New strategies: How vaccines can be made even better
The global campaigns for the oral polio vaccine, shown here in India, demonstrate how successful active immunization can be. With consistent vaccination, polio could be eradicated. This has already been achieved with smallpox. / © Imago/Hindustan Times
Since 1980, smallpox has been eradicated worldwide through a concerted vaccination campaign. A similar goal has almost been achieved for poliomyelitis. The number of cases of infection with tetanus or diphtheria bacteria, or with measles, mumps, rubella, and chickenpox viruses, has declined dramatically in Germany thanks to the vaccinations recommended by the German Standing Committee on Vaccination (STIKO). And vaccination against human papillomaviruses and hepatitis B viruses can significantly reduce the risk of developing cervical or hepatocellular carcinoma. So, all is well? A closer look reveals some challenges.
Vaccinations are only successful if the immune system is functioning well, but this isn't always the case.
When a baby is born, its complement system is not yet fully developed, and the cells of the innate immune system, such as natural killer cells or macrophages, are not yet functional. Although T and B lymphocytes respond to antigens, B cells are primarily activated (Th2 response), and the antibodies produced have low affinity and a short lifespan (1).
Newborns are therefore extremely vulnerable to pathogens. Their immune systems are not sufficiently functional to deal with vaccines containing attenuated pathogens.
It receives nest protection from its mother. / © Adobe Stock/FotoSabine
The fact that newborns do not die prematurely from infections despite their incompletely developed immune systems is due to the protective barrier: During pregnancy and during breastfeeding, babies receive IgG and IgA antibodies via the placenta and breast milk. This protects the infant from pathogens with which the mother has already been exposed.
To take advantage of this protective effect, a pregnant woman is recommended to be vaccinated against diphtheria, tetanus, pertussis, and influenza between the 27th and 34th weeks of pregnancy. The Abrysvo® vaccine against respiratory syncytial virus (RSV) infection can also be administered between the 24th and 36th weeks of pregnancy; however, this maternal immunization is not currently recommended by the STIKO.
Studies have shown that the protection provided by this so-called borrowed immunity lasts for up to six months in newborns, which bridges the particularly vulnerable period of the infant.
To date, this type of infection prevention has been used little because there is always the fear that problems during pregnancy or damage to the fetus may occur, which are linked—justifiably or not—to the vaccination (2).
Many vaccines for seniors contain adjuvants or a higher dose of antigen to ensure an adequate immune response. / © Adobe Stock/Klaus Eppele
As we grow and mature, the immune system matures. However, immunosuppression can occur for various reasons. Certain genetic predispositions, infections with influenza or the Epstein-Barr virus, medications and diseases, as well as malnutrition or chronic stress, can have a greater or lesser impact on the functioning of the immune system. Affected individuals are more likely to suffer from simple infections and should not receive live vaccines.
Over the course of life, the body's cells generally age, which also affects the immune system. The shrinkage of the thymus has a particularly serious impact on the immune response. The thymus is responsible for the differentiation and maturation of T lymphocytes and begins to lose size and functionality starting during puberty, resulting in a gradual decline in the number of naive T cells. The number of naive B lymphocytes also decreases. Instead, antigen-experienced memory cells increase, some of which are already somewhat "depleted."
Overall, lymphopenia develops with age, and the body can no longer respond adequately to new antigens and malignant cells. Therefore, the risk of developing a tumor increases from around the age of 70. At the same time, the immune system no longer responds well to vaccines, and the protection provided by active immunization diminishes (1).
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