The Tamil Nadu government’s recent measles-rubella vaccination drive is finally picking up with 1.05 crore children having received the vaccination. The government’s plan was to vaccinate 1.76 crore children between the ages of 9 months and 15 years in a five-week immunisation drive. However, health officials faced stiff resistance in the first few weeks.

Much of the initial resistance was due to the acute discomfort of parents at the prospect of a government determined to vaccinate their children, even without parental consent. Health officials have not made the effort to tell parents why their children need or how they will benefit from this round of immunisation. Moreover, there were rumours circulated on whatsapp about side effects of the vaccine.

Most public health campaigns in Tamil Nadu have met with reasonable success in the past with the state reporting vaccine coverage rates of more than 95%. But, as data from the latest National Family Health Survey shows, coverage of the measles vaccine has fallen from close to 93% in 2005-’06 to 85% in 2015-’16.

The measles-rubella vaccination drive has currently been extended for a week till March 15 to make up for slow progress in the early days and there is a chance that the government will meet its targets.

Evolving immunisation programme

India’s Expanded Programme of Immunisation established in 1978 was renamed the Universal Immunisation Programme in 1985 and certain vaccines, like the measles vaccines were added. Periodic surveys like the National Family Health Surveys and the District Level Household Survey provide the government with assessments of the immunisation status of children. According to the National Family Health Survey in 2005-’06, the routine measles vaccination coverage at the national level was only 59%. This has risen to 81% in 2015-’16.

Mass immunisation drives are carried out with the aim of plugging immunisation gaps. The goal of the current measles-rubella vaccination drive is to immunise 41 crore children across India against the two diseases by 2020. Tamil Nadu is one of five states conducting the first phase of vaccinations.

“This decision was taken by two authorities – India’s National Technical Advisory Group on Immunisation and the South East Asian Regional Office of the World Health Organisation,” said Dr K Kolandaswamy, director at the Tamil Nadu department of public health and preventive medicine. “We supported the drive because we felt that would provide protection to any child who had missed being vaccinated [for measles] earlier in the state while strengthening the immunity of those who had.”

The pan-India drive will be held in three phases. Tamil Nadu is one of five states participating in the first phase. The government’s worry about children having missed immunisations earlier stems from a lack of maintenance of vaccination records. But parents who are certain that they have had their children vaccinated with the measles-mumps-rubella vaccine question the need for an additional dose.

Building herd immunity

The government is determined to ensure that no child is left behind through its mass immunisation drive to ensure and phenomenon called herd immunity.

“If a hundred people lived in a certain isolated area and only 90 of them received a vaccination against a particular disease, you’ll find that even the ten people who did not receive the vaccine would have a high degree of protection against that disease too,” said Dr Ramanan Laxminarayan, epidemiologist and director of the Center For Disease, Dynamics and Economic Policy, an independent health research organisation in New Delhi.

Herd immunity works because transmission of the disease-causing organism is broken when it cannot get past immunised children to the children who have not had their shots. Vaccinating in large numbers creates this herd immunity.

India’s large population that lives in dense communities is particularly vulnerable to epidemic outbreaks. Making sure that the population develops herd immunity protects the immunised, the non-immunised and others. “This could include people who are immunocompromised (such as the HIV positive), pregnant women, the very young or the elderly and those with chronic illness,” said Laxminarayan.

In order to build herd immunity effectively, a significant portion of the population must be immunised within a particular window of time. How much of a population needs to be vaccinated for immunity to set in varies based on the disease.

“To attempt to eliminate a disease like measles, at least 85% of our children must be [given the vaccine] at the same time,” said Dr Guna Singh, professor of paediatrics at the SRM Medical College Hospital in Chennai and a former president of the Indian Academy of Pediatrics.

“Herd immunity prevents the virus strain from remaining in circulation within the population,” said Dr AK Prasad, professor of virology and the president of the Indian Academy of Virologists. “By providing repeated doses, we not only make it possible to eliminate previously life threatening diseases, we also consistently strengthen the immune system.”

When people refuse the vaccination – as they have done during this vaccination drive – there may be too many gaps for a protective circle of herd immunity to be formed, rendering this sort of public health program ineffective.

“The way each child builds immunity after being vaccinated varies greatly and is dependent on many factors such as their age, overall health at the time and unique genetic make-up,” said Singh. “If children are malnourished or even anaemic at the time of vaccination, they may not develop full immunity against a particular disease at that time. This is why ‘catch-up doses’ such as the current MR drive are highly recommended, even if your child has already been vaccinated earlier.”

Strengthening waning immunity

India’s public programme to immunise against measles began in 1985 with a single dose vaccine given to a child at nine months. The Universal Immunisation Programme currently administers two doses of the measles vaccine, the first at 9 months and the second between 16 and 24 months. The Indian Academy of Paediatrics recommends that the measles-mumps-rubella vaccine be administered in two doses as well. Many parents have been following this schedule, especially when they get their children immunised by paediatricians in private hospitals. The current measles-rubella vaccine offered on this drive does not include vaccination against mumps, a disease which is not widely prevalent now and which would make the vaccine more expensive and unsuitable for a mass vaccination.

But studies show that even the two-dose vaccination may not result in children in a population having adequate antibody levels.

“These additional shots are essential to strengthen the waning immunity of the section of population that has already been vaccinated, while also protecting those who may not have received recommended coverage,” says Kolandaswamy. “We have a strong surveillance during immunisation in schools. In every school receiving the vaccine, the medical team administering it is alert to any allergic or adverse reactions.”