that suitable ‘training’ of the immune system has been achieved.
The way this vaccine works is that by providing the vaccine on a number of occasions the individual’s immune system basically ‘learns’ how to produce the protective antibodies so that if they are exposed to risk in the future the required protective antibodies can be very rapidly created. Unfortunately this immune memory is not anywhere as efficient as what is provided for other vaccines (see Hepatitis B section above) and so it is essential that after any possible exposure the individual urgently seeks further vaccination (typically on two occasions if a full initial course has been given) to get protective antibodies circulating to help protect against this deadly disease.
This immune ‘amnesia’ (where the body’s ability to rapidly remember how to produce the necessary antibodies is lost) varies from individual to individual and that is why all international authorities recommend that, even though you may have had the initial vaccines very recently, you should always seek further vaccines following any and every potential exposure.
The most commonly used vaccines against the bacterial form of Meningitis (Meningococcal) are usually written in the WHO yellow vaccination book as either ACYW-135 or NIMENRIX. Over the past few years (since September 2012) we have mainly used NIMENRIX and this is thought to provide cover in most situations for between 3 to 5 years. In fact the duration of cover could even be longer as this is what is known as a ‘conjugate’ vaccine and similar to the one used for many years in the childhood vaccine programme. However in certain situations (eg entrance to the Hajj in Saudi Arabia) the duration of the vaccine is set much shorter and so a further dose may be required for entrance formalities to obtain a visa.
The current vaccine against this disease is called IXIARO. This vaccine is currently given by injection on two occasions about a month apart and then a further dose is given at 12 months (approx.) to complete the initial priming course. The length of duration provided by this 3 dose course remains uncertain so a single booster dose (for those at continued risk) is usually recommended every 3 years.
The oral vaccine DUKORAL is taken on two occasions between 1 to 6 weeks apart before travelling to a region where there is an expected risk. The duration of cover is thought to last approximately 2 years and a single booster dose at that stage should cover for a similar duration. If there has been a gap of more than 2 years since the initial course was completed then two further doses (1 to 6 weeks apart) may be recommended. This vaccine also provides cover against one of the most common causes of traveller’s diarrhoea – E coli. However the duration of this cover is much shorter than what is provided against Cholera. It is thought that cover against E coli may only last for 3 to 4 months and so in many patients a single dose of DUKORAL is often recommended before travel even though this may be within the 2 year cover provided against Cholera.
Tick Borne Encephalitis (TBE)
The current vaccination against TBE is called TICOVAC. The vaccine is given by injection on two occasions (usually 1 month apart but can be shortened if necessary due to expected exposure) and then completed with a further single dose at 12 months. If the initial two dose regime has not been completed with the 3rd dose and a patient returns to obtain protection some years later then a further two dose course may be recommended.
The vaccine against Influenza is usually given by a single injection each year as the WHO and other international experts seek to change the vaccine constituents to cover the expected strains which will circulate in both Northern and Southern Hemispheres. Ideally the vaccine should be given during the months of September or October each year.