PhD Thesis - ResearchSpace@Auckland - The University of Auckland

Nevertheless, there were other contributory factors; the idea of vaccine failure was
mooted as a significant problem. This took two forms, firstly, the changing age at
which measles immunisation was deemed to be most advantageous and secondly, the
effectiveness of the measles vaccine. When measles vaccine was first introduced in
1969-70 babies were immunised at ten months old. This was changed to 12 months in
1974 and was reviewed again by the EAC in 1982 and changed to 15 months. This
gradual shift upwards was due to the recognition that there was less chance of primary
vaccine failure if immunisation occurred later. 81 However, this left a large number of
susceptibles, immunised at ten months, in whom measles could and did occur. Of the
12 children over eight years old hospitalised during the epidemic, nine were
immunised at ten months. 82 The Health Department commented that ‘it is to be
expected that measles will continue to circulate amongst such children’. 83
Furthermore a 1992 study indicated that in New Zealand measles vaccine had a failure
rate of 31 per cent with a one-dose regime by age ten. 84 Therefore, the Health
Department was unable to eliminate measles epidemics even if they had achieved 95
percent coverage required because the vaccine had over a 30 percent failure rate.
Measles would still occur in previously immunised children and epidemics would still
happen as there was a large pool of ‘susceptibles’. Subsequently, it was determined
that a two-dose regime would be required to maintain adequate levels. In November
1990 the Health Department replaced the single measles vaccine at 15 months with
MMR vaccine and the second dose was added in 1992 for Form 1. 85
Another concern was loss of potency of the measles vaccine through incorrect storage.
Throughout the 1970s and early 1980s the inadequacy of some doctors’ storage
facilities caused the Department to air their disquiet on several occasions. In 1979 a
number of cases of measles from around the country in immunised children were
drawn to the attention of the Department, some having been immunised five to six
81
R. M. Cullen, W. J. Walker, ‘Measles epidemics 1949-91: the impact of mass immunisation in New
Zealand’, NZMJ, 109, 1039, 1996, p.400.
82
I. R. B. Hardy, D. R. Lennon, E. A. Mitchell, ‘Measles epidemic in Auckland 1984-85’, p.274.
83
MOH Wanganui to Head Office, 20 June 1980, ABQU 632 W4415/345 50984 144/18, ANZ,
Wellington.
84
G. P. Harrison, G. A. Durham, ‘The 1991 measles epidemic: how effective is the vaccine?’, NZMJ,
105, 22 July 1992, p. 280.
85
R. M. Cullen, W. J. Walker, 'Measles epidemics 1949-91’, pp.400-01. The first dose was
administered at 15 months.
216