VOL: 102, ISSUE: 39, PAGE NO: 44
Helen Bedford, PhD, RHV, is senior lecturer in children's health, Centre for Paediatric Epidemiology and Biostatistics, Institute of Child Health, London
Laura Lane, BA, RN (Child), is immunisation nurse specialist, Immunisation Department, Centre for Infections, Health Protection Agency, LondonPneumococcal disease is caused by the bacterium Streptococcus pneumoniae. Based on their different polysaccharide (...
Pneumococcal disease is caused by the bacterium Streptococcus pneumoniae. Based on their different polysaccharide (sugar) outer capsules, over 90 serotypes of the organism have been identified, although not all of these are responsible for serious infections. Commonly the organism is carried in the nose and throat (nasopharynx) with no apparent symptoms. Rates of carriage are high among very young children (Hussein et al, 2005) and exposure to cigarette smoke and attendance at day care are particular risk factors for carriage (Greenberg et al, 2006).
The organism is spread from person to person by coughing and sneezing. Whether an individual develops infection and the severity of the infection depends on factors such as age, state of the immune system and the virulence of the infecting serotype.
Pneumococcal disease manifests as invasive infections such as meningitis, septicaemia and bacteraemic pneumonia, and non-invasive infections which include non-bacteraemic pneumonia, otitis media (infection of the middle ear) and sinusitis.
Age and incidence rates
Rates of pneumococcal disease are highest in children under five years old - particularly those under two years, and in older people (65 years and older). Other at-risk groups include people who have had a splenectomy or have a non-functioning spleen and those with some chronic diseases.
About one in 6,000 children under the age of five will acquire invasive pneumococcal disease (IPD) in England and Wales. In 2004-2005 there were 731 confirmed cases of IPD in children under five, 94 of which were meningitis (Health Protection Agency, 2006).
The true number of cases of non-invasive pneumococcal disease is less clear since microbiological confirmation of the infection is difficult and is often not carried out.
However, Melegaro et al (2006) estimate that there are almost 5,000 hospital admissions for pneumococcal pneumonia and over 275,000 GP consultations for pneumococcal otitis media in children under five years of age each year.
Outcome of pneumococcal disease
Invasive pneumococcal disease has potentially serious consequences. Bacteraemia can lead to septicaemia, which carries a high mortality rate and Streptococcus pneumoniae is now the second most common cause of meningitis in children in England and Wales after meningococcal B infection (Davison and Ramsay, 2003). Pneumococcal meningitis has higher mortality and complication rates than Haemophilus influenzae type b (Hib) and meningococcal meningitis.
As many as 10-15% of affected children die as a result of pneumococcal meningitis and over 50% of survivors have long-term problems including sensori-neural hearing loss, learning impairment, cerebral palsy and seizures (Bedford et al, 2001).
The pneumococcus is the most common single cause of bacterial pneumonia and, in childhood, can lead to complications such as empyema (collection of purulent fluid in the pleura) and bacteraemia. Otitis media can result in glue ear and perforation of the ear drum. These may, in turn, lead to hearing loss affecting speech and language development.
In the past, pneumococcal infections were successfully treated with penicillin but more recently the bacteria have developed resistance to penicillin and other antimicrobial agents, such as erythromycin. Concerns about antibiotic resistance have increased the emphasis on prevention through vaccination.
Plain polysaccharide vaccine (Pneumovax II)
The vaccine is prepared from the polysaccharide capsule of the bacteria. It contains 23 of the 90 serotypes which account for 97% of the invasive pneumococcal disease in England and Wales (Melegaro et al, 2006). The vaccine was licensed in 1983 and is recommended for all adults over 65 years and individuals with medical conditions that increase their risk of infection (Department of Health, 2006).
But the limitations of the vaccine are:
- It only provides short-term protection;
- The boosting effect on the person's immunity with subsequent doses is limited;
- It is not very effective against non-invasive diseases;
- It does not reduce nasopharyngeal carriage;
- It is not immunogenic (provoking an immune response) in children under two years, who are a greatest risk of invasive disease. This is because the immune system of very young children responds poorly to the polysaccharide capsule and does not mount an adequate immune response to it.
In this vaccine the polysaccharide is linked or conjugated to a protein carrier. These are immunogenic in young children and unlike the plain polysaccharide vaccine, a good booster response is observed when a further dose is given after the primary course.
The seven-valent conjugate vaccine (Prevenar) contains seven pneumococcal serotypes, conjugated to a non-toxic variant of diphtheria toxin. These serotypes are responsible for 69-79% of the reported cases of IPD in children under five years in England and Wales (Melegaro et al, 2006).
Results from a trial of the conjugate vaccine in the US involving nearly 38,000 children showed it was highly effective in preventing invasive disease. There was a total of 40 cases of IPD caused by the serotypes contained in the vaccine, and all but one case occurred in the control group. In addition there was a significant reduction in otitis media (Black et al, 2000). A study in Finland involving 1,662 infants found that the conjugated vaccine resulted in 57% fewer episodes of otitis media caused by the seven serotypes covered by the vaccine (Eskola et al, 2001).
As with other conjugate vaccines, studies have found the vaccine is well-tolerated and it can be given at the same time as the other vaccines in the routine infant schedule.
In the US use of the conjugate vaccine in young children has resulted in significant herd immunity, with reduced disease in older age groups who have not been vaccinated. This is not only due to the direct effect of reducing the amount of disease but also indirectly, as a result of the reduction of nasopharyngeal carriage of the organism in those who have had the vaccine (Centers for Disease Control, 2005).
The new vaccine schedule
Infants are now offered doses of PCV at two and four months and a booster at 13 months. At the same time as the new vaccine was introduced other changes to the routine infant immunisation schedule were made. These involve Hib and meningococcal C (Men C) vaccines. The number of primary doses of Men C were reduced from three to two, given at three and four months, and a booster of Men C/Hib will be offered at 12 months as a combination vaccine.
In addition, there will be a catch-up campaign and all children under the age of two years will be offered pneumococcal vaccine. The number of doses they require depends on their age.
Why are these changes necessary?
When Hib vaccine was introduced in 1992, it was also offered to all children up to the age of four in a catch-up campaign. Uptake was high and there was a dramatic decline in notifications of invasive disease. This situation persisted until the late 1990s when numbers of cases of Hib disease began to increase. There are a number of reasons for this but part of the explanation is that immunising all children up to the age of four years when the vaccine was introduced rapidly led to herd immunity, providing protection for young infants even when their own antibody levels declined (Finn and Heath, 2005). It initially masked the fact that the immunity from immunisation in infancy is relatively short-lived. Other countries that offer the Hib vaccine give boosters in the second year of life and it is now clear that this is important to ensure long-term protection.
Studies of Men C vaccine have also found that although there is high short-term efficacy among infants who are given three doses (Balmer et al, 2002), long-term protection of those immunised early in infancy is poor (Trotter et al, 2004), and that the greatest part of the serological response occurs after the first two primary doses (Southern et al, 2006). Therefore the number of primary doses has been reduced to two, with a booster included at 12 months to provide longer-term protection. A booster dose of the new pneumococcal vaccine will be given at the same time as the MMR vaccine at 13 months.
One of the major concerns about use of the pneumococcal conjugate vaccine is that although disease caused by the serotypes in the vaccine has been markedly reduced, other serotypes may take their place and cause disease. While there is evidence that this has happened to a small extent in the US, it does not outweigh the huge reduction in disease cause by the vaccine serotypes (CDC, 2005). This will be monitored closely in the UK.
Issues for health professionals
The new schedule requires that, at four months, three injections are given at a single visit. There has been concern that this may not be acceptable to parents. Similar concerns were voiced when Hib vaccine was introduced as this required an additional injection, but in practice, uptake was high. Parents will feel more confident about accepting this third injection if the health professional administering it is also confident and explains its importance (Woodlin et al, 1995).
In infants, it is recommended that vaccines are administered by IM injection in the anterolateral aspect of the thigh, which means multiple injections may need to be given in the same limb. When this is the case, they should be at least 2.5cm apart with the needle perpendicular to the skin to prevent the vaccines mixing.
The addition of a booster of Hib/Men C means another visit is required at 12 months. This is an excellent opportunity to remind parents about MMR vaccine, scheduled at 13 months, and to discuss any issues and answer any questions. Many parents will welcome this and health professionals should make the most of this additional immunisation visit.
Many parents find the process of having their children immunised distressing. Health professionals can minimise this distress by giving them information, answering their questions, taking their concerns seriously and allaying their fears. There will inevitably be many questions about the new schedule and the reasons for it, and practice nurses and health visitors will be at the forefront of giving this advice (Bedford and Lansley, 2006).
It is likely that parents will have little awareness of pneumococcal disease. This was the case when Hib vaccine was introduced but information provided by health professionals overcame this potential barrier. Although the pneumococcus is an important cause of meningitis, its name suggests pneumonia, which is more commonly considered to be a disease of older people rather than of infants and children. Some of the questions parents will ask include details about pneumococcal disease, the safety and efficacy of the seven-valent pneumococcal conjugate vaccine and the reasons for the addition of boosters of the conjugate vaccines to the immunisation programme.
The new immunisation schedule gives children additional protection against another serious infection and extends protection against some of those we already immunise against. This development is to be welcomed and will result in a significant improvement in the health of the UK's children.