8 | New Scientist | 15 August 2020
a strategy is a very inexact science.
A team led by Emma McBryde at
James Cook University in Australia
has started modelling possible
scenarios, but the results are still
under wraps. One thing we can say,
however, is that ring vaccination
isn’t going to work. Ebola is
transmitted by contact with bodily
fluids, so spreads relatively slowly,
whereas covid-19 is a respiratory
disease that spreads very rapidly.
Regardless of the specifics,
the overwhelming rationale
for introducing any new vaccine
is to reduce severe illness and
mortality. That holds true for
covid-19. But there are other
considerations, says Nicholas
Grassly, a vaccine epidemiologist
at Imperial College London who
sits on the Strategic Advisory
Group of Experts covid-19 vaccine
group for the World Health
Organization (WHO) but spoke
to New Scientist in a personal
capacity. “Vaccination for covid-
is not just about health, it is aboutIT IS August 2021, and the
moment the world has been
waiting for has finally arrived.
After many false dawns,
a vaccine against covid-
has passed all the tests
and is ready to be rolled out.
It has been an arduous journey,
but at last vaccine manufacturers
around the world are cranking out
thousands of doses a day. The end
of the pandemic is on the horizon.
But this isn’t the end. It isn’t
even the beginning of the end.
There are more than 7.5 billion
people in need of vaccination
but perhaps only a billion
doses available in the first
six months of production.
Who gets one? Everyone agrees
that front-line healthcare workers
must be first in the queue. But who
should be next? What is the best
way to attain herd immunity? Will
people accept the vaccine? And is
it possible to stop rich countries
from hoarding the supplies?
The answers to these questions
depend largely on decisions being
made now, in 2020, long before
a successful vaccine has been
developed. Of course, that day may
never arrive. But let us assume
that it does. What happens next?No single approach
Even if a vaccine works, there is
no one-size-fits-all vaccination
regime. The two newest vaccines
to be developed give a flavour of the
problem facing epidemiologists.
These are the Ebola vaccine
Ervebo, approved in November
2019, and a dengue fever vaccine
Dengvaxia, approved in 2015.
Consider Ervebo. Before covid-
19 stalled its roll-out there was
enough time to devise and test
containment strategies. These
show that the most effective
approach is ring vaccination. That
means tracking down confirmedEthicsKIRSTY^ WIGGLE
SWORTH
/AP/SHUTTE
RS
TOCKWho gets to have the vaccine?
If a covid-19 vaccine is finally developed, tough decisions await about who
should be first in line for the limited initial supply, says Graham LawtonNews Coronavirus
50 million
Healthcare workers – doctors,
community health workers,
nurses and midwives – are the
first priority for vaccinations1.1 billion
High-risk adults, with
conditions such as
diabetes, cardiovascular
disease, cancer or obesity,
are third in the queue600 million
Adults over the age of 65,
making up 8 per cent of the
global population, are the
second priorityWho will get a vaccine,
and when, according
to the World Health
Organization’s strategySOURCE: WORLD HEALTH ORGANIZATIONcases and vaccinating all of their
contacts and all of their contacts’
contacts, thus throwing a ring of
immunity around the virus.
For Dengvaxia, however, the
most effective strategy depends
on local circumstances. When the
virus is rampant, mass vaccination
offers the most protection to the
largest number of people. But
where transmission rates are
lower, it is better to selectively
vaccinate adults who have already
had the virus. This is because a
second bout is more dangerous
than the first one due to the way
the immune system ratchets up.
That also means that vaccinating
infants, who are unlikely to have
had the virus, can backfire because
the vaccine acts like a first bout.
So what works for one disease
might be less than optimal for
another, because diseases and
vaccines are all different. For
covid-19, the absence of both a
vaccine and full understanding of
the disease means that designing