Polio Prevention in India: Can India be polio-free by 2009?

India continues to be among the only remaining five reservoir of polio virus in the world, despite decades of intensive preventive programmes against the disease. Of the total 1,315 cases of poliomyelitis reported worldwide in the year 2007, over 60% of cases (874) occurred in India

Most recently two more new cases were reported both WPV3 cases from Moradabad, Uttar Pradesh (UP). However, the total number of polio cases for 2009 have come down to 21, so far, compared to 165 cases at this time last year.

What is Polio?

Poliomyelitis (polio) is a highly infectious disease caused by a virus. It affects the nervous system, and can cause total paralysis in a matter of hours. It can strike at any age, but affects mainly children under three (over 50% of all cases).

The virus enters the body through the mouth and multiplies in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. One in 200 infections leads to irreversible paralysis (usually in the legs).

Amongst those paralysed, 5%-10% die when their breathing muscles become immobilized. Although polio paralysis is the most visible sign of polio infection, fewer than 1% of polio infections ever result in paralysis.

Poliovirus can spread widely before cases of paralysis are seen.  After initial infection with poliovirus, the virus is shed intermittently in faeces (excrement) for several weeks. During that time, polio can spread rapidly through the community.

How is polio spread?

In the remaining polio endemic countries, poliovirus is mainly passed through person-to-person contact. Most people infected with the poliovirus do not develop polio paralysis or other symptoms of polio infection. However one in 200 people do have symptoms and can become paralyzed. The virus enters the environment through faeces of people infected then is passed to others especially in situations of poor hygiene. The poliovirus can also infect persons who have been vaccinated and can be carried by them. Such individuals will not develop polio, but can carry the virus in their intestines and can pass it to others in conditions of sub-standard hygiene. The disease may infect thousands of people, depending on the level of sanitation, before the first case of polio paralysis emerges. Individuals can carry the virus in their intestines just long enough to transmit to others.

WHO considers a single confirmed case of polio paralysis to be evidence of an epidemic – particularly in countries where very few cases occur.

How can polio be prevented?

There is no cure for polio, it can only be prevented through immunization. Polio vaccine, given multiple times, almost always protects a child for life.

Oral polio vaccine (OPV) is highly effective and inexpensive (about 5 per dose, or Rs 1.5 per child.) A study carried out in an isolated Eskimo village showed that antibodies produced from subclinical wild virus infection persisted for at least 40 years. Because the immune response to oral polio vaccine is very similar to natural polio infection, it is expected that oral polio vaccination provides similar lifelong immunity to the virus.

Polio paralysis

Once established in the intestines, poliovirus can enter the blood stream and invade the central nervous system – spreading along nerve fibres. As it multiplies, the virus destroys nerve cells (motor neurons) which activate muscles. These nerve cells cannot be regenerated and the affected muscles no longer function. The muscles of the legs are affected more often than the arm muscles. The limb becomes floppy and lifeless – a condition known as acute flaccid paralysis (AFP). More extensive paralysis, involving the trunk and muscles of the thorax and abdomen, can result in quadriplegia. In the most severe cases (bulbar polio), poliovirus attacks the motor neurons of the brain stem – reducing breathing capacity and causing difficulty in swallowing and speaking. Without respiratory support, bulbar polio can result in death.

WHO’s polio eradication goals

In May 1988, the World Health Assembly committed the member nations of the World Health Organization (WHO) to achieve the goal of eradication of poliomyelitis virus from the face of earth. The key targets of the goal were:

• no cases of clinical poliomyelitis associated with wild poliovirus
• no wild poliovirus found worldwide despite intensive efforts to do so.

 Following a concerted effort,  the Americas (last case in 1991, Peru; Region certified polio-free in 1994), the Western Pacific Region (last case in 1997, Cambodia; Region certified 2000), and the European Region (last case in 1998, Turkey; Region certified 2001), were certified polio-free by WHO.

In 1988, the Government of India  committed the nation to the goal of  global polio eradication. Since 1995, the Ministry of Health and Family Welfare, Government of India has been conducting immunization and surveillance activities aimed at the complete elimination of poliovirus and paralytic polio for the country.

Polio vaccination in India

In India, vaccination against polio was initiated in 1978 under Expanded Programme on Immunization (EPI) and the coverage achieved by 1984 was around 40% of all infants with 3 doses of Oral Polio Vaccine (OPV). In 1985 the Universal Immunization Programme (UIP) was launched and implemented in phased manner to cover all districts in the country by 1989-90. During 1986 the UIP was accorded the status of a Technology Mission under the banner of the Technology Mission on Immunization.

This resulted in significant increase in coverage to over 95% during 1990-91 and is being sustained over 90% since then. The number of  reported cases of polio declined from 28757 during 1987 to 3265 in 1995.

 At this stage, in pursuance to the World Health Assembly Resolution of 1988, in addition to administration of routine OPV through the Universal Immunization Program, the Pulse Polio Immunization (PPI) Programme was launched in 1995-96 to cover all children below the age of 3 years. In order to accelerate the pace of polio eradication, the target age group was increased from 1996-97 to all children under the age of 5 years. This resulted in further decline in number of polio cases to 1005 reported during 1996.

The primary strategies for achieving eradication of polio are:

• Attaining high routine immunization: immunize every child aged <1 year with at least 3 doses of oral poliovirus vaccine (OPV). Paralytic polio can be caused by any of 3 closely-related strains (serotypes) of poliovirus. Trivalent OPV (OPV3) provides immunity against all 3 types.
• Three routine OPV doses should be received by infants at ages 6, 10 and 14 weeks.
• National Immunization Days (NIDs): Conduct Pulse Polio Immunization (PPI) programme by providing additional OPV doses to every child aged <5 years at intervals of 4-6 weeks. The aim of NIDs/PPI is to “flood” the community with OPV within a very short period of time, thereby interrupting transmission of virus throughout the community.

The PPI programme was intensified by the addition of extra immunization rounds, adding a house-to-house “search and vaccinate” component in addition to providing vaccine at a fixed post.

The number of PPI rounds conducted during any particular year is determined by the extent of poliovirus transmission in the country. In recent years, several rounds have been conducted throughout the year – especially in the northern states of Uttar Pradesh and Bihar, which have carried a heavier burden of poliovirus – in an attempt to break the last chains of transmission.

· Surveillance of acute flaccid paralysis (AFP) to identify all reservoirs of wild poliovirus transmission. This includes AFP case investigation and laboratory investigation of stool specimens collected from AFP cases, which are tested for polioviruses in specialized laboratories.

· “Mopping-up” immunization: when poliovirus transmission has been reduced to well-defined and focal geographic areas, intensive house-to-house, child-to-child immunization campaigns are conducted over a period of days to break the final chains of virus transmission.

The objective of AFP surveillance was to detect the exact geographic locations where wild polioviruses are circulating in the human population. All cases of acute flaccid paralysis in children aged <15 years are rigorously investigated by a trained medical officer, with collection of stool specimens to determine if poliovirus is the cause of the paralysis. Analysis of the location of polioviruses isolated from AFP cases allows programme managers to plan immunization campaigns (Pulse Polio Immunization) to prevent continuing circulation of virus in these areas.

In the Global Polio Eradication Initiative (PEI), acute flaccid paralysis is defined as:

Any case of AFP in a child aged <15 years, or any case of paralytic illness in a person of any age when polio is suspected. Acute: rapid progression of paralysis from onset to maximum paralysis. Flaccid: loss of muscle tone, “floppy” – as opposed to spastic or rigid. Paralysis: weakness, loss of voluntary movement. Any case meeting this definition undergoes a thorough investigation to determine if the paralysis is caused by polio.

The wild poliovirus type 3 (WPV3) outbreak that commenced in UP in mid-2007 and spread to Bihar is declining rapidly since January 2008. This follows extensive use of monovalent oral polio vaccine type3 (mOPV3) in both states.

Central Bihar is the highest risk of persistence of transmission of WPV1. The central UP districts -Sitapur, Bahraich, Gonda, Balrampur, Siddhartnagar, Barabanki, Faizabad, and Sultanpur have in the recent past yielded long chain WPV1 isolates. WPV1 was active in this area in 2007, with the last reported case in UP being in Sultanpur in November 2007. There is a risk that WPV1 is still circulating in this area. The districts forming the eastern and southern edge of western UP – Shahjahanpur, Farrukhabad, Ferozabad, Etah, Mainpuri, and Kannauj -have also yielded long-chain WPV1, which was active in this area until August 2007 (the last case in Kannauj).

Despite not having reported WPV1 for more than one year, the historical centre of WPV1 in India (Moradabad and adjoining districts of Meerut, Muzaffarnagar and Bareilly sub-divisions) should still be considered as a risk for ongoing circulation.

The persistence of transmission in West Bengal for several months following introduction of WPV1 from Bihar in late 2007.

WPV1 was isolated from an environmental sample in Mumbai in March 2008. The city with very significant mobile populations (particularly moving from and to UP and Bihar), and Mumbai regularly detecting WPV from the endemic states. While WPV3 has spread to other states, it has not caused further multi-case outbreaks. With periodic use of mOPV3, incidence of WPV3 cases should remain at low levels for the remainder of 2008, setting the stage for interruption of its transmission in 2009.

India held a sub-national Immunization Day (SNID) was held in the first week of March. The next Supplementary Immunization Activity (SIA), on 5 April, will cover Uttar Pradesh, Bihar, and selected high-risk districts of India, targeting 30.5 million children with mOPV1.

The Government of India has agreed to switch the 24 May SNID from mOPV3 to mOPV1 vaccine, targeting 69.1 million children in Uttar Pradesh, Bihar and other selected areas. A further SIA in UP, Bihar and selected areas will be held at the end of June.

The orders placed by the Government for 75 million doses each of mOPV3 and mOPV1 will form an adequate emergency reserve (covering 4 to 5 large scale, 3 round mop-ups with each type).

NPSP hopes India would be able stop WPV1 transmission this year and could be the first among the remaining endemic countries to eliminate the most dangerous poliovirus.