Pneumococcal vaccination is effective in real life against invasive pneumococcal infections (pneumonia, meningitis, sepsis ...) but requires an adaptation of the vaccination protocol in France.
Public Health England conducted national surveillance for invasive pneumococcal infections (pneumonia, meningitis, etc.) in England and Wales to estimate the efficacy of 23-valent non-conjugated pneumococcal vaccine in the elderly.
The incidence of invasive pneumococcal disease in 2016/17 was compared to the 2000-2003 rates, when neither 23-valent non-conjugated pneumococcal vaccine nor conjugate pneumococcal vaccines were used in these areas.
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 non-conjugated 23-valent pneumococcal vaccine to cover the new types of pneumococci that appear. On the other hand, the efficacy of 23-valent non-conjugated pneumococcal vaccine is moderate and would only be effective for up to 4 years. These results, published in The Lancet Public Health, lead to reflect on the French vaccination schedule that does not correspond exactly to these data in real life.
Moderate efficacy of the unconjugated vaccine
The overall efficacy of 23-valent non-conjugated pneumococcal vaccine is 27% (95% CI, 17-35) after adjustment for age, associated diseases, and year of infection. The effectiveness of the vaccine decreases with time since vaccination, from 41% for those vaccinated within two years (95% CI, 23-54) to 34% for those vaccinated 2 to 4 years ago (IC 95%, 16-48) and 23% for vaccinees aged 5 years or older (95% CI, 12-32 years).
The frequency of occurrence of invasive pneumococcal infections for serotypes not included in 23-valent conjugate vaccines did not decrease after routine use of 23-valent non-conjugated pneumococcal vaccine, but has increased significantly since then. the introduction of the conjugate vaccine in 2006.
Understanding the pneumococcus
Pneumococcus (Streptococcus pneumoniae) is a bacterium that has a capsule, composed of complex sugars (polysaccharides) enveloping the bacterium and partly explaining its virulence.
Depending on the nature of these polysaccharides, 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
The vaccines used against pneumococci are made from the sugars that make up the capsule. There are unconjugated vaccines and conjugate 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 remove the portage of pneumococcus in the throat (causing the transmission of person to person) and the protection conferred is short-lived.
In conjugate vaccines, the conjugation of pneumococcal polysaccharide antigens to a protein improves the efficiency 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 valencies: 1, 3, 5, 6A, 7F and 19A. This 13-valent conjugate vaccine provides protection against pneumococcal infections and carriage of this bacterium, and it can be used as early as two months of age.
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 significantly in children under two years old.
However, an increase in the frequency of infections due to some serotypes not covered in the heptavalent conjugate vaccine (including serotypes 1, 7F and 19A) was increasing until the arrival of the 13-valent conjugate vaccine, which contains these serotypes. .
The real-life English study shows that the same phenomenon will be reproduced with the 13-valent conjugate vaccine, which requires combining it with the 23-valent non-conjugated pneumococcal vaccine.
The vaccination protocol in France in the elderly or frailized recommends a dose of 13-valent conjugate vaccine then a dose of non-conjugated vaccine 23-valent 8 weeks later, then again a dose of vaccine 23-valent at least 5 years later the last dose. The results of this study support a shortening of the recall time for 23-valent non-conjugated pneumococcal vaccine.