Respiratory Viruses Surveillance Bulletin: Epidemiological Week 49

Overview

• Influenza positivity has continued to increase in the region and reached 44% in week 49, whilst SARS-CoV-2 positivity continues to be below 5% (Figure 1). The predominant circulating influenza subtype remains influenza A(H3N2) (Figure 2).
• Influenza activity continues to be high in northern hemisphere countries: Brunei Darussalam, Cambodia, China, Japan, Lao PDR, Mongolia and Viet Nam, but is declining in Malaysia, the Philippines, Republic of Korea, and Singapore.
• Unseasonal increases in influenza activity have been observed in some southern hemisphere countries; Fiji, Indonesia, New Caledonia, Tonga and Tuvalu (personal communication). Other Pacific Islands may have high levels of influenza positivity; however, only syndromic data for ILI are available.
• Media reports have indicated school clusters and elevated positivity rates in school age children in China and reductions in incidence in school age children has been noted in the Republic of Korea. 
• On 10 December, the World Health Organization released a Disease Outbreak News update on the global status of seasonal influenza. In summary:
  • Global activity remains within expected seasonal range for this time of year, early increases and higher activity than typical at this time of year have been observed in some countries.
  • A rapid increase across multiple countries has been observed, primarily driven by an emerging subclade of A(H3N2), identified as J.2.4.1 (designated subclade K). Current surveillance data show no evidence of increased severity of illness.
  • Vaccination remains vital, to prevent flu infections, reduce disease severity, hospitalizations and lowers the chance of complications and death, particularly for individuals at higher risk of influenza-related complications and those who care for them. Despite some genetic differences between circulating influenza strains and those included in the current vaccine formulations, seasonal influenza vaccines are still expected to provide protective benefits.