There are 3 types of wild poliovirus, referred to as types 1, 2 and 3. Trivalent oral polio vaccine (tOPV) used in most countries is made using an attenuated strain of all 3 types of poliovirus. Monovalent oral polio vaccine-1 (mOPV1) is made using only the attenuated strain of type-1 poliovirus and immunizes only against that type (type 1). Except that it does not contain types 2 and 3, mOPV1 is in all other respects similar to tOPV.

In September of 2004, the Ad Hoc Advisory Committee for Polio Eradication – the global advisory body for the eradication effort – reviewed different possibilities for enhancing the impact of eradication activities that were taking place, particularly in the most important endemic countries. Because the AACPE believed that the data showing the potential impact of using mOPV1 was very strong, it recommended the use of mOPV1, in conjunction with other eradication activities, for certain areas where only wild poliovirus type-1 was circulating. Subsequently the national advisory groups on polio eradication in both Egypt and India, following their review of the data, recommended that mOPV1 be used.

mOPV1 offers important advantages in certain situations where wild poliovirus type 1 is still circulating because it increases the impact of each immunization contact with a child. Monovalent OPV1 provides an increased immunity to type 1 poliovirus compared to tOPV for the same number of doses. This is because with tOPV there is some interference between the three types of poliovirus when they are generating an immune response in the vaccinated child, and in the monovalent vaccine this does not occur. A very important advantage is that the monovalent vaccine produces a much stronger response than tOPV in children being immunized for the first time, including very young babies; since nearly all cases of polio now are children under two years of age, this is very significant. Additionally, if children immunized with mOPV1 are subsequently exposed to wild poliovirus type 1, they will excrete less virus and for a shorter period of time, limiting the possibility of further transmission.

No, mOPV1 will be used as an adjunct to existing immunization activities. tOPV will continue to be used for most campaigns in endemic areas and for routine childhood immunization.

No, monovalent oral polio vaccines for all the 3 types of polioviruses were used extensively in the early days of polio vaccination in the late 1950s and early 1960s, so there is a great deal of historical experience of these vaccines. Since no OPV manufacturer has recently produced monovalent vaccines, it is necessary to go through the process of licensing mOPV1 again.

Although wild poliovirus type 2 has not been found circulating anywhere in the world since 1999, type 3 continues to circulate extensively in west and central Africa, and in Pakistan/Afghanistan. mOPV1 only offers protection against poliovirus type 1, and is therefore only suitable for use in endemic areas where type 3 poliovirus is no longer circulating, or is at very low levels. The greatest effect of mOPV1 will also be felt where type 1 circulation has persisted in highly endemic reservoir areas. In Egypt and India, population density and birth rates are very high, and the transmission of wild poliovirus type 1 is at its most efficient. In Egypt no type 3 wild poliovirus has been detected since 2000 and wild poliovirus type 1 is responsible for all cases of polio. In India, in 2004 wild poliovirus type 1 caused more than 95% of polio cases. In the past 12 months, wild poliovirus type 3 has only been detected in 3 districts in western Uttar Pradesh; in Mumbai/Thane no type 3 has been detected for more than 2 years and in Bihar for more than 1 year. These are therefore ideal places to introduce mOPV1 as an additional tool for immunization during selected campaign rounds. It is important to note that in these countries and areas trivalent OPV will continue to be used for most immunization campaigns and that routine immunization of children with tOPV will also continue, to ensure that they are protected against all poliovirus types that could be exported from other polio-affected areas.

mOPV1 is as safe for a child as tOPV and will give faster protection against wild poliovirus type 1.

In the target areas mOPV1 campaigns will supplement the current campaign schedule. In areas where mOPV1 is used, vaccination campaigns will still have to reach every child during every round. However, because each contact with a child will deliver greater immunity, it is expected that wild poliovirus type 1 will be eradicated more quickly than with trivalent OPV. The earlier eradication of wild poliovirus will eventually lead to a reduction in the number of campaigns needed in these endemic areas.

After extensive discussions between WHO, UNICEF, and the prequalified manufacturers and fillers of OPV, two manufacturers have expressed their interest in making mOPV1 available. Sanofi Pasteur is working towards licensing mOPV1 and will produce 50 million doses of mOPV1 vaccine in the first half of 2005, and the intention is that this vaccine will be used in Egypt. Panacea is currently working with national regulatory authorities in India to license mOPV1 for use in India. When these vaccines become available, they will be procured through UNICEF, once the necessary procedures are completed. A US $10 million grant from the Bill & Melinda Gates Foundation is enabling the development of the vaccine.

In all respects of storage, handling, and use, mOPV1 is the same as tOPV. The vials and instructions are exactly the same, although labels will distinguish mOPV1 from tOPV. The vaccine will be administered through immunization campaigns to all children below the age of 5 years.

Manufacturing, licensing, and release of mOPV1 will be overseen by the French, Egyptian and Indian regulatory agencies: Agence Francaise pour la Sécurité Sanitaire des Aliments et des Produits de Santé; National Organization for Drug Control and Research of Egypt; and Central Drugs Standard Control Organization of India. - Out of 18 cases 8 are from Bihar, 7 from UP, one each from Uttaranchal, Delhi and Jharkhand - Most recent Wild Polio case ONSET 08th May 2005 - Location of most recent case(s) District Araria, Bihar, India

Latest update on polio eradication as of 17th June 2005:

• P1 WILD POLIO CASES = 18
• P3 WILD POLIO CASES = 0
• TOTAL WILD POLIO CASES = 18
• TOTAL DISTRICT INFECTED = 17

• Out of 18 cases 8 are from Bihar, 7 from UP, one each from Uttaranchal, Delhi and Jharkhand
  
• Most recent Wild Polio case ONSET 08th May 2005
  
• Location of most recent case(s) District Araria, Bihar, India
  
  

Last Updated on 1-8-2005

Questions And Answers On Monovalent Oral Polio Vaccine Type 1 (mOPV1)“Issued Jointly By WHO and UNICEF”.Pediatric Oncall [serial online] 2005 [cited 2005 August 1];2. Available from:
http://www.pediatriconcall.com/fordoctor/Medical_original_articles/oral_polio_vaccine.asp