The Australian Immunisation Handbook 10th Edition 2013

communities reported laboratory-confirmed cases of A(H1N1)pdm09 (pH1N1)
influenza, including more than 18 000 deaths. 14 In Australia, a total of 44 403
confirmed cases of pH1N1 influenza occurred between May 2009 and November
2010, including 6767 cases in 2010. A total of 213 pandemic influenza-associated
deaths were reported, 22 of which occurred in 2010. 15
Evidence from multiple outbreak sites demonstrated that the A(H1N1)pdm09
virus rapidly established itself and was the dominant influenza strain in most
parts of the world. The clinical picture of pH1N1 influenza appeared to be largely
consistent across all countries, with most affected persons experiencing moderate
illness. Risk factors for severe disease included obesity, pregnancy, diabetes
mellitus and, in Australia, being of Aboriginal or Torres Strait Islander descent
(see 3.1 Vaccination for Aboriginal and Torres Strait Islander people). Although
influenza can cause very severe and fatal illness, particularly in the elderly, the
impact of pH1N1 influenza in younger healthy adults and in pregnant women
was proportionally greater than normal seasonal outbreaks, even though the
absolute number of such cases remained low. During the last quarter of 2009,
Australia introduced a non-adjuvanted, inactivated, egg-derived, monovalent
A(H1N1)pdm09 vaccine for administration to all persons aged ≥6 months
(Panvax, CSL Limited). Expired monovalent vaccine supplies were withdrawn
in December 2010. 16 In Australia, there was ongoing summer activity of A(H1N1)
pdm09 in late 2009, and the virus continued to circulate in 2010 and 2011,
replacing the previously circulating seasonal H1N1 strain. 2 The A(H1N1)pdm09
strain was included in trivalent seasonal influenza vaccine formulations used in
the southern hemisphere in 2010, 2011 and 2012.
4.7.4 Vaccines
The administration of influenza vaccine to persons at risk of complications of
infection is the single most important measure in preventing or attenuating
influenza infection and preventing mortality. After vaccination, most adults
develop antibody levels that are likely to protect them against the strains of
virus represented in the vaccine. In addition, there is likely to be protection
against many related influenza variants. Infants, the very elderly, and persons
who are immunocompromised may develop lower post-vaccination antibody
levels. Under these circumstances, influenza vaccine may be more effective
in preventing lower respiratory tract involvement or other complications of
influenza than in preventing influenza infection.
246 The Australian Immunisation Handbook 10th edition