More than 1000 people were infected, around 70 died, schools and other facilities were closed and there stern warnings against swimming in harbours.

The polio epidemic that gripped New Zealand for more than two years after World War II was considered the most persistent outbreak of the feared disease that the country had experienced up to that time.

But for numbers of cases and deaths, the epidemic of 1947-49 wasn't the worst. The most deaths in one year were in 1925, when 173 people died.

This Thursday marks 70 years since children were allowed back to school in central Auckland after an enforced closure through the summer and autumn.

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Caused by a virus, polio is an incurable disease whose symptoms can range from none at all (95 per cent of cases) through to paralysis (up to 2 per cent) in limbs or the respiratory system.

The virus is spread in faeces and in saliva. It can also be passed on through contaminated water, milk and food.

New Zealand's first major polio outbreak was recorded in 1914. It killed 25 people. Epidemics, typically lasting a year or two, occurred every few years until the early 1960s, after the introduction, in 1956, of vaccines which eventually eradicated the disease.

In 1947, the first case of what would become a major outbreak was detected in Auckland in mid-November. There was a rapid increase in cases in the city and then in Waikato and Taranaki.

The epidemic spread throughout the North Island during the summer and peaked in Wellington at the start of winter 1948. By the end of the year it had dispersed widely in the South Island. Monthly tallies slowly tailed off during 1949 but dropped to low levels only until early 1952, when a new epidemic got going.

Jean Ross, in a 1993 history thesis at the University of Canterbury, wrote that within days of the first cases in Auckland, schools in the North Island were closed, followed on December 8 by those in the South Island.

"On 11 December, children were prohibited from staying in motor camps and attending Sunday schools, and two days later inter-island travel by school children was forbidden.

"The usual quarantine applied: all home contacts under 16 were quarantined for 14 days from date of removal of the patient to hospital, and home contacts over 16 were quarantined for the same time if their work brought them into contact with children, or if they were food handlers."

In Auckland, hospital patients in polio wards were not allowed any visitors, not even their parents.

The Herald reported in February 1948 that the district's medical officer of health, Dr L. S. Davis, warned against swimming at Auckland's harbour beaches, as well as the city beaches from St Heliers to Milford on the North Shore.

"The waters of the Waitemata and Manukau Harbours are undoubtedly polluted and bathing in these areas unquestionably is still unwise," Davis said.

The Herald continued: "Dr Davis' opinion was supported by another doctor, who said the poliomyelitis virus would continue to occur in general sewage for many weeks, and it was known the virus could survive in polluted waters for many days."

Ross said swimming pools in Auckland were closed to children, and in Wellington to everyone; In Auckland adults were allowed to use chlorinated pools.

In Hamilton a Christmas parade was permitted, provided the children stood at least 6 feet (1.83m) apart.

The Ministers of Health, Mabel Howard, and Education, Terry McCombs, announced in late-February 1948 that schools would reopen on March 1. But just days after the announcement, when faced with continuing new cases and protests by worried parents writing to the Herald, the Government backtracked, re-imposing the ban at central and some south Auckland schools and then later some in Waikato and Rotorua too.

In a speech to the Crippled Children Society, Howard said she must be satisfied there was no danger of renewing the epidemic by reopening schools. The safety of allowing children back to class was being assessed, although the outbreak appeared to be lingering in Auckland.

"After all, what does a few weeks of education that a child can catch up later mean when we may have children crippled for life?"

Children were expected to complete lessons by correspondence and listen to school broadcasts on radio.

In April, the Government said all schools closed by the epidemic, except at seven places in Waikato, the Bay of Plenty and Taranaki, would reopen on April 19. Despite that, Herald archives indicate individual schools continued to close for periods in the following months when children were diagnosed with polio.

Once the epidemic had waned, by September 1949, the paper reported that for the "first summer since 1947", swimmers could swim at the city's harbour beaches "with the approval of the Health Department".

Auckland medical officer of health Dr A. W. S. Thompson said the risk of catching polio from the harbour water was negligible.

Other diseases, however, might still be contracted, such as typhoid, but he did not know of any cases in the city traced to harbour water. It was definitely inadvisable to eat shellfish from Auckland beaches.

Health Department clerks managing parental consent cards for the 36,000 children to be vaccinated against polio in 1957. Photo / Herald archives
Health Department clerks managing parental consent cards for the 36,000 children to be vaccinated against polio in 1957. Photo / Herald archives

The Ministry of Health says the last case of "wild" polio virus in New Zealand was in 1977. No cases of vaccine-associated paralytic poliomyelitis have occurred in New Zealand since the introduction of inactivated polio vaccine in 2002.

The World Health Organisation says polio continues to be transmitted between people in three countries: Afghanistan, Nigeria and Pakistan.

New Zealand's worst polio years

• 1916 - 1018 new cases; 123 deaths

• 1925 - 1159; 173

• 1937 - 816; 39

• 1948 - 963; 52

• 1952 - 890; 57

• 1955 - 703; 29

• 1956 - 897; 50