THREE years after 2012-13, Sindh, particularly Karachi, is experiencing another measles outbreak. Physicians in Karachi and interior Sindh are informally reporting many measles cases. Though the case fatality rate is not yet known, typically in settings of high malnutrition, 5pc to 10pc of the affected children die. These outbreaks occur every two to three years in Sindh.

The measles vaccine is included in the free routine immunisation programme for children in Pakistan; they are supposed to receive at least two doses of the measles vaccine. The first dose is given at nine months and the second during the second year of life. Unfortunately, the coverage of the vaccine is low, especially in Sindh and Balochistan, and over time the pool of susceptible population increases, and when this pool reaches the critical threshold, a measles outbreak ensues.

Let’s take the hypothetical district X in Sindh with a population of 100,000 and an annual birth cohort of 3,000. According to the last Pakistan Demographic and Health Survey, immunisation coverage in Sindh was 29pc, against a target of over 85pc. We know that one dose when administered at nine months is 85pc effective in producing immunity. Hence, in our example, if 29pc of the 3,000 infants born that year received the vaccine that is 85pc effective, 740 infants would be protected and 2,260 unprotected.

The government’s response has been slow this time.

These numbers will double the following year. A measles outbreak typically occurs when the pool of unprotected children is more or less equal to the annual birth cohort of that community. Hence we’d expect a measles outbreak every two to three years in district X.

So if we are witnessing a measles outbreak, we must follow WHO guidelines related to its control. The steps involved include: real-time surveillance and reporting of cases; strengthening case management including provision of two doses of vitamin A to all cases; focused supplementary immunisation activities (SIAs) in affected areas; strengthening routine immunisation in affected areas; and an appropriate communication strategy for the public.

Given that there is no strong system for raising the alarm against outbreaks in Sindh, the government’s response this time has been relatively slow. A few mop-up vaccination campaigns are now planned in affected union councils of Karachi, but more urgency is required. Equally important is a long-term field-based surveillance system, so future outbreaks of infectious and other diseases can be promptly flagged.

Our focus on polio eradication is often taken as an excuse for not investing resources in other vaccine-preventable diseases. The polio eradication programme should in fact be leveraged to tackle other vaccine-preventable illnesses in a better way, eg combined national SIAs against measles and polio at least once a year.

The predictably recurrent measles outbreaks point towards another systems-level problem in our measles-control strategy. Like all WHO member countries, Pakistan’s immunisation programme has two doses of measles vaccine to be given to all children.

While the first dose in most developing countries is given at nine months, there are two choices on how to administer the second dose. In countries with well-functioning immunisation programmes where coverage of the first dose of measles vaccine is more than 85pc, it is recommended that the second dose be administered as part of the routine schedule, eg 15 months, to all children. In countries where immunisation coverage is not up to standard (Sindh has a coverage rate of 29pc, Balochistan 16pc), it is recommended that the second dose be given via regular (eg yearly) mass immunisation campaigns or SIAs.

During these mass campaigns, all children of a pre-specified age, usually between six months and five years, are given a dose of measles vaccine irrespective of their previous vaccination history. This approach is better for areas of low-performing immunisation programmes since SIAs are usually focused and cover a much larger proportion of children than those covered by the routine programme.

Despite having the last reported coverage of only 29pc in Sindh and 16pc in Balochistan, these provinces continue to follow the routine schedule for the second dose of measles. The last large-scale nation-wide measles SIA in Sindh was conducted in 2014 but the coverage was questionable.

It is true that regular mass immunisation campaigns are expensive because they require a high level of operational commitment and resources, but we have no other choice until our routine coverage of vaccines exceeds 85pc. Our choice until the time till coverage rates are improved is either to conduct regular, high-quality mass immunisation campaigns against measles or accept that our children will continue to die of measles every couple of years during inevitable outbreaks.

The writer is associate professor of pediatric infectious diseases, Aga Khan University.

asad.ali@aku.edu

Published in Dawn, April 15th, 2016