Re-emergence of influenza Virus Circulation during 2020 in parts of
Tropical Asia: Implications for Other Countries
Abstract
Global influenza virus circulation declined and has been below
traditional seasonal levels during the COVID-19 pandemic.1-3 We reviewed
WHO influenza surveillance outputs from May 1-December 31, 2020
(epidemiologic weeks 18-53) from tropical Asian countries. For each
country we report influenza surveillance specimens tested, and the
percentage positive for influenza, by type and subtype. We compared
current data to historical data from 2015-2019 in order to place the
current season in historical context. Twelve included countries tested
17,407 surveillance specimens, with 592 (3.4%) testing positive for
influenza viruses. From April 27-July 26, 2020 (epidemiologic weeks
18-30), specimens tested decreased from an average of 14,102 per year in
2015-2019 to 3,969 (71.9% decrease) and influenza positivity from 22%
to <1%. During weeks 31-53, specimens tested decreased from
an average of 24,782 per year in 2015-2019 to 13,438 (45.8% decrease)
and influenza positivity from 18% to 4%. In six countries that
maintained testing of surveillance specimens for >90% of
weeks, influenza circulation was unseasonably low, or absent, during
weeks 18-30, 2020. However, during weeks 31-53, the percentage of
surveillance specimens testing positive for influenza approached or
reached positivity rates of 2015-2019 in Bangladesh and Cambodia; and
increased but remained lower than historical positivity in Lao PDR and
Viet Nam. The data presented here are a reminder that the low levels of
influenza circulation in the northern hemisphere in summer 2020 may not
necessarily persist into the upcoming influenza season, and influenza
surveillance and prevention strategies should continue as planned and
not be delayed.