Nationwide Surveillance of Influenza during the Pandemic (2009–10) and Post-Pandemic (2010–11) Periods in Taiwan

INTRODUCTION: Although WHO declared the world moving into the post-pandemic period on August 10, 2010, influenza A(H1N1) 2009 virus continued to circulate globally. Its impact was expected to continue during the 2010-11 influenza season. This study describes the nationwide surveillance findings of the pandemic and post-pandemic influenza periods in Taiwan and assesses the impact of influenza A(H1N1) 2009 during the post-pandemic period. METHODS: The Influenza Laboratory Surveillance Network consisted of 12 contract laboratories for collecting and testing samples with acute respiratory tract infections. Surveillance of emergency room visits and outpatient department visits for influenza-like illness (ILI) were conducted using the Real-Time Outbreak and Disease Surveillance system and the National Health Insurance program data, respectively. Hospitalized cases with severe complications and deaths were reported to the National Notifiable Disease Surveillance System. RESULTS: During the 2009-10 influenza season, pandemic A(H1N1) 2009 was the predominant circulating strain and caused 44 deaths. However, the 2010-11 influenza season began with A(H3N2) being the predominant circulating strain, changing to A(H1N1) 2009 in December 2010. Emergency room and outpatient department ILI surveillance displayed similar trends. By March 31, 2011, there were 1,751 cases of influenza with severe complications; 50.1% reported underlying diseases. Of the reported cases, 128 deaths were associated with influenza. Among these, 93 (72.6%) were influenza A(H1N1) 2009 and 30 (23.4%) A(H3N2). Compared to the pandemic period, during the immediate post-pandemic period, increased number of hospitalizations and deaths were observed, and the patients were consistently older. CONCLUSIONS: Reemergence of influenza A(H1N1) 2009 during the 2010-11 influenza season had an intense activity with age distribution shift. To further mitigate the impact of future influenza epidemics, Taiwan must continue its multifaceted influenza surveillance systems, remain flexible with antiviral use policies, and revise the vaccine policies to include the population most at risk

Population-Based Evaluation of Vaccine Effectiveness against SARS-CoV-2 Infection, Severe Illness, and Death, Taiwan

Taiwan provided several COVID-19 vaccine platforms: mRNA (BNT162b2, mRNA-1273), adenoviral vector-based (AZD1222), and protein subunit (MVC-COV1901). After Taiwan shifted from its zero-COVID strategy in April 2022, population-based evaluation of vaccine effectiveness (VE) became possible. We conducted an observational cohort study of 21,416,151 persons to examine VE against SARS-CoV-2 infection, moderate and severe illness, and death during March 22, 2021–September 30, 2022. After adjusting for age and sex, we found that persons who completed 3 vaccine doses (2 primary, 1 booster) or received MVC-COV1901 as the primary series had the lowest hospitalization incidence (0.04–0.20 cases/100,000 person-days). We also found 95.8% VE against hospitalization for 3 doses of BNT162b2, 91.0% for MVC-COV1901, 81.8% for mRNA-1273, and 65.7% for AZD1222, which had the lowest overall VE. Our findings indicated that protein subunit vaccines provide similar protection against SARS-CoV-2­­–associated hospitalization as mRNA vaccines and can inform mix-and-match vaccine selection in other countries

Incidence of influenza hospitalized cases with severe complications stratified by age and virus subtype in Taiwan, week 26, 2010–week 13, 2011.

<p>Incidence of influenza hospitalized cases with severe complications stratified by age and virus subtype in Taiwan, week 26, 2010–week 13, 2011.</p

Percentages of influenza-like illness (ILI) visits in emergency room (ER) and outpatient department (OPD), week 26, 2009–week 25, 2011.

<p>Percentages of influenza-like illness (ILI) visits in emergency room (ER) and outpatient department (OPD), week 26, 2009–week 25, 2011.</p

Comparisons of numbers of influenza A(H1N1) 2009 cases with severe complications and deaths between 2009–10 and 2010–11 seasons (as of March 31, 2011)^*.

*<p>2009–10 season: from week 26, 2009 to week 25, 2010; 2010–11 season: from week 26, 2010 to week 13, 2011.</p

Number of influenza-associated deaths by week of onset in Taiwan, week 26, 2010–week 13, 2011.

<p>Number of influenza-associated deaths by week of onset in Taiwan, week 26, 2010–week 13, 2011.</p

Respiratory specimen testing influenza positive rates in Taiwan, week 26, 2009–week 13, 2011.

<p>Respiratory specimen testing influenza positive rates in Taiwan, week 26, 2009–week 13, 2011.</p

Comparisons of numbers of influenza A(H1N1) 2009-associated outpatient department (OPD) visits between 2009–10 and 2010–11 seasons (as of week 13, 2011)^*.

*<p>2009–10 season: from week 26, 2009 to week 25, 2010; 2010–11 season: from week 26, 2010 to week 13, 2011.</p