Live attenuated vaccines

Live vaccines contain attenuated, i.e. virulently weakened pathogens that are still capable of reproducing. As a rule, however, these cannot trigger the disease. Their great advantage is that they produce a real disease in "miniature", so to speak, without symptoms, and therefore achieve a good and long-lasting immunity. They can induce local immunity and general immunity.

Mumps, measles, rubella, varicella, live herpes zoster vaccine, rotavirus, influenza (nasal), yellow fever, typhoid (oral).

No longer regularly performed: smallpox, polio (oral vaccination according to Sabin) , tuberculosis (BCG)

Live vaccines are generally more effective than inactivated vaccines, as they induce not only humoral immunity (by means of circulating antibodies) but also a cellular immune response (which can last up to a lifetime). In general, the vaccines are highly attenuated against the actual pathogens by eliminating some virulence factors. Thus, the response to the vaccine is usually bland. Occasionally, however, the reaction is symptomatic, especially if there is a congenital or acquired immune deficiency. A disadvantage is that the vaccine protection is only available after a time in which the body's own immune system has reacted.

Many live vaccines are injected. Although they prevent the respective disease, they usually do not prevent the pathogen from initially entering the organism (e.g. via the mucous membranes). In this case, no symptoms of the disease develop. The pathogen also disappears from the organism after some time. However, infectivity may persist in the meantime. Vaccines that are applied via the mucous membranes, such as the flu vaccine for children and adolescents, can induce vaccination protection already at the entry site of the pathogens and thus prevent infection. Transmission is prevented.

Vaccinations with a live vaccine, such as against rubella, measles-mumps-rubella or varicella, should be avoided during pregnancy. However, accidental vaccination with measles-mumps-rubella, rubella or varicella vaccine during or shortly before pregnancy does not lead to termination of pregnancy according to national and international recommendations.

A disadvantage of live vaccines is that they can cause more severe side effects, as the living pathogens can still be pathogenic despite restrictions.

Live vaccines in risk groups: For risk groups, the risk of becoming seriously ill is greater due to insufficient attenuation of the virulence of the pathogen. In the case of underlying diseases such as immunodeficiency, for example, vaccination with the live influenza vaccine is contraindicated according to the STIKO - due to illness or as a result of immunosuppressive therapy. Also in certain diseases such as severe asthma is warned against the use.

The genetic changes in attenuated vaccine pathogens usually occur spontaneously after multiple passages under certain conditions. In principle, genetically modified pathogens can also be used in which gene segments have been deliberately eliminated or which have received foreign gene segments through recombination.

Until 1998, a live vaccine was used as an oral vaccination against poliomyelitis in Germany. In the meantime, only vaccine with killed pathogens is administered. Thanks to their help, polio cases have been reduced by 99 percent worldwide since 1988. This vaccination carries minimal risks. For example, vaccine-associated paralytic poliomyelitis (VAPP) can occur. The incidence of these paralytic cases is one to two cases per million initial vaccinations.

1. Hof H (2019) Active immunization. In: Hof H, Schlüter D, Dörries R, eds Duale Reihe Medizinische Mikrobiologie. 7th, completely revised and expanded edition. Stuttgart: Thieme p.743
2. Minor PD (2015) Live attenuated vaccines: historical successes and current challenges. Virology 479-480:379-392.