Vaccines against bacterial diseases

Summary

• Most vaccines against bacterial infections are effective at preventing disease
• Reactions can occur after vaccinations
• Vaccines are available against tuberculosis, diphtheria, tetanus, pertussis, Haemophilus influenzae type B, cholera, typhoid, and Streptococcus pneumoniae.

Tuberculosis (TB)

The vaccine for TB is the BCG vaccine (Bacille Calmette Guerain – named after the people who developed it). This vaccine is prepared from an organism closely related to Mycobacterium tuberculosis (the organism that causes TB). The vaccine organism has been cultured and recultured in a laboratory numerous times to make it weaker (attenuated). Unfortunately, the BCG vaccine does not confer great immunity against TB, but it does prevent some of the more dangerous forms (such as TB of the brain), especially in children. This vaccination is part of the standard vaccine schedule in South Africa. It is recommended for all children, except those who are infected with HIV.

The following three vaccines are part of the national immunisation schedule, and should therefore be administered to all children. They are usually combined into one injection - DTP (diphtheria, tetanus and pertussis).

Diphtheria

The vaccine for diphtheria contains an inactivated form of the diphtheria toxin. This toxin is responsible for many of the clinical features of diphtheria. If you’ve been vaccinated, you could still be infected by the organism (Corynebacterium diphtheriae), but the toxin would be neutralised by your antibodies, and the typical features of diphtheria would not appear.

Side-effects – the most important being anaphylaxis (severe allergic reaction) – are rare. Anyone who has had an allergic reaction to the diphtheria toxoid should not receive the vaccine again.

Tetanus

This is another infection where the disease is actually caused by a toxin produced by the organism rather than by the organism itself. Thus the tetanus vaccine is also an inactivated form of the toxin. Although everyone should have been vaccinated in childhood, you are at risk of tetanus at any age and should therefore get regular boosters (every 10 years is the current recommendation), or at least get a booster if you may have been exposed to the bacterium that causes tetanus (Clostridium tetani). Situations where you may be exposed include dog bites, injuries with soil contamination, wounds from rusty nails etc.

As with diphtheria, the most important side-effect of the vaccine is anaphylaxis, and the vaccine should not be given to anyone who has had an allergic/anaphylactic reaction to the toxoid previously.

Pertussis (whooping cough)

The vaccine for this condition consists of whole Bordetella pertussis organisms that have been killed. As mentioned earlier, this vaccine has been controversial because of some of the side-effects, including shock, uncontrollable crying and sometimes brain damage. These more serious side-effects occur very rarely, and it has actually been difficult to prove that the vaccine is responsible. Because of these side-effects, however, a great deal of research has been aimed at developing a new pertussis vaccine that contains only a portion of the organism combined with inactivated pertussis toxin. This acellular vaccine preparation has been shown to be almost as effective as the traditional vaccine, and has fewer side-effects.

The vaccine should not be given to anyone who has had an allergic reaction to it previously. It should probably also not be given to any child who had neurological symptoms after a previous dose, although this should be discussed very carefully with your doctor. Some people recommend that children with underlying neurological disorders should not receive the vaccine. This is debatable, and the decision should be made in consultation with your doctor. If there is an outbreak of pertussis in the community, it may be preferable to vaccinate the child anyway. In all situations, it is advisable to discuss vaccination options with our doctor before making a decision about whether or not to vaccinate your child or yourself.

Haemophilus influenzae type B

Although this organism can cause numerous infections – such as pneumonia, meningitis, ear infections, epiglottitis (severe inflammation and swelling of the epiglottis in the throat) – H. influenzae type B is commonly associated with severe infections in children (meningitis, epiglottitis, pneumonia).

Recently, a vaccine for H. influenzae type B was included in the routine immunisation schedule for children in South Africa. The vaccine contains a portion of the organism cell wall. Unfortunately, this portion of the cell wall is not very good at stimulating immunity on its own. It has therefore been attached to a protein carrier, which increases the immunogenicity (the degree of immune response) significantly. This vaccine has been shown to significantly reduce both death and disability due to invasive Haemophilus infections (especially Haemophilus meningitis).

Cholera

This infection, caused by V. cholerae, is responsible for severe watery diarrhoea, and often occurs in epidemics. Unfortunately, no completely effective vaccine for this condition exists, although a number of vaccines are in the development stage. The currently available cholera vaccine is an inactivated vaccine containing whole V. cholerae organisms, and its effectiveness is estimated at 50%. Although most authorities recognise that this vaccine is not fully effective, some countries still require documentation of vaccination before you can travel there.

Some of the newer vaccines consist of genetically modified organisms that cannot cause disease. These vaccines consist of live organisms that can be given orally and will stimulate immunity in the gut. These vaccines are not yet routinely available, but may become so in the future.

Typhoid

This is a potentially fatal infection caused by the organism Salmonella typhi. It is acquired by ingesting (swallowing) the organism in contaminated food or water. The older vaccines consist of killed organisms given by injection. Although this vaccine was effective, there were often side-effects. Therefore, a live attenuated strain of S. typhi was developed as a vaccine. This vaccine is given orally and is also effective, but without the side-effects. However, the safety of this vaccine in pregnant women and patients with weakened immune systems has not been established. A third vaccine (subunit vaccine) containing a portion of the organism’s cell wall is also available, and is given by injection.

Typhoid vaccines are not part of the routine immunisation schedule, but should be considered by people travelling to areas where clean food and/or water may not be available i.e. parts of South America, central Africa and possibly south-east Asia.

Streptococcus pneumoniae

This organism is a common (probably the commonest) cause of pneumonia as well as a common cause of meningitis in adults. Unfortunately, over 80 different serotypes (strains with slightly different surface antigens) exist. It would be very difficult to design a vaccine capable of inducing immunity to all of these serotypes, so vaccines have been developed against the serotypes most commonly responsible for infection.

There is a 23-valent vaccine (i.e. it provides immunity against 23 of the serotypes), consisting of cell wall components (a subunit vaccine). More recently, both 7- and 9-valent vaccines have been introduced. The advantage of these vaccines is that they are conjugate vaccines (i.e. the cell wall subunit of S. pneumoniae is linked to a protein carrier) and thus stimulate more effective immunity.

Vaccination against S. pneumoniae is recommended for people who don’t have a spleen (since they are more susceptible to infection with this organism), for the elderly (people over 65), for those with certain chronic heart and lung diseases, and for those with HIV infection. However, there is some debate about the value of this vaccine for HIV-infected individuals, since some studies have shown that it does not reduce the risk of death or illness in HIV-infected people.

Written by Dr Andrew Whitelaw, MBBCh (Witwatersarnd), MSc (UCT), FCPath (Micro) (SA) Senior registrar, Department of Microbiology, University of Cape Town and Groote Schuur Hospital.

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