Fifty-five years after the first successful vaccine trial in the US, the battle to eradicate the disease is almost complete, writes KEVIN CONNOLLY
ON APRIL 12th, 1956, results of the first successful polio vaccine trial were presented in the US. It is difficult for those under 60 years of age to appreciate the global impact that this announcement had.
Historically, polio has been the world’s greatest cause of disability. In the 1950s, outbreaks were occurring worldwide. Cork was in the grip of a polio epidemic; nearly 550 patients, mostly children, were admitted to hospital in a four-month period with paralysis caused by poliovirus. The outbreak caused near hysteria. As Cork teams were in both men’s All-Ireland finals, Dubliners were afraid of infected people travelling to Croke Park. “Let Cork . . . keep their polio and not infect our clean city.”
Shortly after the trial, huge vaccine campaigns started. In two years, polio cases fell by almost 90 per cent in the US. The vaccine was introduced into Ireland in 1957. Within six years, only sporadic cases were occurring, and by 1985 polio had been eliminated from Ireland.
In 1988, the World Health Organisation, Unicef and others began a campaign to stop transmission of polio throughout the world. The programme has cost nearly $9 billion (€6.3 billion), and requires $750 million (€525 million) each year.
Polio cases have fallen by more than 99 per cent, from 350,000 cases in 125 countries in 1988 to only 946 reported cases in four countries in 2010 (Afghanistan, India, Nigeria and Pakistan).
In 2010, more than two billion children were immunised, preventing five million cases of paralysis and 250,000 child deaths. However, as long as one person remains infected, all countries are at risk. In 2009 to 2010, 23 previously polio-free countries were re-infected due to imports of the virus. These included the Russian Federation, Tajikistan and Turkmenistan.
What is polio?
Polio is an ancient disease. A carved style from Egypt (1570-1342 BC) shows a man with a paralysed, withered leg. It occurred only sporadically until the first epidemic in late 19th-century Sweden. Over the next 50 years, epidemics occurred in other industrialised countries.
It is spread mainly in faeces, aided by poor sanitation. More than 90 per cent of those infected have no symptoms. About 4 per cent have mild fever, sore throat, diarrhoea and lethargy. A smaller number develop viral meningitis with headache, sensitivity to light and neck stiffness. Those usually fully recover.
Unfortunately, 0.1-2 per cent develop paralytic polio, when the virus affects nerves supplying the arm, leg and respiratory muscles, causing limb paralysis and breathing difficulty.
The paralysis is more likely to occur, and to be more severe, in adulthood. One in 1,000 children and one in 75 adults develop paralysis. In the under fives, paralysis of one leg is commonest; in adults, paralysis of the chest, abdomen and all limbs is more likely. Half of those paralysed recover fully, one- quarter have mild disability and the remainder are left with severe disability.
Some who survive and recover develop muscle weakness, extreme fatigue or paralysis decades later. This is termed post-polio syndrome. Overall, 5-10 per cent of patients with paralytic polio die.
The endgame
Major barriers to elimination remain. In India, poor sanitation facilitates spread of the virus; malnutrition and diarrhoea reduce the immune response of the vaccine. Devastating floods in Pakistan last year and the conflict in Afghanistan have posed major problems for vaccine administration.
But major efforts are ongoing. In India, over five days in February, 2.5 million workers visited 68 million homes to inoculate 172 million children. They also visited schools and nomadic enclaves so no child would be missed.
In October 2010, a mass immunisation campaign in 15 African countries reached 72 million children, and in Afghanistan 7.8 million children were targeted. If the will and the funding continue, polio will shortly follow smallpox into the dustbin of history.
Dr Kevin Connolly is a member of the National Immunisation Advisory Committee
