8 February, 2010
By Ted Purlain
New Delhi, India
The vaccine, launched in Bihar state in January, offers protection from the P1 and P3 types of polio strains.
About 42 million children were expected to receive the new drops over the weekend. Overall, 170 million children are likely to be immunized during the current round of immunization.
There are three strains of wild poliovirus – P1, P2 and P3. Type 2 wild poliovirus was eliminated in 1999. Efforts are still on to eradicate the P1 and P3 strains.
As P1 is the more virulent type of the two, the current strategy is to eliminate it first while keeping P3 under control.
Initially, a trivalent Oral Polio Vaccine (which caters to all three strains of the wild polio virus) was used in the campaign. Subsequently, a more efficient monovalent vaccine was introduced to handle the P1 and P3 strains.
While the monovalent vaccine has been found to be effective in containing the transmission of P1, it has affected the control of transmission of P3.
As many as 33 states and union territories are free of indigenous transmission of the wild poliovirus. Uttar Pradesh and Bihar remain the two endemic states where indigenous transmission continues.