Calcutta, July 18: Just as India was making progress in checking polio, Bengal threatens to spoil the effort because of what state officials themselves admit to be “complacency”.

Four cases of the dangerous P1 form of the infection have been detected in the state this year out of six in the country — a nosedive after the state recorded zero polio cases last year.

State family welfare officer J.M. Chaki admitted that “complacency” following last year’s good showing may have led to some children being “left out” of the vaccination drive.

“Second, the quality of sanitation and water supply is quite poor in places like Samsherganj in Murshidabad, which are magnifying the danger,” Chaki said.

Three of the P1 polio cases were found in Murshidabad — two in Samsherganj block and one in Khargram block —and the fourth in Murarai II block of Birbhum.

“It’s extremely worrying; all eyes are on Bengal now,” an expert involved with polio eradication said from Delhi.

The overall incidence of polio (P1 and P3) has fallen in the country with 24 cases detected this year till last week, five of them in Bengal, compared with the 124 cases in the same period last year. (See chart)

But the large number of P1 cases in Bengal poses a significant risk to India’s polio programme. The virus may now be reintroduced from Bengal into Bihar and Uttar Pradesh, which together accounted for 24 of the 28 P1 cases in 2009 but none this year, National Polio Surveillance Project sources said in Delhi.

Bengal officials shifted the blame on migrants from other states.

“There is no doubt that the polio situation in the state has become quite serious. But we must keep in mind that although there has been no P1 cases this year so far in Uttar Pradesh and Bihar, still the viruses brought in by the migrant population last year from these places are in circulation and are triggering the polio spread,” Chaki said.

Senior state officials involved in polio vaccination said poor support from local political leaders in mobilising communities for the vaccination drive too contributed to the problem.

The National Polio Surveillance Project sources agreed that the Bengal P1 virus’s genetic links suggested it was probably imported from Bihar through mobile populations in late 2009.

They said Bengal needed a series of immunisation rounds to cover all target children, with special focus on those in the high-risk blocks of Murshidabad and adjoining Birbhum and Malda. Another high-risk group is the migratory population, which makes Calcutta and its neighbourhood vulnerable.

Chaki said two P1-specific pulse polio rounds had been carried out in Bengal in the past two months to arrest the trend.

Of the three strains of the polio virus — P1, P2 and P3 —P2 has become extinct internationally and P1 is the more dangerous of the surviving strains. Since last year, the Centre and international agencies have invested a lot of effort and money into eliminating the P1 infection.

An expert from Delhi said that several rounds of pulse polio vaccination had been carried out in the country last year, including dedicated P1 vaccine rounds.