22 | New Scientist | 6 November 2021
NOT a single case of measles
has been recorded in Australia
this year, a side benefit of the
country shutting its borders
to keep out the coronavirus.
Measles rates have also
plummeted in most other
nations, but experts are worried
that interrupted immunisation
programmes during the crisis
could lead to a resurgence.
Before the covid-19 pandemic,
measles infections in Australia
had been climbing in line with
global trends. In 2019, the
nation recorded 284 cases – the
most in five years. The majority
were found in people who
caught the virus overseas
and brought it home.
Then, in March 2020,
Australia introduced tight
border controls to try to hold
covid-19 at bay. Citizens have
since been unable to travel
overseas, non-Australians
have been barred from
entrance and all returning
Australians have had to
quarantine upon arrival.
During this time, there has
been a sharp drop in measles
infections in Australia, withjust 25 cases recorded in 2020
and none so far in 2021. Fully
vaccinated Australian citizens
and permanent residents have
been allowed to leave the
country since 1 November.
While the border has been
closed, any existing measles
virus in Australia has “burntitself out” thanks to high
vaccination coverage and no
more has been able to come
in, says David Durrheim at
the University of Newcastle
in Australia. More than 94 per
cent of Australian children are
immunised against the disease.
Measles rates also seem
to have waned in most other
countries, although this is
partly due to under-reporting
by health systems that are
busy dealing with covid-19,
says Kim Mulholland, a
member of the World Health
Organization’s working
group on measles and rubellavaccines who is based
in Melbourne.
Fewer than 5000 measles
cases are currently being
recorded per month worldwide,
compared with more than
100,000 per month during the
peak of the last big measles
outbreak in 2019.
In England, there were
two confirmed measles cases
from January to September
2021, according to figures due
to be released at the end of
November, compared with
797 in the whole of 2019.
In the US, there have been
45 cases in 2021 so far, down
from 1282 in 2019.
This downwards trend
has probably been driven by
reduced travel and limited
social contact during the
pandemic, as well as the
natural boom-and-bust cycle
of measles, says Mulholland.
However, it may not last
long since the pandemic
has also interrupted many
immunisation programmes
around the world, with an
estimated 27 million children
missing out on getting the
measles vaccine in 2020.
“We’ve got a big and growing
immunity gap globally, so
the conditions are perfect
for a post-pandemic measles
catastrophe,” says Durrheim.
“It’s an accident waiting
to happen,” says Mulholland.
Outbreaks of measles have
already sprung up in countries
like Pakistan, Nigeria, India,
Afghanistan, Somalia and the
Democratic Republic of the
Congo, and these could spread
to other nations as international
travel rebounds, he says. ❚Australian airports
have been empty due
to travel restrictionsDiseasesAlice KleinROBE
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of Australian children are
vaccinated against measlesCovid-19 measures mean
zero measles in Australia
A POLICY change by YouTube to
limit the spread of harmful videos
has had the desired effect.
In January 2019, YouTube
said it would no longer suggest
what it deemed to be harmful
videos through its recommendation
algorithm, although it still allowed
those videos to be stored on its
website. Cody Buntain at the New
Jersey Institute of Technology and
his co-authors were sceptical the
approach would have much effect
because links to YouTube are so
ubiquitous across social media.
“I was actually surprised at
the results we found,” he says.
He and his colleagues monitored
shares of 920,000 videos over
the eight months before and
after the policy change.
The researchers looked at three
types of content. Two are considered
harmful by YouTube’s policies:
conspiracy videos and videos posted
by a group of alt-right YouTubers
called the Alternative Influence
Network (AIN), identified by the
Data & Society Research Network
in New York in 2018. The final type
was a control group of videos from
mainstream news channels. They
analysed 827 million tweets and
79 million Reddit posts to see
how many included these videos.
Facebook wasn’t included because
of issues accessing the data – a
limitation the authors acknowledge.
Conspiracy videos known to have
been subject to YouTube’s move
saw a drop in how many times they
were shared on Twitter and Reddit,
as did videos from the AIN.
Mainstream news channel
videos saw an increase in shares
outside YouTube – indicating that
the policy change worked
(Proceedings of the ACM on
Human-Computer Interaction,
doi.org/g34j). However, less
overtly harmful conspiracy videos
not targeted by YouTube saw an
increase in reach off the platform. ❚Social mediaChris Stokel-WalkerYouTube algorithm
stopped harmful
videos spreading
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