As precaution, LAVs tend not to be administered during pregnancy. However, the actual potential for fetal damage remains theoritical. For example, numerous studies have demonstrated that accidental rubella vaccination during pregnancy did not result in an increased risk of birth defects
LAVs can have increased potential for immunization errors:
Some LAVs come in lyophilized (powder) form. They must be reconstituted with a specific diluent before administration, which carries the potential for programmatic errors if the wrong diluent or a drug is used.
Many LAVs require strict attention to the cold chain for the vaccine to be active and are subject to programme failure when this is not adhered to.
Since LAVs contain living organisms, there is a degree of unpredictability raising some safety and stability concerns.
Attenuated pathogens have the very rare potential to revert to a pathogenic form and cause disease in vaccines or their contacts. Example for this are very rare, serious adverse events of:
Vaccine-associated paralytic poliomyelitis (VAPP) and
Disease-causing vaccine-derived poliovirus associated with oral polio vaccine (OPV)
Functional immune systems eliminate attenuated pathogens in their immune response. Individuals with compromised immune systems, such as HIV-infected patients may not be able to respond adequately to the attenuated antigens.
Sustained infection, for example tuberculosis (BCG) vaccination can result in local lymphadenitis or a disseminated infection
If the vaccine is grown in a contaminated tissue culture it can be contaminated by other viruses (e.g. retrovirus with measles vaccine)
LAVs stimulate an excellent immune response that is nearly as good as compared to an infection with the wild-type-pathogen. Live microorganisms provide continual antigenic stimulation giving sufficient time for memory cell production. In the case of viruses or intracellular microoranisms where cell-mediated immunity is usually desired, attenuated pathogens are capable of replicating within host cells.
Available since the 1950s, live attenuated vaccines (LAV) are derived from disease-causing pathogens (virus or bacteria) that have been weakened under laboratory conditions. They will grow in a vaccinated individual, but because they are weak, they will cause no or very mild disease.
There are many types of vaccines. Different types or formulations affect how they are used, how they are stored, and how they are administered. If they are to be safe and effective, it is vital to be familiar with the different types and to know how to handle them. Different vaccines can cause different adverse reactions, and it is important to recognize what these may be.
Some of the antigens above can be combined in a single injection that can prevent different diseases or that protect against multiple strains of infectious agents causing the same (e.g. combination vaccine DPT combining diptheria, pertusisis and tetanus antigens). Combination vaccines can be useful to over-come logistic constraints of multiple injections, and accomodate for a children’s fear of needles and pain.
Vaccines may be monovalent or polyvalent. A monovalent vaccine contains a single strain of a single antigen (e.g. Measles vaccine), whereas a polyvalent vaccine contains two or more strains/serotypes of the same antigen (e.g. OPV).