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two B viruses, does seem to be a good fit.
However, choosing which strains to target
is no easy task. Twice a year, in February/
March for the Northern Hemisphere and
September/October for the Southern, the
World Health Organisation (WHO) amasses
data from a growing armoury of global
surveillance, virus analysis and antigenic
mapping techniques to decide which
viruses should be included in the seasonal
vaccines for that year.
“But the problem with vaccine-strain
selection is the time it takes to manufacture
a vaccine – between 5-6 months,” says
virologist Lance Jennings. By the time the
vaccine is distributed and gets into people’s
arms, the circulating virus may have already
evolved through a process called antigenic
drift, in which slight mutations in the flu-
virus proteins allow it to evade the human
immune system. “So, you make a decision
as to the most likely viruses that are going to
be circulating – for us, that decision is made
in October each year,” says Jennings. “That
virus then has a whole Northern Hemisphere
winter to circulate, and it does evolve. We
are getting better at predicting this, on the
basis of what viruses have been circulating
previously and whether the general
population has an immunity to
prominent strains. But often a virus
pops up from left field and catches
you unaware. We have had two
very mild influenza seasons,but working in this field you are always
expecting the unexpected. We haven’t had
a bad H3N2 year for several years, but this
year is a bad year and continues to be.”THE KILLER IN OUR MIDST
Understanding just how bad is a further
hurdle in our ongoing fight against the
virus. Influenza can increase the risk of
complications such as pneumonia or
respiratory failure, but it has also been found
to have a role in strokes and heart attacks.
A report, published in the New England
Journal of Medicine last year, identified 364
hospitalisations for acute heart attacks
occurring within a year before and a year
after a positive test result for influenza.
“The main process causing the damage
is inflammation,” says Michael Baker. “It
is inflammation that makes platelets more
sticky, for example, or your heart might be
pumping a bit higher and faster because you
have a fever. Your body cannot cope with
the additional stress of that infection and
you die prematurely, whereas you might
have been able to carry on for many more
winters.”
Many regions are reporting mainly single-
figure mortality rates from this year’s flu
season, but only a small proportion (an
estimated one in 23) of deaths caused
directly or indirectly by the flu virus
are recognised and recorded on death
certificates. Michael Baker puts the blame on
our system of recording mortalities. These
tend to prioritise one cause of death. If there
is an underlying condition that is fatally
aggravated by the virus – and once you get
to 65, says Baker, half the population has an
underlying condition of some sort – it is that
condition, rather than flu, that is recorded.
“So, the underlying cause of death might
be coronary disease or prostate cancer, but
if we had stopped the influenza circulating
you might have had another five years.”
With another month of winter to go,
and the usual tail of spring-time respiratory
illnesses to contend with, data is already
being collected to devise a vaccine to limit
the effect of next year’s flu strains.
“Can we predict next year? Unfortunately
not,” says Nick Baker. “In broad terms, to
get two really bad seasons back to back is
less common but not impossible. Flu evolves
from year to year – if we have the same strains
next year, we’ll probably get a milder season.
If something new crops up in this Northern
Hemisphere winter, then we’ll be at the
mercy of whatever new bug comes south.” l20-year-old Zae Wallace, a promising rugby
league player, was the third person in the
region to die from a flu-related illness.
These tragedies, as well as the early start
to the Ministry of Health vaccine campaign
and Australia’s woeful winter (more than
300 flu-related deaths have been confirmed
across the country, three times as many as
in the whole of last year’s flu season), all
helped to push up demand for the flu jab.
Pharmac director of operations Lisa
Williams says the total anticipated supply
of this year’s flu vaccine, as decided last
November, was 1.355 million doses. “The
actual volume of influenza vaccine brought
to New Zealand by the Pharmac contracted
supplier in 2019 was 1.1 million doses.” But
instead of the usual plateau in late May,
demand continued to grow and stockists
were warning of dwindling supplies. GPs
and pharmacists were asked to prioritise
those eligible for publicly funded vaccines
- pregnant women, those aged 65 and over,
children four years and under with serious
respiratory illnesses and people with certain
health conditions.
This month, the Ministry of Health
acquired an additional 55,000 doses of
the influenza vaccine FluQuadri. A further
14,000 doses of Afluria Quad vaccine,
originally intended for the private market,
were made available to those eligible for
publicly funded vaccines.
Overall, says Williams, 1.38 million doses
of influenza vaccine will be distributed
into the community in 2019. “This is the
highest number of influenza vaccine doses
distributed in an annual immunisation
programme.”
EVOLVING THREAT
Vaccines tend to have about 50% to 60%
effectiveness, but this year’s vaccine, a
quadrivalent injection targeting two strains
of influenza type A (H1N1 and H3N2) and
Clockwise from top left: Michael Baker, Trang
Khieu, Nick Baker, Lance Jennings, Lisa Williams
and David Meates.