Whooping cough (also known as “pertussis”) represents a serious and contagious infection caused by the bacterium bordetella pertussis. The disease is particularly dangerous to babies and young children, surveys show that one out of every 200 infected babies will not survive. Immunization by vaccination is considered to be the most effective way to reduce the risk of a pertussis infection.
Characteristics of the pertussis vaccine
Since the pathogen is of the same origin, the pharmaceutical form of the pertussis vaccine consists of a combination vaccine against the infectious diseases diphtheria, tetanus and pertussis. This vaccine combination is licensed under the code “Dpt” and includes antibacterial toxoids serving as an agent to kill the pertussis-causing pathogen. At present, no licensed monovalent vaccine against pertussis is available. Later versions of the vaccine are of acellular consistence in order to reduce the danger of febrile reactions caused by patient´s immune defense. Acellular vaccines contain only those parts of the pathogen, which evoke the necessary immune reaction. In the year 2005 a version of the vaccine has been licensed under the code “Tdap”, containing the tetanus and diphtheria toxoids in combination with the acellular version of pertussis vaccine. This first pertussis-containing vaccine offered the option of a single-dose immunization, making it possible to vaccinate adolescents and adults against pertussis.
The estimated efficacy of the acellular pertussis vaccine to prevent a pertussis infection range between 84% and 85%. Despite the fact that – in comparison to the whole cell version – the efficacy of accellular vaccine diminishes faster, at least 3 protective antigens were determined, being of higher or similar efficacy than the cellular vaccine. Nevertheless, predictions of 10 years protection against pertussis had recently to be revised downward, latest medical researches show a duration of effective prevention against a whooping cough infection of 5 to 8 years. Persons already contracted with whooping cough can act on the assumption of being protected for 4 to 20 years.
The danger of waned immunity
Despite comprehensive childhood pertussis vaccination campaigns, the pathogen has succeeded in persisting among vaccinated population. The recent recurrence of pertussis infections result mainly from two facts.
First, the declining efficacy of the pertussis vaccination caused by pathogen´s development of vaccine resistance and secondly the appearance of new mutation strategies of the Bordetella pertussis bacterium, prevalent vaccines cannot cope with. Therefore whooping cough has resurged and is nowadays becoming one of the most common vaccine-preventable diseases in the western hemisphere. Significant changes on population of the pathogen back the perception, that the bacterium has recently developed sophisticated adapting and mutating activities to abide in vaccinated environment. These changes include growth and increased complexity of antigenic substances in order to differ from prevalent vaccine strains. Another surviving strategy of the pathogen is the increased production of internal toxic substances with a higher toxic level. This approach of rising antigenic variety is able to derogate the efficacy of the pertussis vaccine, together with an increased concentration of pathogen´s toxin it represents an increased suppression on body´s defenses. These mutations of bordetella pertussis will challenge medical research programs in order to find appropriate responses to that threat. Solutions are supposed to show an integrated approach to that problem by improving significant characteristics of the vaccine, reducing pathogen´s reproduction ability and providing interaction between body´s immune system and the effectiveness of pertussis vaccine.
Acute reactions at the injection site such as redness and swelling of skin as well as soreness and tenderness are considered to be a normal answer of body´s immune system. Although determination of more rare adverse reactions – like allergic responses or extensive limb swelling- is difficult unless meaningful data can be obtained, the administration of a non cellular pertussis vaccine can be regarded as an appropriate way to mild local adverse reactions. Since clinical trials usually do not involve pregnant women, significant research results of possible side effects on this group of patients are hardly available. Generally, side effects for vaccinated persons differ for infants and adults/adolescents. Very prevalent reactions of vaccinated babies are pain, redness and swelling at the injection site as well as increased crying and irritability, sometimes going hand in hand with being off-colored and having a short-term fever. Vaccine experiences such as loss of appetite, diarrhea and vomiting are also not uncommon. Responses like febrile convulsions, floppiness, high fever or severe allergic reactions can be found in very rare cases and are strictly subject to intense medical surveillance. In addition to relevant facts like vaccine dose and infant´s age, the reaction pattern depends also on infant´s nutrition and individual psychological circumstances.
Since protection through vaccination is likely to wane while growing up, adolescents and adults are supposed to get vaccinated again. Disobeying of this fact has lead to a recent recurrence of pertussis infections among adult population. As far as side effects of administration to adults are concerned, only light reactions like a sore arm for about one day and a mild fever have been determined.
Pertussis vaccination is strictly contraindicated for persons with a proven allergic reaction to any components of the vaccine. Due to the importance of pertussis vaccination, persons with a history of allergic responses to vaccine components are supposed to see an allergist to determine whether the reaction can be desensitized to grant a safe receive of the vaccination. In addition, pertussis vaccine is contraindicated for adolescents with a history of encephalopathy. Administration of the cellular version (Tdp) can sometimes moderate certain adverse reactions among this group of patients. The possible role of pertussis vaccines in causing neurologic reactions or deterioration of basic neurological data as well as the assumption, that the neurological status after vaccination might differ from the situation previously evaluated has lead to recommendations to reschedule pertussis vaccination in case of infants with neurological diseases.
Administration in pregnancy
At any rate, immunization against pertussis should be a part of the pre-pregnancy planning and is subject to be adjusted with the attending physician. Since significant data on consequences of administration during pregnancy are still insufficient, recommendations turn out to be divergent. In the U.S. pregnancy is not considered to represent a contraindication for an acellular pertussis vaccine treatment but in most European countries vaccination during pregnancy is not recommended and in case of necessity due to medical reasons strictly subject to thoroughly medical surveillance. In the UK the giving of pertussis vaccine is regarded to be without risk between the 28. and the 38. week of pregnancy. Generally, in terms of risk and benefit, it is considered to be safer to receive the vaccination than to expose the newborn baby to the risk of catching whooping cough. Even if the mother is already vaccinated, her baby will still need to receive the vaccine later on according to the normal vaccination schedule for infants.
Immunization by vaccination is considered to be the best and most effective way to reduce the risk of a pertussis infection. Although in some cases – like administration in pregnancy or vaccination of infants with instable neurological status – preventive measures have to take place, it can be stated that – in terms of risk and benefit – a pertussis vaccination represents the safer option in comparison to the consequences of catching whooping cough.