No 21 - 2012

PCV coverage & invasive pneumococcal disease 2011

The 7-valent conjugate pneumococcal vaccine (PCV7) has formed part of the Danish Childhood Vaccination Programme since 1 October 2007.

As from week 16, 2010, the 13-valent conjugated pneumococcal vaccine (PCV13) was delivered instead of PCV7, EPI-NEWS 15/10. However, vaccinating physicians were encouraged to exhaust their stock of PCV7 before introducing PCV13. 2011 was thus the first year in which only PCV13 vaccines were given.

The vaccine protects against invasive pneumococcal disease (IPD) caused by 13 pneumococcal serotypes (PS). An IPD case is defined on the basis of positive culture or PCR of Streptococcus pneumoniae in cerebrospinal fluid, blood or other normally sterile material.

Background

PCV is given at the ages of 3, 5 and 12 months in the Childhood Vaccination Programme. Children who were aged 4-11 or 12-17 months on 1 October 2007 were offered three or two vaccine doses, respectively, as part of a catch-up programme, EPI-NEWS 37a+b/07, which had an estimated coverage for initial PCV of 76% and 58%, respectively, EPI-NEWS 19/11. Prior to the introduction of PCV, the 13 PS included in the currently used vaccine caused 91% of all cases of IPD in children below the age of five.

Vaccination coverage

Vaccination coverage was recorded using the administrative service codes indicated by GPs when settling first, second and third vaccinations, respectively. Coverage was calculated on the basis of data drawn from the Childhood Vaccination Database on 16 April 2012. There is a 2-3-month delay from a vaccination is administered until it is registered in the Childhood Vaccination Database. The coverage of the Childhood Vaccination Programme for birth cohorts 2007-2010 ranged from 84% to 92% for the initial PCV, 81-92% for the second PCV and 79-90% for the third PCV, Table 1. For the 2011 birth cohort, vaccination had not been concluded at the calculation date.

Changes in IPD incidence

Figure 1 shows the age-specific incidence of laboratory-confirmed IPD cases per 100,000 inhabitants before and after the introduction of PVC to the Childhood Vaccination Programme in 2007.
The report is based on national Danish data from the Neisseria and Streptococcal Reference Laboratory, Statens Serum Institut.
The overall incidence in the population of IPD prior to PCV, defined as the mean annual incidence during the eight-year period from 2000 to 2007, was 20 cases/100,000 (an average of 1,055 annual cases). The incidence decreased to 16 cases/100,000 (908 annual cases) in 2011.

The decrease in IPD incidence was strongest in children < 2 years: from 54 cases per 100,000 prior to PCV to 12 cases per 100,000 in 2011. The latter figure halves the 2010 incidence of 23/100,000.

For IPD caused by the PS comprised by the PCV13, the incidence in the age group < 2 years decreased from 49/100,000 prior to PCV to 3/100,000 in 2011. This is equivalent to an estimated 94% programme efficiency against the 13 PS among children < 2 years, counting vaccinated as well as unvaccinated children.

The mean number of notified cases of pneumococcal meningitis in children below five years of age decreased from 23 prior to PCV to five in 2011. In the same period, the 30-day mortality following IPD in children under five years of age decreased from 2% to 0% in 2011.

Commentary

In 2011, the shift from PCV7 to PCV13 has brought an additional decrease in the IPD incidence in children < 2 years.  After the introduction of PCV to the Childhood Vaccination Programme, a small increase was observed in the IPD incidence of the PS not comprised by the PCV7. The increase concerned in particular types 7F, 1 and 19A which are, however, all included in the currently used PCV13.

Generally, a 20% decrease has been observed in IPD incidence, corresponding to approximately 137 prevented IPD cases in 2011. This is owed to a direct effect among those vaccinated as well as an indirect effect in the entire population, primarily among the elderly > 65 years.

PCV coverage is approximately one to two percentage points lower than that of the DTaPIPV/Hib vaccine which is given concurrently. The lower coverage means that in the 2010 birth cohort, which consists of approx. 64,000 children, 500-1,300 children, depending on the dose number, will receive the DTaP-IPV/Hib, but not the PCV vaccination. There reason why this vaccine was deselected is unknown, but the vaccine's efficiency is assessed to be satisfactory at the current coverage.

(P. Valentiner-Branth, C.C. Bjerre, P.H. Andersen, Dept. of Infectious Disease  Epidemiology, L. Lambertsen, H. Ingels, S. Hoffmann, H.B. Konradsen, DBMP)
                                        
23 May 2012