2020
New study shows COVID-19 measures such as school closures and `high-
traffic and mixing' areas had the strongest association, providing clues for new intervention approaches

Date:
March 3, 2022
Source:
London School of Hygiene & Tropical Medicine
Summary:
A new study shows that COVID-19 measures such as school closures
and 'high-traffic and mixing' areas had the strongest association,
providing clues for new intervention approaches. Nearly three
quarters of a million fewer global cases of dengue occurred in
2020, which could be linked to COVID-19 disruptions limiting human
mobility and contact, according to a new study.



FULL STORY ========================================================================== Nearly three quarters of a million fewer global cases of dengue occurred
in 2020, which could be linked to COVID-19 disruptions limiting human
mobility and contact, according to a new study published in Lancet
Infectious Diseases.


========================================================================== Researchers from the London School of Hygiene & Tropical Medicine (LSHTM), Beijing Normal University and other international partners, funded by
the Medical Research Council, analysed the monthly dengue cases from
the World Health Organization (WHO) Weekly reports between 2014 to 2020
from 23 countries -- 16 in Latin America and seven in South East Asia,
the main regions where dengue is endemic, as well as climate data on
air temperature, relative humidity and precipitation.

They found a strong association between school closures and declines in
non- residential trips, such as shopping or using public transport, due
to COVID-19 and reduced risk of dengue transmission. This indicates that
places such as schools and commonly visited public areas could be dengue transmission hot spots and play a key role in spreading the disease.

Further research is needed into how human movement behaviours (the
places people visit, how long they spend there and with whom) impact
dengue transmission risk. This could help decision makers decide if
measures like contact tracing, testing or quarantine could help control
the spread of the disease.

Dr Oliver Brady, Associate Professor and MRC Fellow at LSHTM and study
senior author, said: "Currently dengue control efforts are focused on
or around the households of people who get sick. We now know that, in
some countries, we should also be focusing measures on the locations
they recently visited to reduce dengue transmission. For all the harm
it has caused, this pandemic has given us an opportunity to inform new interventions and targeting strategies to prevent dengue." Dengue is a
viral infection transmitted by the Aedes species of mosquitoes, which
causes flu-like symptoms. It is found in tropical and sub-tropical
climates worldwide, and is most common in urban areas.



==========================================================================
It is one of the only infectious diseases to show a sustained increase in
cases each year, and the WHO now estimates that around half the world's population is at risk of contracting dengue.

Transmission is closely linked to the weather, surrounding environment
and human mobility. It is also closely associated with the climate, with
hot and humid tropical climates ideal for transmission. Dengue season
in many countries occurs around June to September, when peaks in cases
can cause overcrowding in hospitals -- much like with COVID-19.

Dengue is only spread from mosquito to human and vice versa, and is not transmitted from humans to other humans. However, changes in people's
movements and behaviour may have an effect on transmission, for example
through reduced exposure to mosquitoes or fewer opportunities for infected people to go out and about and pass on the virus to uninfected mosquitoes present there. COVID-19 and the restrictions on human movement that were imposed during the pandemic therefore provide a unique opportunity
to explore how human movement and behaviour contribute to dengue
transmission.

Dengue case numbers suddenly began to decline in April 2020 in many
countries, following the introduction of public health and social
measures targeting the spread of COVID-19 and the resulting change in
human movement and shift to more time spent in residential places. In
2020, dengue cases decreased by 40.2% in Latin America and 58.4% in South
East Asia, with just over two million cases recorded in the Americas
and South East Asia in 2020.

However, unravelling the impacts of COVID-19 disruption is complex as 2019
saw the largest global dengue outbreak in history, with more than 5.2
million cases recorded in the Americas and South East Asia region. This
led to high levels of immunity which would also be expected to reduce
dengue cases in 2020.



==========================================================================
Dr Brady added: "Before this study, we didn't know whether COVID-19
disruption could increase or decrease the global burden of dengue. While
we could assume reduction in human movement would reduce the virus transmission, it would also disrupt the mosquito control measures already
in place. This disruption may result in long-term impacts on dengue cases
which might not be evident until the next epidemic." The research team
looked at two different measures of COVID-19 related disruption -- public health and social measures, such as school and public transport closure, stay-at-home requirements, gathering restrictions; and human movement
behaviour through time spent at residential and public locations. They
also accounted for the different strengths of restrictions in lockdowns
in different countries around the world.

By combining all this data and analysing trends, they were able to show
that reduced time spent in public areas was closely associated with
reduced dengue risk.

Nine out of 11 countries in Central America, the Caribbean and the
Philippines saw a complete suppression of their 2020 dengue season, with
other countries experiencing a much reduced season. In countries where
the COVID-19 restriction measures began at the peak of dengue season,
there was a sharper than expected decline in cases, despite above average incidence being recorded earlier in the year.

This decrease in cases could also be attributed to reduced rates in
people seeking treatment, a higher potential for misdiagnosis and
reduced availability for laboratory testing for dengue could result in misdiagnosis. However, some countries such as Sri Lanka predicted this
could be a problem at the start of the pandemic, so undertook outreach
work to encourage people to get diagnosed and seek treatment. Despite
this, there was no change in rates of severe cases and deaths reported, suggesting the reduction in treatment seeking was not the cause for the reduction in cases.

A better understanding of how treatment-seeking behaviours change during
an epidemic is needed, as access to care and rapid diagnostics change
in order to fully assess and interpret the change in case numbers. The
team emphasises the need for longer term, more routine measurement of
the prevalence of dengue within each population.

Although overall cases declined in 2020, Peru and Singapore reported
worse than average dengue incidence in 2020. This could have occurred due
to the unpredictable natural year-to-year variation in dengue incidence
that occurs due to, for example, the emergence of different dengue virus variants, or could hint at the greater role being bitten by mosquitoes
at home plays in spreading dengue in these countries.

As the climate recorded in 2020 was similar to the average climate of
the last six years, the researchers did not find an association between
climate and the reduction in dengue risk during 2020.

The researchers note that it remains to be seen how many of the estimated
0.72 million cases were truly averted, or just delayed until later years
as human movement returns to pre-COVID levels and say it's key to continue monitoring dengue trends in 2022 and beyond.

The researchers acknowledge the limitations of this study, including lack
of data on the different types of dengue, which can drive outbreaks,
and the potential changes in dengue reporting resulting from COVID-19 disruptions.


========================================================================== Story Source: Materials provided by London_School_of_Hygiene_&_Tropical_Medicine. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Yuyang Chen, Naizhe Li, Jose' Lourenc,o, Lin Wang, Bernard
Cazelles, Lu
Dong, Bingying Li, Yang Liu, Mark Jit, Nikos I Bosse, Sam Abbott,
Raman Velayudhan, Annelies Wilder-Smith, Huaiyu Tian, Oliver J
Brady, Simon R Procter, Kerry LM Wong, Joel Hellewell, Nicholas
G Davies, Christopher I Jarvis, Ciara V McCarthy, Graham Medley,
Sophie R Meakin, Alicia Rosello, Emilie Finch, Rachel Lowe, Carl
A B Pearson, Samuel Clifford, Billy J Quilty, Stefan Flasche,
Hamish P Gibbs, Lloyd A C Chapman, Katherine E.

Atkins, David Hodgson, Rosanna C Barnard, Timothy W Russell,
Petra Klepac, Yalda Jafari, Rosalind M Eggo, Paul Mee, Matthew
Quaife, Akira Endo, Sebastian Funk, Ste'phane Hue', Adam J
Kucharski, W John Edmunds, Kathleen O'Reilly, Rachael Pung,
C Julian Villabona-Arenas, Amy Gimma, Kaja Abbas, Kiesha Prem,
Gwenan M Knight, Fiona Yueqian Sun, William Waites, James D Munday,
Mihaly Koltai, Frank G Sandmann, Damien C Tully.

Measuring the effects of COVID-19-related disruption on dengue
transmission in southeast Asia and Latin America: a statistical
modelling study. The Lancet Infectious Diseases, 2022; DOI:
10.1016/S1473-3099 (22)00025-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220302190011.htm

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