Pneumococcal disease is caused by the bacterium Streptococcus pneumoniae which commonly causes infection of the respiratory tract i.e. lungs, sinuses or ears. In vulnerable people S. pneumoniae can invade the blood stream and cause septicaemia and meningitis. This may tragically lead to deafness or mental disability if the patient does not succumb to their illness. People at the extremes of age, i.e. old and young, are particularly susceptible to the complications of pneumococcal disease because of their underdeveloped or aging immune systems which cannot adequately fight off the bacteria.
Pneumococcal disease is spread from person to person through close contact with respiratory tract secretions e.g. saliva and sputum. The bacteria may live in the respiratory tracts of people without causing harm. This is called “colonisation”. Scientists still do not fully understand the chain of events that causes the bacteria to transform from being colonisers to invaders that make the person sick by causing pneumococcal disease.
Treatment of pneumococcal infections with penicillin and other similar antibiotics used to be very effective. Unfortunately, an increasing number of pneumococcal strains have become resistant to these drugs, making treatment very difficult and limiting therapeutic options. In this age of antibiotic resistant bugs, prevention of disease, through vaccination, is becoming more essential.
It is estimated that immunisation prevents approximately 2.5 million premature deaths a year. It is also the most cost-effective public health intervention in the history of medicine, even more than the development of antibiotics.
Types of vaccines:
There are two different types of pneumococcal vaccines available:
- PPSV23: Pneumococcal polysaccharide vaccine is made from the polysaccharide (sugar-like) capsule of 23 different strains of S. pneumoniae. This capsule is the main target of the body’s immune response during pneumococcal infection. The body produces antibodies when exposed to this polysaccharide capsule (also called the “antigen”), whether by infection or immunisation and therefore the next time the immune system is exposed to the same antigen the immune cells are prepared and can rapidly produce killing antibodies because the body still has a “memory” of the antigen via specially produced immune memory B-cells. Children under 2 years of age have an immature immune system that cannot produce memory cells to the polysaccharide capsule, therefore PPSV23 vaccines is not effective in this age group.
- PCV13: Pneumococcal conjugate vaccine is similar to PPSV23, but the capsular polysaccharide is joined to a protein that will induce memory cells even in children <2years of age. It is very difficult and expensive to conjugate (join) a protein to a sugar. The initial vaccine covered only 7 strains (called PCV7), but now 13 strains are included in this vaccine.
Who should be vaccinated?
Vaccination with PCV13 is recommended for all children younger than 5years of age. Pneumococcal vaccination is part of the South African vaccination programme called the Expanded Programme on Immunisation (EPI). According to the EPI schedule the PCV13 vaccine is given to children at 6weeks of age, then again at 14 weeks and the last dose of the series when they are 9 months old. Recently a booster dose was brought into the schedule which is given at 12-15 months of age.
It is recommended that adults 65 years of age or older receive both the PCV13 and the PPSV23 vaccines. The vaccines cannot be given at the same time, so the recommendation is to give the PCV13 vaccine first and then a PPSV23 vaccine about 6months to a year later. Because PSV13 has only recently been licenced for use in adults, there are those people who received only the PPSV23 vaccine as it was the only vaccine available for adults before 2011. In those cases, the patient can receive the PSV13 a year after receiving PPSV23.
PCV13 with a PPSV23 booster 1 year later is also recommended for adults 19 years or older with conditions that weaken the immune system, such as HIV infection, organ transplantation, leukaemia, lymphoma, and severe kidney disease.
As discussed earlier, Streptococcus pneumoniae causes severe invasive infections in susceptible people. Antibiotic resistance is a reality and resistance to commonly used antibiotics is becoming a serious threat to medical treatment of infections. Pneumococcal vaccination does not prevent colonization with S. pneumoniae, but prevents the bacteria from causing invasive infections. It not only prevents infection in vaccinated people, but provides a “herd immunity” by helping to prevent transmission of the bug to close contacts of the sick patient who could contract the bacteria from secretions e.g. through coughing or sneezing. Thus, vaccination has exponential benefits to the community by preventing transmission to people who are potentially vulnerable to infection. This has been demonstrated by studies that have shown a dramatic decrease in the number of pneumococcal infections since the introduction of pneumococcal vaccination into the childhood vaccination programme.
References: 1. a short history of vaccination. In: Plotkin SA, Mortimer EA, eds. Vaccines, Second Edition. Philadelphia: WB Saunders, 1994: 1 2. http://www.immunize.org/vis/ppsv.pdf 3. http://www.cdc.gov/vaccines?vpd-vac/ pneumo/default.htm 4. http://www.cdc.gov/vaccines/acip/ 5. Kobayashi et al; Intervals between PCV 13 and PPSV 23 vaccines: recommendations of the Advisory Committee on Immunisation Practices (ACIP); MMWR 2015; 64 (34): 944-7 6. http://www.afro.who.int/en/south-africa/ country-programmes/4245-expanded-program-on-immunisation-epi.html 7. South Afr J Epidemiol Infect 2008; vol 123(1)
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