Eurosurveillance

ECDC

Protective Effect of Rubella Vaccination

 Rediger
 1 Published: 17.11.04 Updated: 17.11.2004 14:13:38
O. Ivanauskiene, D. Plytaitiene, N. Kriauciuniene, E. Liakiene
Department for Communicable Diseases Control, Kaunas Public Health Centre, Lithuania
Rubella incidence has increased in 1999-2000 in Kaunas district as well as throughout Lithuania, predominantly among children under eleven years of age. Rubella was diagnosed only clinically, laboratory confirmation was not used. Experimental immunization of a group of 220 children showed the vaccine effectiveness of 77%

Introduction

In 1993, vaccination against rubella was introduced in Lithuania with one dose at 15-16.5 months of age and one at 12 years of age. About 95% of the targeted population is vaccinated every year.

The incidence of rubella in Kaunas district of Lithuania dropped markedly in 1994-1995 and was then stable for several years. However, in 2000 a new increase was noted (Fig 1).

The incidence doubled from 19 per 100 000 in 1999 to 36 per 100 000 in 2000. More than 98% of cases were among children under 11 years of age. No cases of congenital rubella syndrome were reported. All cases of rubella were diagnosed clinically; no serological diagnostic test was used. A similar increase has been observed throughout Lithuania. Cases have been sporadic and the seasonal distribution has not changed, with most cases occurring during the spring.

We report here a case control study among children in Kaunas district of Lithuania to measure the protective effect of rubella vaccination against clinically diagnosed rubella.

Methods

The study was performed in the largest children’s outpatients clinic in Kaunas (Silainiai, Kalniečiai, Dainava, Sančiai and Centras). The largest number of rubella cases had been reported from the area serviced by these clinics. The clinics register all information regarding children’s diseases and vaccinations in outpatient’s cards.
We selected at random outpatient’s cards of 100 children (cases) who had been diagnosed with rubella in 2000. The control group included 222 children without rubella. The case group represented approximately half of the children from these districts who had rubella in 2000.

EpiInfo version 6.04b was used to analyse the vaccine effectiveness (95% confidence interval).

Results

Twenty-eight of the children had not been vaccinated against rubella. Among the 72 who were vaccinated, 37 (51%) had a delayed vaccination. Two of the controls had not been vaccinated. Among the 220 who were vaccinated, 79 (36%) had a delayed vaccination. The vaccine effectiveness of 97.7% (95% confidence interval 89.9% - 99.5%).
The 72 vaccinated children who later contracted rubella had been vaccinated between 1 month and 9 years earlier with the majority of vaccinations given 3-6 years earlier (Table 1).

Table 1. Period from primary rubella vaccination to onset of clinically diagnosed rubella during 2000 in 72 vaccinated children

Period

Number of children

1 month

1

6 months

3

9 months

1

1 year

2

2 years

4

3 years

10

4 years

15

5 years

15

6 years

13

7 years

4

8 years

3

9 years

1

Discussion

Rubella incidence has increased in Lithuania during the past few years, but to a much lower maximum level than before vaccination was introduced. The vaccine offers a very high protection against clinical rubella. Children not vaccinated are at risk of contracting rubella.

There are two main limitations to our study. Firstly, rubella was diagnosed on clinical grounds only. Many other diseases with rash may resemble rubella. This is a weakness in our study and the results should be interpreted with caution. Secondly, we did not adjust our case control data for age.

During the period 1993-1997 the supply of rubella vaccine was irregular and transport conditions were suboptimal. This may explain why many children who were vaccinated in during this period were apparently not protected. The vaccinated children contracted rubella 4 to 6 years after the primary vaccination. To improve this situation we suggest that medical institutions ensure proper conditions during vaccine transport and storage and that rubella vaccination is not delayed. We also suggest that serological studies should be performed on school children to see whether children vaccinated during 1993-1997 lack immunity against rubella. If so, these children may have to be revaccinated earlier than at the scheduled 11 years of age.

Currently, children in Kaunas district are still at risk of contracting rubella, although the vaccine offers very good protection.


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