Fears of a revival

Published : May 19, 2006 00:00 IST

To reduce transmission children should receive 7-9 doses of OPV in the first 9-12 months. - V. SREENIVASA MURTHY

To reduce transmission children should receive 7-9 doses of OPV in the first 9-12 months. - V. SREENIVASA MURTHY

Uttar Pradesh and Bihar frustrate India's efforts at polio eradication after a missed WHO deadline.

LAST year the country recorded the least number of cases of the wild polio virus (WPV): 66 cases in 35 districts nationwide, the majority of which are in two pockets in Western Uttar Pradesh and Bihar. The number was 134 the previous year in 43 districts. Though the country failed to meet the revised global deadline of polio eradication by 2005, it was heading there despite the fact that it was one of the last countries to achieve it. The virus was essentially of Type 1, with only four isolated cases of Type 3. The last of Type 2 was seen way back in October 1999. And even within Type 1, the distinct genetic lineages had reduced from 12 clusters to just 2, clear evidence of low and localised transmission. So eradication by 2006 seemed a distinct possibility.

"The very low transmission detected in the peak transmission season of 2005, despite significant improvement in surveillance sensitivity, indicates that WPV is now having a great deal of difficulty in surviving in India," the India Expert Advisory Group (IEAG) on polio eradication said in December 2005. "The period of maximum pressure on the virus, the very low transmission season, is nearly upon us. The key action in the coming months will be to conduct excellent sub-national immunisation days in January and February in Uttar Pradesh and Bihar, particularly in the high-risk districts, to ensure that the virus is stopped in the low transmission season," it said. "The IEAG remains confident that transmission can be stopped during the coming low season, that the overall strategies being followed are correct and appropriate, and they are proving their effectiveness," the group, constituted under the World Health Organisation (WHO) and Indian government National Polio Surveillance Project (NPSP), noted.

But four months into 2006, hopes have receded. So far there have been 24 cases reported as against 14 - one of Type 3 and the rest of Type 1 - by mid-May last year. "April is normally the lowest transmission month. Virus transmission has occurred even during low transmission months. The virus has survived," pointed out Sobhan Sarkar, former Deputy Director, Child Health, Union Ministry of Health and Family Welfare and now a consultant to the polio programme. The peak polio season is between August and October. Clearly, the signs are ominous and a definite cause for concern.

More pertinently, of the 15 cases up to May 2005, the endemic pockets of Uttar Pradesh and Bihar reported only five and four cases respectively. The rest were isolated cases - one each in Delhi, Gujarat, Haryana and Punjab and two in Jharkhand - but all migrants from Bihar. Also despite the detection of wild virus strains (originating from Uttar Pradesh and Bihar) in the sewers of Maharastra's Mumbai and Thane, no evidence of transmission was found.

This year, however, all the cases are from 14 districts north of River Ganga in Uttar Pradesh and Bihar. Mumbai's sewers have not revealed any signs of the virus yet. So it is reasonable to expect a higher number of cases by the year-end in these States than last year's 29 and 30 cases respectively.

The absence of cases in the non-endemic areas speaks for the success of the immunisation programme in these States, but in Uttar Pradesh and Bihar its failure is glaring. Despite intensive immunisation campaigns through national immunisation days and sub-national immunisation days, including intensive door-to-door visits in these regions, the strategy has not been able to the break the transmission chain in these districts of the two States. "The possibility of an outbreak in high transmission months cannot therefore be ruled out," Sobhan Sarkar said.

Why this apparent increase in virus transmission? "The answer is simple," said Jacob John, the eminent virologist and Emeritus Professor at the Christian Medical College (CMC), Vellore. "The force of vaccination is lower or slower than the force of transmission. Where the force of transmission is very high (illustrated by paralysis in the very young - the median age is below 18 months), in such places immunisation must have near 100 per cent vaccine efficacy."

The strategy being followed under the WHO's Global Polio Eradication Initiative (GPEI), which in 1988 set the deadline as 2000 and later moved it to 2005, is the use of the live (but attenuated) oral polio vaccine (OPV), as opposed to the inactivated (killed) injectible polio vaccine (IPV). The latter is known to have better efficacy. However, for cost reasons and greater ease of use the WHO recommended the OPV. To compensate for the lower efficacy, it recommended a higher dose regimen and this naturally impinged on the efficiency of the surveillance and vaccine delivery programme. The other major advantage claimed is the herd immunity effect of OPV, that is, it confers immunity to even unvaccinated children through contact and exposure to the live vaccine virus shed in their environment. This is still a matter of contention among medical scientists (see Frontline, January 2, 2004).

On the wide geographic variation in virus transmission and eradication with a few worldwide foci holding out, Jacob John wrote in the Journal of Indian Medical Research in September 2004:

"The worst end of the spectrum may be characterised by an extremely high force of virus transmission and an extremely low efficacy of OPV ... With OPV, achieving near 100 per cent efficacy means that 7-9 doses in the first 9-12 months of age are necessary to predictably interrupt transmission in such communities. Three doses give 70 per cent, five doses 90 per cent and 7-9 doses 97-99 per cent. Any hitches - programmatic or community acceptance - that affect the speed of vaccination with sufficient number of doses in greater than 90 per cent of infants will slow down success. I suspect both [factors] are operating in the two States."

This is indeed what the data bear out even as the country spends over Rs.1,000 crores a year on polio eradication. Of the 24 cases, 17 did not receive any routine immunisation dose at all. Of them, all but one (in Bihar) received vaccination as part of supplementary immunisation activities. Community acceptance amongst Muslims - 16 of the 24 cases are of Muslims, large numbers of whom live in the affected areas - seem to be a major obstacle in full immunisation coverage, particularly in Moradabad district, which reported seven cases, according to Sobhan Sarkar. Members of the community fear that the polio vaccine will cause impotency.

The various strategies adopted to overcome this community barrier led to improvements but they are still insufficient to reach the goal of virus eradication. In Uttar Pradesh and Bihar, besides immunisation at the booth door-to-door campaigns have been carried out for five to seven days after that. The campaigns have often been carried out twice a day, in the morning and in the evening, to maximise coverage.

In the door-to-door campaigns, usually two persons made up the field team. In Uttar Pradesh and Bihar, a Muslim was included in the team to allay the fears of Muslim families. Initiatives such as leaving the vaccine with someone in the community have also been tried out, said Sobhan Sarkar. As a result of these efforts, unlike the earlier direct rejection of the vaccine (see Frontline, January 2, 2004), evasion has now become more subtle and covert. The families concernced said that the child was not at home or had gone out of town. "As a result, 10-12 per cent of the children are effectively missing in the immunisation coverage," said Shoban Sarkar.

Another important factor was management failure in the delivery operations, involving the supervision and monitoring of teams and Chief Medical Officers (CMOs), the Block Medical Officers (BMOs) and the District Magistrates attached to the programme. "Monitoring of data has, however, improved and the incidence of false reporting has declined," said Sobhan Sarkar.

For the past three years, the other States did not have any indigenous wild virus cases. Whenever they had an isolated case, it was traced to importation from Uttar Pradesh or Bihar, he said. "The wild virus is circulating only in 50-60 districts of these two States. The rest of the 550 districts are waiting for mop-up operations. Western Uttar Pradesh and Bihar are preventing the country from becoming polio-free," said Sobhan Sarkar.

The IEAG noted in its December 2005 report that the greatest risk to polio eradication in India was the ongoing transmission in Bihar. It said that WPV from Bihar had been exported not only to other States in India but to Nepal and Bangladesh as well. "Rapid action," the IEAG noted, "must be taken by the Union government and the State government to ensure that SIAs (Supplementary Immunisation Activities) in early 2006 are of excellent quality and that WPV transmission is interrupted in that State." Data up to April-end show that the number of cases in Bihar (7) are significantly fewer than in Uttar Pradesh (17). "The problem in Bihar is that most doctors are busy in private practice and are reluctant to devote time to the assigned duty," said Sobhan Sarkar.

One of the strategies to contain transmission was the introduction of the monovalent oral polio vaccine Type 1 (mOPV1) in the high-risk districts of Uttar Pradesh and Bihar as well as in Mumbai-Thane. The trivalent OPV vaccine (tOPV), in use since the beginning of the programme, is designed to elicit an immune response against all three virus types, whereas the monovalent vaccine confers immunity only against the Type 1 virus and is found to be more efficient, particularly in children and infants being immunised for the first time.

In general, three doses of tOPV is equal to one dose of mOPV1. This is because, with tOPV, there is competition among the three virus types to elicit immune response; the virus-attenuated vaccine particles attach themselves to the gut and tend to bring down the overall efficacy against a single virus type. It has been found that tOPV is most efficacious against Type 2, a little less against Type 3 and least against Type 1. Following the universal transmission of Type 1 virus among children less than two years of age in the country, this was considered the correct strategy. Type 1 is known to be the most transmissible among the three types. There are also isolated cases of Type 3 but these are more easily controlled by tOPV or monovalent OPV3.

Vaccination with mOPV1 was introduced during the national immunisation days in April-May 2005 and the sub-national immunisation days in June and August 2005. The routine immunisation programme, however, continued to use the trivalent OPV only. Compared with the incidence levels during the high transmission season in 2004, 13 districts of Uttar Pradesh showed a marked decrease in virus activity following the use of mOPV1. Jacob John recommended dropping the Type 2 vaccine altogether in favour of the Type 1 and Type 3 monovalent vaccines to be given in sequence even in routine immunisation, as has been done in some countries.

The increase in the number of cases in 2006 should not, however, be understood as owing to introduction of mOPV1. On the higher efficacy of monovalent vaccines, there is absolutely no doubt. As Jacob John pointed out, the vaccine had to be delivered and consumption by infants ensured. So concerted efforts would be needed in the high-risk regions not only in the use of monovalent vaccines but also in increasing the number of doses.

The remaining hope for eradication is that in 2006 the genetic lineages of transmission are only of two kinds in the two clusters of districts. Also, significantly, a lot of similarities exist in the geographical spread of the two genotypes in Uttar Pradesh and Bihar. So the transmission is localised and can be controlled just by implementing the WHO-recommended strategy of using OPV alone, notwithstanding its shortcomings, in a thorough and efficient manner to ensure 100 per cent coverage.

What other fresh strategies could be introduced to arrest the widespread transmission of WPV at this point of time? If seven to nine doses could be given to infants in these high-risk areas, they should, said Jacob John. Since infants are the most efficient amplifiers of viruses, transmission of WPV can be stopped. If that was not possible, he said, there may be shortcuts, such as giving the community all the routine vaccines on time and without shortages, particularly the measles and Japanese encephalitis vaccines. Then more doses of OPV may become easily acceptable. Yet another shortcut, he said, was to give the DPT-IPV combination instead of DPT alone and continue with OPV, as was being done now, and try to achieve as high a coverage as possible. Indeed, the national Technical Advisory Group on Immunisation has recommended a combination vaccine.

The IEAG is likely to make new recommendations at its meeting on May 3-4, which will determine the new strategies of the programme. Will the country eradicate polio by 2007 so that it is certified polio-free by 2010? Or will the finishing line keep disappearing into the horizon every time we approach it, as some sincerely believe, given the WHO strategies being adopted?

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