Vaccines Recommended for all Adults

Tetanus and Diphtheria Vaccine

Regular booster immunizations against tetanus and diphtheria throughout life using a combined vaccine are recommended in many countries [91]. Clostridium tetani is found ubiquitously in soil and infection occurs mainly through contaminated wounds, whereas Corynebacterium diphtheria is transmitted via droplets. Despite a low incidence rate in Europe with 161 cases of tetanus and 36 cases of diphtheria per year (mean from 2009 to 2014) [92], vaccination against these diseases is still of importance. Due to the mode of transmission, vaccination does not decrease the prevalence of the pathogen, and there is no herd immunity effect for tetanus. Every individual needs to be vaccinated in order to be protected. A large outbreak of diphtheria in the former Soviet Union in the early 1990s with more than 140,000 cases clearly demonstrated that the pathogen is still present and can spread rapidly in a partially unprotected population [93]. For one of our studies a cohort of persons above the age of 60 was recruited in Austria in order to receive a booster shot against tetanus and diphtheria. Efforts to retrieve information about vaccination history were only partially successful, as it was not possible to determine the exact time point of the last vaccination in 10 % and 53 % of the cases for tetanus or diphtheria, respectively [94]. Similar data are available from France and Belgium [95, 96]. Appropriate vaccination documentation is crucial to deliver booster vaccinations at the right time points. Vaccination against tetanus is recommended when wounds which could potentially be contaminated with soil (e.g. after accidents) are treated and no recent vaccination is documented. Official recommendations specify the use of a combined tetanus/diphtheria vaccine in such cases in order to avoid multiple tetanus shots and a lack of diphtheria vaccination, but in the past single tetanus vaccinations were common. In the above-mentioned study only 31 % of the participants had received their last tetanus/diphtheria vaccination as a combined vaccine [94].

Several studies have demonstrated that tetanus- and diphtheria-specific antibody concentrations are frequently below levels considered to be protective for adults, and particularly for the old [95-98]. In an Austrian cohort 12 % and 65 % of persons older than 60 years were not protected against tetanus or diphtheria, respectively [94]. The elapsed time since the last vaccination, as well as age, has an impact on antibody titers against tetanus. At all time points antibody concentrations are lower in the old compared to young adults and are negatively correlated with the elapsed time since the last vaccination [99]. Upon booster vaccination antibody concentrations increase in most older persons, but approximately 10 % do not develop sufficient antibody levels against diphtheria after a single booster shot [94]. This cohort was followed for 5 years after the booster shot and we showed that at this time point again, 10 % and 45 % of the participants were not protected against tetanus or diphtheria, respectively. A second booster shot was administered, as Austrian vaccine recommendations include shortened tetanus and diphtheria booster intervals of 5 years for persons over the age of 60. Similar to the first booster all participants developed protective antibody concentrations against tetanus, but 6 % again did not respond to the diphtheria vaccine [94]. In conclusion, single-booster shots later in life do not elicit sufficient and long-lasting antibody responses in a substantial portion of the old.

Due to the poor vaccination documentation for many older adults, it is difficult to reliably assess correct primary vaccination in childhood and the number of booster shots administered throughout life. A study in France showed that the number of vaccine doses received in life decreases with age. Young adults (<30 years) received on average 7.1 doses (95 % CI 6.9-7.2) doses of tetanus vaccine, which corresponds well with recommendations of five doses during childhood/adolescence and 10 year-booster intervals afterwards. However, persons aged 50-60 years received only 5.7 (95 % CI 4.6-6.8) doses over their life-time, indicating a lack of regular booster vaccinations [95]. Vaccination strategies for the future should include regular and well-documented booster shots throughout life, as post-booster antibody concentrations correlate with pre-booster antibody concentrations [98]. The success of primary vaccination late in life for persons without adequate priming remains to be elucidated, as the problem of memory generation late in life is well documented in animal models [100]. Considerations about improved vaccines, particularly for diphtheria, should also be taken into account.

 
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