Indian Pediatrics 1998; 35:723-725 

Efficacy of Two Dose Measles Vaccination in a Community Setting

Inspite of extensive immunization coverage under the universal immunization programme (UIP) in Maharashtra, measles still remains a major cause of childhood morbidity and mortality. In developing countries like India, more than 2 million children die of measles every year. Live attenuated measles vaccination is an effective means of reducing the incidence of measles in many countries(1). India has introduced measles vaccination in the VIP since 1985. Presently the age of immunization with measles vaccine is nine months. With a potent vaccine, the seroconversion rates have been reported to

vary from 81.8 to 100% in various series(2-4). Our own experience with measles vaccine is similar with excellent seroconversion using measles or MMR(5-7). However, some cases of measles are being consistently reported in various areas of our country. This observation was perplexing. Two doses of measles vaccination have been suggested as a strategy to control measles. The present study was therefore designed to compare the occurrence of cases of measles in a community setting wherein children would receive either ,a single dose or two doses at an interval of six months.

Subjects and Methods

The present study was undertaken in joint collaboration with Pune Municipal Corporation and Sassoon General Hospitals-Department of Pediatrics for a period of 2 years from 1994 to 1996. Two ICDS blocks, equally matched for hygiene, sanitation, and approximate population were selected for the study. In both of these blocks, the type of housing was kuccha slum hutments. These blocks were named Block A and Block B. Both the blocks were visited in October 1994 by two teams of doctors, nurses and other paramedical health workers. A total number of 8990 children below 12 years of age from Block A were selected and 8550 children from Block B were enrolled. These children were the recipients of all national programmes identically. Out of these, Block A had 1560 children between the age of 9 months and 1 year and Block B had 1380 children aged between 9 months and 1 year. The extent of coverage was 95%.

In October 1994, all these children were given live attenuated measles vaccine manufactured by Serum Institute of India. The vaccination was done on a fixed day in the week, following usual precautions in both the Blocks. In the month of April 1995, same children from Block A were given a second dose of measles, as MMR vaccine. After a gap of 7 months a survey was

undertaken by a separate team of doctors and health workers from Pune Municipal Corporation from January 1996 to April 1996 to study the number of clinically detectable cases of measles in both of these blocks. Diagnosis of measles was made clinically on the basis of high fever, measly face, maculopapular rash occuring at the height of fever, classical distribution of rash and brawny desquamation after the acute phase. Koplicks spots were looked for; if the child was examined during the first few days of illness.

Results

Only 3 children (0.19%)in Block A suffered from measles whereas 16 children (1.16%) in Block B had a clinical attack of measles (p < 0.01) (Table I). The rash was studied on presence/absence basis. No complications of measles were reported. On detailed history taking, all episodes reported were to be the first attack of measles. The overall incidence rate is not as yet available from the Government statistics.

Discussion

Several authors have reported the immunogenecity and reactogenecity of measles vaccine in India. The seroconversian rates have ranged from 81.8 to 100% in various series including our own(2-6).

There have however been no studies at the community level with some longitudinal followup to clinically determine the efficacy. In the present study, it was observed that children in Group A who received two dose measles vaccine, there were only 3 cases of clinical measles Dceuring in the block in the ensuring year while in Group B, 16 children developed measles (p < 0.01) The ages of the children who developed measles were below 5 years. Since both the blocks had received ICDS coverage in earlier years, it was presumed that earlier vaccine coverages were identical. Records of the past 2 years also showed a target coverage of 90 and 91.8% in Blocks A and B, respectively. Cold chain maintenance was upto date.

 

This study, thus throws light on two important points. Do infants in our country need two doses or do we need to have 100% vaccine coverage by single dose to increase the efficacy? Presuming that the vaccine is 95% protective and the number of immunized children is also 95%, every year we will have 10% of the susceptible population which is likely to get measles. It is also known that when the susceptible population increases beyond 30%, an outbreak can occur. It may be logical to conclude that by giving two doses of measles vaccination we reduced the number of susceptible infants. Therefore, the occurrence of disease in Block A was much less than in Block B. Several countries have two dose measles vaccination schedule in their immunization programs. Various studies have shown a significant decrease in prevalence of measles after the two dose measles vaccimition(8,9).

It is therefore concluded that in a community setting, two dose measles immunization may prove superior to one dose in controlling the occurrence of a large number of cases. However, replications of findings in larger studies in a community. setting in the country is required.