Faculty of Medicine and Health

PUBLIC HEALTH Citizen science
is helping to map snakebite
risk p.478
ENVIRONMENT A call to safeguard
biodiversity in regions of
armed conflict p.478
POLITICS How Hindu
nationalists have co-opted
the trappings of science p.476
BIAS Why do racial
stereotypes persist
in sport? p.474
T housands of people worldwide have
been affected by recent measles
outbreaks, even though there is a
safe and effective vaccine.
In the first four months of this year, the
World Health Organization (WHO) reported
about 226,000 measles cases — almost three
times the count recorded in the same period
last year (see go.nature.com/2jkq8d3).
Already, the number of cases in the United
States this year has exceeded the reported
tally in any year since the country halted
sustained transmission of the disease in
2000. Similarly, in Europe, the 2018 figures
were the highest this decade (see ‘Measles
on the rise’).
Partly in response to these outbreaks,
some governments are now considering
making vaccination for measles and other
diseases a legal requirement 1 . The state of
New York signed legislation to that effect
last month.
Such mandates, which began with small-
pox vaccination in nineteenth-century
Europe, are in place for numerous vaccines
in various countries. And several studies
show that requiring vaccination can
Mandate vaccination with care
Governments that are considering compulsory immunizations must avoid stoking
anti-vaccine sentiment, argue Saad B. Omer, Cornelia Betsch and Julie Leask.
Children with measles in an overcrowded hospital ward in the Philippines, where an outbreak occurred in Manila and central Luzon in February 2019.
FRANCIS R. MALASIG/EPA-EFE/SHUTTERSTOCK
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improve rates in high-income countries
(see, for example, ref. 2), although there
is limited evidence of the impact of such
requirements in low- or middle-income
nations.
However, mandatory vaccination can
worsen inequities in access to resources,
because penalties for not complying can
disproportionately affect disadvantaged
groups. What’s more, the evidence suggests
that there is no simple linear relationship
between the forcefulness of a policy and its
impact on the rate of vaccination.
It is crucial that policies don’t inadvert-
ently entrench inequity or fuel anti-vaccine
activism. As specialists in vaccination
policy and programmes, we lay out here
what’s known, to help governments con-
sider whether a mandate is the right fit for
their situation. We also discuss what other
changes should be made before introduc-
ing requirements (see ‘Best practice’). And
we distil how mandates should be designed
to ensure effectiveness.
WHICH MANDATES WORK?
There has long been substantial variability
in how governments and jurisdictions
mandate vaccination — specifically, in
what is actually required of people; the
penalties imposed if requirements are not
met; and the age groups and populations
that are covered.
In the United States, for instance, proof
of immunization or exemption documen-
tation is required before children can go to
school. All 50 states and Washington DC
allow exemptions for medical reasons, and
45 states allow philosophical or religious
exemptions. In Australia, certain vaccines
are a requirement for entry into preschool
or childcare in some states, but not in
others. In Uganda, parents who fail to vac-
cinate their children can be jailed for six
months.
Studies conducted largely in the United
States and Europe suggest that making vac-
cination a requirement for enrolment in
childcare and school can help to increase
rates (see, for example, ref. 2). For instance,
a review of studies conducted mostly in the
United States found that the need to pro-
vide documentation to access childcare or to
attend school and college is associated with
a median improvement of 18 percentage
points in the rate of vaccination for diseases
such as measles, hepatitis B and whooping
cough (see go.nature.com/3tzrujo).
When it comes to obtaining an exemption,
having complex administrative procedures
in place (such as those involving counsel-
ling with a physician) reduces the number of
parents who refuse to have their children vac-
cinated. It also lowers the number of people
who are affected by vaccine-preventable
diseases 2 . In a 2012 study, non-medical
exemption rates were more than twice as
high in US states that had relatively easy
exemption procedures, compared with states
that had more complex ones3
.
Given such evidence, governments have
sometimes removed non-medical exemp-
tions altogether. In the past four years, the
states of Maine,
New York and Cali-
fornia joined West
Virginia and Mis-
sissippi in eliminat-
ing non-medical
exemptions for all
or some vaccines.
And in response
to a media and
public campaign,
Australia implemented legislation in 2016
that prevents parents from obtaining
non-medical exemptions.
Increases in vaccination rates have been
associated with financial penalties. These
take the form of either the withdrawal of
family assistance payments (currently as
much as Aus$26,000 (US$18,200) a year
in Australia, by our calculations) or fines
for parents who refuse to vaccinate their
children. In a study evaluating mandatory
vaccination in Europe, measles vaccine
coverage was 0.8% higher and whooping-
cough vaccine coverage was 1.1% higher
for every €500 (US$560) increase in the
penalty 4 .
Vaccination requirements (tied to school
and childcare access, or to monetary pen-
alties) fare well in comparisons with other
large-scale interventions, such as vaccina -
tion drives at schools, or communication
campaigns involving pamphlets, billboards,
television advertisements and so on. A 2017
review of interventions to increase vaccina-
tion found that in high-income countries,
requirements to vaccinate are more likely to
affect rates than are attempts to change how
people think and feel about vaccination 5 .
EXEMPTIONS AND PENALTIES
So, in many cases, requirements to vaccinate
do seem to improve vaccination rates. But
do rigid, punitive policies work better than
flexible ones? In our view, not necessarily.
In fact, the limited data that are available
suggest that a middle-of-the-road approach
might be more effective. These data come
mainly from California, Washington state
(which eliminated personal-belief exemp-
tions to measles, mumps and rubella (MMR)
vaccination this year) and Australia.
In 2015, California became the third US
state to eliminate all non-medical exemp-
tions, and the first state to do so in more
than three decades. This change in the law
was preceded by a 2014 administrative
initiative to reduce the misuse of a school
admission process involving ‘conditional
entrants’ — children who have started the
required vaccination schedule but haven’t
completed it 6 . (Since 1979, children in Cal-
ifornia have been allowed to attend school
as conditional entrants — but before 2014,
only some schools followed up with par-
ents, and some children were never fully
vaccinated 6 .)
The proportion of children of kinder-
garten age who are not up to date on their
vaccinations has decreased in California,
from 9.8% in 2013 to 4.9% in 2017 (ref. 7).
However, this change seems to be mainly
associated with the administrative crack-
down on conditional entrants. Following
the elimination of non-medical exemp-
tions, many parents with strong objections
to vaccination simply acquired medical
exemptions instead, educated their chil-
dren at home, enrolled them in independ-
ent study programmes that do not require
classroom-based instruction, or found
other loopholes 6 .
In Australia, following policy changes in
1999, parents had to get their child vacci-
nated to get assistance payments. And they
could obtain non-medical exemptions only
after they had discussed the issue with a
health-care provider. According to surveys,
these policies helped to improve vaccina-
tion coverage from an estimated 80% to
more than 90% in three years 8 .
Then, in 2016, Australia implemented
a ‘No Jab No Pay’ policy, which removed
non-medical exemptions and applied the
“There is no
simple linear
relationship
between the
forcefulness
of a policy
and its impact
on the rate of
vaccination.”
SOURCE: WHO
4 7 0 | N A T U R E | V O L 5 7 1 | 2 5 J U L Y 2 0 1 92015 2017 2019 †20132011Measles cases (hundreds of thousands)01234AfricanAmericas *Eastern MediterraneanEuropeanSoutheast AsiaWestern Paci cMEASLES ON THE RISELarge outbreaks have occurred worldwidesince 2017 despite there being a safe andeffective vaccine.*Key refers to World Health Organization regions. †To June.
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