Weekly updates, Influenza Epidemiological Week 25 (30 June 2023)

North America: Influenza activity has remained at low levels. During the last 4 epidemiological weeks (EW), the predominant influenza viruses have been B/Victoria, with a lesser circulation of influenza A (mostly A(H1N1)pdm09). Respiratory syncytial virus (RSV) activity has remained low. The activity of SARS-CoV-2 has shown a slight increase and continues to circulate at moderate levels. Cases of influenza-like illness (ILI) and severe acute respiratory infection (SARI) have shown a decreasing trend, with the majority of these cases associated with SARS-CoV-2 and to a lesser extent influenza.

Caribbean: Influenza activity has shown a decreasing trend. During the last 4 EWs, the predominant influenza viruses have been B/Victoria, with lesser circulation of influenza A (mainly A(H1N1)pdm09). RSV activity has remained low. SARS-CoV-2 activity has increased in the last 4 weeks and is currently at intermediate levels of circulation. Cases of ILI and SARI have shown an increase due to positive SARS-CoV-2 cases and to a lesser extent influenza cases.

Central America: Influenza activity has shown a pronounced increase in the last 4 EW with high levels of circulation. During the last 4 EWs, the predominant influenza viruses have been influenza A, mainly A(H1N1)pdm09, with co-circulation of influenza A(H3N2) and influenza B/Victoria to a lesser extent. RSV activity has remained low. SARS-CoV-2 activity has remained low and has decreased in recent weeks. The incidence of ILI has remained low, with the majority of cases associated with influenza and SARS-CoV-2.Although SARI activity is currently declining, there has been an increase in the past four weeks, with the majority of cases attributed to influenza, and to a lesser extent, RSV and SARS-CoV-2. In Costa Rica, extraordinarily high levels of influenza positivity have been observed, coinciding with the concurrent circulation of SARS-CoV-2. However, the levels of ILI and SARI have remained low, with the majority of cases linked to influenza and, to a lesser extent, SARS-CoV-2. Honduras has experienced exceptionally high levels of influenza positivity in recent weeks, with moderate levels of SARI cases showing a declining trend, all of these due to influenza. Nicaragua and Panama have also seen an increase in influenza positivity in recent weeks, reaching moderate levels of intensity in both countries and currently declining. Guatemala has presented an increase in RSV activity, with ILI and SARI activity surpassing the epidemic threshold. Most ILI cases are associated with SARS-CoV-2, while SARI cases are primarily linked to RSV and influenza.

Andean region: Influenza activity remains stable at low levels. During the last 4 EW, the predominant influenza viruses have been influenza A, mostly A(H1N1)pdm09, with lesser circulation of influenza B/Victoria. RSV activity has shown a decrease, remaining at low levels of circulation. SARS-CoV-2 has shown an increase, circulating at moderate levels. The incidence of SARI cases has exhibited a slight rise, primarily attributed to influenza cases, with lesser contributions from RSV and SARS-CoV-2. ILI activity has shown a decreasing trend, with the majority of cases associated with influenza. In Ecuador, high levels of SARI associated with influenza, as well as to a lesser extent with SARS-CoV-2 and RSV, have been detected.

Brazil and Southern Cone: Influenza activity has decreased to low levels of circulation. Over the past 4 EWs, the predominant influenza viruses have primarily been A(H1N1)pdm09, with simultaneous circulation of influenza B/Victoria virus. RSV activity has declined in the last three EWs, reaching moderate levels of circulation. SARS-CoV-2 activity has remained low. Following a peak, both SARI and ILI activity have decreased in the past 4 EWs, with the majority of positive cases attributed to RSV and influenza in SARI cases, and influenza in ILI cases. In Argentina, a pronounced increase in influenza activity has been observed, reaching medium-high levels, with the majority of cases detected as influenza A(H1N1)pdm09 and epidemic levels in ILI cases. In Chile, extraordinary levels of ILI activity have been observed, with the majority of cases related to RSV and influenza. This activity has decreased in the past weeks and is currently at moderate levels. Moderate levels of SARI activity have also been detected in Chile in the past 4 epidemiological weeks, with RSV being the most common cause among positive cases. This activity has also decreased in the last week and is currently at epidemic levels. In Paraguay, an extraordinary level of SARI activity has been observed, currently decreasing, with RSV being the main cause among positive cases, followed by influenza and to a lesser extent, SARS-CoV-2. In Uruguay, an increase in SARI activity has been detected, reaching moderate levels, with the majority of cases associated with RSV and influenza.