Anti-pneumococcal vaccination is effective in real life against invasive pneumococcal infections (pneumonia, meningitis, sepsis, etc.) but requires an adaptation of the vaccination protocol in France.
Public Health England conducted national surveillance of invasive pneumococcal disease (pneumonia, meningitis, etc.) in England and Wales to assess the effectiveness of the 23-valent unconjugated pneumococcal vaccine in the elderly.
The frequency of invasive pneumococcal disease in 2016/17 was compared to rates in 2000-2003, when neither the 23-valent unconjugated pneumococcal vaccine nor the pneumococcal conjugate vaccines were used in these regions.
It appears that the pneumococci responsible for invasive infections change with the introduction of conjugate vaccines, which makes it necessary to combine them with the 23-valent non-conjugate pneumococcal vaccine to cover the new types of pneumococci that appear. On the other hand, the efficacy of the 23-valent non-conjugated pneumococcal vaccine is moderate and would only be effective for a maximum of 4 years. These results, published in The Lancet Public Health, lead to reflection on the French vaccination schedule, which does not correspond exactly to these data in real life.
Moderate efficacy of the unconjugated vaccine
The overall efficacy of the 23-valent unconjugated pneumococcal vaccine is 27% (95% CI, 17–35) after adjusting for age, associated diseases and year of infection. Vaccine effectiveness declines with time since vaccination, from 41% for those vaccinated within two years (95% CI, 23–54) to 34% for those vaccinated 2–4 years previously (95% CI, 95%, 16–48) and 23% for vaccinees aged 5 or more years previously (95% CI, 12–32 years).
The frequency of occurrence of invasive pneumococcal disease for serotypes not included in 23-valent conjugate vaccines did not decrease after routine use of 23-valent unconjugated pneumococcal vaccine, but has increased significantly since. the introduction of the conjugate vaccine in 2006.
Understanding pneumococcus
The pneumococcus (Streptococcus pneumoniae) is a bacterium which has a capsule, composed of complex sugars (polysaccharides) enveloping the bacterium and partly explaining its virulence.
Depending on the nature of these polyosides, there is a great diversity of pneumococci, called serotypes: there are about a hundred of which only a few are currently responsible for invasive pneumococcal infections.
Understanding pneumococcal vaccines
Vaccines used against pneumococci are made from the sugars that make up the capsule. There are unconjugated vaccines and conjugated vaccines.
The unconjugated vaccine contains 23 pneumococcal serotypes (1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 20 , 22F, 23F and 33F). Its main advantage is the broad serotype coverage, but it is not effective before the age of two years, it is not able to suppress pneumococcal carriage in the throat (the origin of person-to-person transmission). person) and the protection conferred is short-lived.
In conjugate vaccines, conjugation of pneumococcal polysaccharide antigens to protein improves the efficacy of pneumococcal immunization. The first conjugate vaccine contained 7 serotypes (4, 6B, 9V, 14, 18C, 19F and 23F). Since 2010, in France, the conjugate vaccine contains six complementary valences: 1, 3, 5, 6A, 7F and 19A. This 13-valent conjugate vaccine provides protection against pneumococcal infections and the carriage of this bacterium, moreover, it can be used from the age of two months.
In practice
In France, since the use of the heptavalent pneumococcal vaccine (containing serotypes 4, 6B, 9V, 14, 18C, 19F and 23F), the frequency of infections due to vaccine serotypes, which are also the most resistant to antibiotics, decreased sharply in children under two years of age.
However, an increase in the frequency of infections due to certain serotypes not covered in the seven-valent conjugate vaccine (notably serotypes 1, 7F and 19A) was increasing until the arrival of the 13-valent conjugate vaccine, which contains these serotypes .
The English real-life study demonstrates that the same phenomenon will recur with the 13-valent conjugate vaccine, which requires combining it with the 23-valent non-conjugate pneumococcal vaccine.
The vaccination protocol in France for the elderly or vulnerable recommends a dose of 13-valent conjugate vaccine then a dose of 23-valent non-conjugate vaccine 8 weeks later, then again a dose of 23-valent vaccine at least 5 years later the last dose. The results of this study are in favor of a shortening of the booster period of the 23-valent non-conjugated pneumococcal vaccine.
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