An Intense Out-of-Season Rebound of Influenza Activity After the Relaxation of Coronavirus Disease 2019 Restrictions in Beijing, China.

Background: The aim of this study was to investigate the changes of epidemic characteristics of influenza activity pre- and post-coronavirus disease 2019 (COVID-19) in Beijing, China. Methods: Epidemiologic data were collected from the influenza surveillance system in Beijing. We compared epidemic intensity, epidemic onset and duration, and influenza transmissibility during the 2022-2023 season with pre-COVID-19 seasons from 2014 to 2020. Results: The overall incidence rate of influenza in the 2022-2023 season was significantly higher than that of the pre-COVID-19 period, with the record-high level of epidemic intensity in Beijing. The onset and duration of the influenza epidemic period in 2022-2023 season was notably later and shorter than that of the 2014-2020 seasons. Maximum daily instantaneous reproduction number (Rt) of the 2022-2023 season (Rt = 2.31) was much higher than that of the pre-COVID-19 period (Rt = 1.49). The incidence of influenza A(H1N1) and A(H3N2) were the highest among children aged 0-4 years and 5-14 years, respectively, in the 2022-2023 season. Conclusions: A late, intense, and short-term peak influenza activity was observed in the 2022-2023 season in Beijing. Children <15 years old were impacted the most by the interruption of influenza circulation during the COVID-19 pandemic. Maintaining continuous surveillance and developing targeted public health strategies of influenza is necessary.

The role of absolute humidity in influenza transmission in Beijing, China: risk assessment and attributable fraction identification.

To assess the impact of absolute humidity on influenza transmission in Beijing from 2014 to 2019, we estimated the influenza transmissibility via the instantaneous reproduction number (Rt), and evaluated its nonlinear exposure-response association and delayed effects with absolute humidity by using the distributed lag nonlinear model (DLNM). Attributable fraction (AF) of Rt due to absolute humidity was calculated. The result showed a significant M-shaped relationship between Rt and absolute humidity. Compared with the effect of high absolute humidity, the low absolute humidity effect was more immediate with the most significant effect observed at lag 6 days. AFs were relatively high for the group aged 15-24 years, and was the lowest for the group aged 0-4 years with low absolute humidity. Therefore, we concluded that the component attributed to the low absolute humidity effect is greater. Young and middle-aged people are more sensitive to low absolute humidity than children and elderly.

Using an influenza surveillance system to estimate the number of SARS-CoV-2 infections in Beijing, China, weeks 2 to 6 2023.

With COVID-19 public health control measures downgraded in China in January 2023, reported COVID-19 case numbers may underestimate the true numbers after the SARS-CoV-2 Omicron wave. Using a multiplier model based on our influenza surveillance system, we estimated that the overall incidence of SARS-CoV-2 infections was 392/100,000 population in Beijing during the 5 weeks following policy adjustment. No notable change occurred after the Spring Festival in early February. The multiplier model provides an opportunity for assessing the actual COVID-19 situation.

Role of presymptomatic transmission of COVID-19: evidence from Beijing, China.

BACKGROUND: The presymptomatic transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been documented in limited clusters, and it is predicted through modelling. However, there is a lack of evidence from observations with a large sample size. METHODS: We used data from meticulous contact tracing of people exposed to cases of SARS-CoV-2 to estimate the proportion of cases that result from the presymptomatic transmission of the virus in Beijing during January 2020 and February 2020. RESULTS: The results showed that presymptomatic transmission occurred in at least 15% of 100 secondary COVID-19 cases. The earliest presymptomatic contact event occurred 5 days prior to the index case's onset of symptoms, and this occurred in two clusters. CONCLUSIONS: The finding suggested that the contact tracing period should be earlier and highlighted the importance of preventing transmission opportunities well before the onset of symptoms.

Avian influenza A (H9N2) virus infections among poultry workers, swine workers, and the general population in Beijing, China, 2013-2016: A serological cohort study.

BACKGROUND: Few studies have reported on the seroprevalence of antibodies against avian influenza A (H9N2) virus and the incidence of these infections in the northern China and among swine workers. METHODS: We conducted a serological cohort study among people working with poultry or swine or the general population in Beijing, China. It comprised four cross-sectional serological surveys in November 2013, April 2014, April 2015, and April 2016. Blood samples collected from the participants were tested for anti-H9N2 antibodies using a hemagglutination-inhibition (HI) assay. Multivariable Poisson regression model was then used to compare the person-month incidence rates for H9N2 viral infections among the three groups, assessed by incidence rate ratio (IRR). RESULTS: In the four cross-sectional surveys, the highest seroprevalence of anti-H9N2 antibodies (HI titer ≥ 80) was recorded in the poultry workers (2.77%, 19/685) in April 2016, while the lowest was recorded in the general population (0.09%, 1/1135) in April 2015. The highest incidence density rate for H9N2 infections across the whole study period was recorded among the poultry workers (3.75/1000 person-months), followed by the swine workers (1.94/1000 person-months) and the general population (1.78/1000 person-months). Multivariable analysis showed that the poultry workers were at higher risk (IRR: 2.42, 95% CI: 1.07-5.48; P = 0.034) of contracting H9N2 virus than the general population. CONCLUSIONS: Although the seroprevalence of H9N2 antibodies was low in Beijing, the poultry workers were at higher risk of contracting H9N2 viral infections than the general population. Closer monitoring and strengthened protection measures for poultry workers are warranted.

Reduction of influenza A(H3N2)-associated symptoms by influenza vaccination in school aged-children during the 2014-2015 winter season dominated by mismatched H3N2 viruses.

BACKGROUND: Little is known about the vaccine effectiveness (VE) in attenuating the influenza-associated symptoms in children during the 2014-2015 influenza season in Beijing, China, in which there was a mismatch between the vaccine and circulating strain. METHODS: This study included 210 laboratory-confirmed influenza cases among children, who were enrolled in 2014, from November 1 to December 31. Standard demographic information and clinical symptoms were recorded. Influenza vaccination was confirmed via a vaccination registry. Univariate and multivariate analyses were used to estimate the odds of presenting with clinical symptoms among vaccinated and unvaccinated groups, adjusting for sex, age, area, BMI level, and chronic conditions. RESULTS: Among the 210 laboratory-confirmed influenza cases, 170 (81.0%) presented with fever ≥38°C. The other most common symptoms were cough (78.1%), sore throat (46.7%), nasal congestion/rhinorrhea (38.6%), headache (34.8%), fatigue (24.8%) and myalgia/arthralgia (16.2%). Approximately 9.0% (19/210) exhibited nausea/vomiting, and 2.4% (5/210) exhibited diarrhea/abdominal pain. Respiratory complications occurred in 5.7% (12/210) of the confirmed influenza cases. In 210 laboratory-confirmed cases, univariate and multivariate conducted after adjusted for the aforementioned characteristics suggested that the odds of fever ≥ 38°C were significantly reduced in vaccinated children (odds ratio [OR]: 0.42, 95% CI: 0.19-0.93; P = 0.033). CONCLUSIONS: Influenza vaccination may reduce the clinical symptoms of laboratory-confirmed influenza cases potentially even in the mismatching season.

Influenza vaccine effectiveness in preventing laboratory-confirmed influenza in outpatient settings: A test-negative case-control study in Beijing, China, 2016/17 season.

BACKGROUND: The objective of this study was to estimate influenza vaccine effectiveness (VE) for the 2016/17 epidemic of co-circulating influenza A(H1N1)pdm09 and A(H3N2) viruses in Beijing, the capital of China. METHODS: The surveillance-based study included all swabbed patients through influenza virological surveillance, between November 2016 and April 2017. A test-negative case-control design was used to estimate influenza VE against medically-attended laboratory-confirmed influenza in outpatient settings. Cases were influenza-like illness (ILI) patients who tested positive for influenza, and controls were influenza negative patients. RESULTS: A total of 10,496 ILI patients were enrolled and swabbed. Among them, 735 tested positive for influenza A(H1N1)pdm09, 1851 for A(H3N2), and 40 for type B. Of the 45 randomly selected specimens out of 1851 influenza A(H3N2) viruses, 2(4.4%) belonged to the H3N2 3C.2a1 clade, and 43(95.6%) belonged to A/Hong Kong/4801/2014-like 3C.2a clade. Among the 43 viruses of the 3C.2a clade, 32 viruses clustered in one subgroup carrying T131K, R142K and R261Q substitutions. The adjusted VE against all influenza was low at 25% (95% confidence interval (CI): 0-43%), with 54% (95%CI: 22-73%) for influenza A(H1N1)pdm09, and 2% (95%CI: -35% to 29%) for influenza A(H3N2). CONCLUSIONS: Our study suggested a moderate VE against influenza A(H1N1)pdm09, but low VE against influenza A(H3N2) in Beijing, 2016/17 season. Amino acid substitutions in the hemagglutinin may contribute to the low VE against influenza A(H3N2) for this season.

Moderate influenza vaccine effectiveness against influenza A(H1N1)pdm09 virus and low effectiveness against A(H3N2) virus among older adults during 2013-2014 influenza season in Beijing, China.

BACKGROUND: Since 2007, trivalent inactivated influenza vaccine has been provided free-of-charge to older adults aged ≥60 years in Beijing, China, but the data regarding influenza vaccine effectiveness (VE) among these people are very limited so far. We sought to estimate influenza VE against medically-attended laboratory-confirmed influenza illness among older adults during the 2013-2014 season. METHODS: The influenza-like illness (ILI) patients aged 60 years and older who participated in the influenza virological surveillance of Beijing during 2013-2014 influenza season were recruited in this study. A test-negative design was employed to estimate influenza VE among older adults by using logistic regression models. VE was estimated using logistic regression, adjusted for sex, age, interval (days) between illness onset and specimen collection, and week of illness onset. RESULTS: Between 1 November, 2013 and 30 April, 2014, a total of 487 elderly ILI patients were enrolled in the study, including 133 influenza-positive cases (of whom 6.8% were vaccinated) and 354 influenza-negative controls (of whom 10.2% were vaccinated). Among 133 influenza-positive cases, 51 tested positive for A(H1N1)pdm09 virus, 22 positive for A(H3N2) virus, 52 tested positive for B/Yamagata-lineage virus, 2 positive for B/Victoria-lineage virus, 1 positive for both A(H1N1)pdm09 and A(H3N2) viruses, and 5 tested positive for viruses of unknown subtype or lineage. The adjusted overall VE was estimated as 32% (95% CI:-48-69), with 59% (95% CI: -79-90) against A(H1N1)pdm09, 22% (95% CI: -253-83) against A(H3N2) and -20% (95% CI: -239-58) against B/Yamagata-lineage viruses. CONCLUSIONS: These results suggested a modest protective effect of the 2013-2014 influenza vaccine among older adults in Beijing which was not statistically significant, with higher VE against the A(H1N1)pdm09 viruses compared to A(H3N2) and B viruses.

Infectious disease-specific health literacy in Tibet, China.

This study was aimed to develop an instrument to assess infectious disease-specific health literacy (IDSHL) in the general population of Tibet, China and identify the association between IDSHL and reported infectious disease-related symptoms. A survey using a standardized questionnaire, which included 25 questions on knowledge, behaviors and skills regarding infectious diseases, was conducted in the general population of Tibet, China between September 2011 and November 2011. The 25 questions formed the index system of the instrument assessing IDSHL (total scores: 25 scores). Factors associated with index scores of IDSHL were identified by general linear model. The association between the index score of IDSHL and the occurrence of the five selected infectious disease symptoms (fever, diarrhea, rash, jaundice or conjunctivitis) were investigated using multivariate unconditional logistic regression. Among 5717 eligible participants in the survey, 4631 participants completed all of the 25 questions in the instrument. The instrument was reliable and valid as measured by the Cronbach's alpha coefficient and split-half coefficient, and the confirmatory factor analysis. Only 1.0% (48/4631) answered ≥80% of the 25 questions correctly (score ≥ 20). Significant factors associated with lower health literacy score included female gender, older age, Tibetan group, lower education level, underlying diseases and more undeveloped area. For each increasing score of IDSHL, reports of fever, diarrhea or jaundice in the prior year were significantly decreased by 3% (p = 0.015), 4% (p = 0.004) and 16% (p < 0.001), respectively. Accurately measuring IDSHL could help identify those individuals with poor IDSHL, who could be targeted with specific interventions to improve health.

Influenza vaccination in preventing outbreaks in schools: A long-term ecological overview.

Influenza vaccination is the most effective way to reduce the incidence of influenza infections. However, the role of influenza vaccination, such as school-based influenza vaccination, in preventing the influenza outbreaks in schools remains unclear now. In this study, a total of 286 school febrile outbreaks involving 6863 cases in the Beijing area from September 1, 2006 to March 31, 2017 were analyzed. We also tested 294 circulating strains isolated in Beijing during the same period and compared with that of vaccine strains identified every influenza season. The virological match/mismatch between vaccine strains and circulating strains, and the coverage of vaccination in schools were analyzed against outbreaks during the 11 years. It showed that over 80% school febrile outbreaks were caused by influenza A/B virus, the most frequent being A(H3N2) virus (53.25%), followed by A(H1N1)pdm09 virus (25.11%) and B virus (21.64%). More importantly, low vaccine coverage (in 2006-2007 influenza season) and vaccine mismatch (in 2014-2015 and 2015-2016 influenza season) were associated with an increased number of influenza school outbreaks. High vaccination coverage with a matched vaccine can significantly reduce influenza outbreaks in schools (OR: 0.111, p < .001). We have shown the effectiveness of school-based influenza vaccination in preventing outbreaks using trivalent inactivated influenza vaccine in schools. Thus the school-based vaccine policy should be paid more attention in China and other countries worldwide.

H7N9 not only endanger human health but also hit stock marketing.

OBJECTIVE: This study aims to discuss the correlation between daily reported H7N9 cases and stock price indices in China. METHODS: Information on daily reported H7N9 cases and stock market sectors indices between February 19, 2013 and March 31, 2014 were collected. A distributed lag non-linear model was used to describe the variation trend for the stock indices. RESULTS: The daily reported number of H7N9 cases was associated with the closing price of the Avian Influenza Sector Index (P < 0.05) and the opening price of the Shanghai Composite Index (P = 0.029). The Avian Influenza Sector Index decreased with increasing of daily reported case number when daily reported cases ≤ 4. Case number was associated with the opening/closing price of the Chinese Traditional Medicine Sector Index, the Biological Product Sector Index, and the Biomedicine Sector Index (P < 0.05). CONCLUSION: New or reemerging infectious diseases epidemic cause economic loss which is reflected in movements in stock prices.

Influenza vaccine effectiveness against medically attended influenza illness in Beijing, China, 2014/15 season.

Influenza vaccination is the most effective way of preventing influenza infections but its coverage is extremely low in China. Poor influenza vaccine effectiveness (VE) was reported in the 2014/15 season in some Northern Hemisphere countries with a predominance of H3N2 viruses belonging to the 3C.2a clade. However, there is limited information regarding the preventive effect of influenza vaccination for the same season in China, in which H3N2 viruses belonging to the 3C.3a clade predominated. Through influenza virological surveillance in Beijing, China during the 2014/15 season, we estimated the influenza VE against medically attended influenza-like illness (ILI) associated with laboratory-confirmed influenza virus infection using a test-negative design, and the effect of prior vaccination on current vaccination was examined. In total, 9297 patients with ILI were enrolled in this study. Among them, 3434 (36.9%) tested positive for influenza viruses: 2167 (63.1%) for A(H3N2), 1261 (36.7%) for influenza B, and 3 (0.1%) for A(H1N1)pdm09. The adjusted VE was estimated as -25% (95% CI: -70%, 8%) against A(H3N2) and -8% (95% CI: -50%, 23%) against B, with an overall VE of -18% (95% CI: -49%, 6%). The overall VE estimate for patients who received 2014/15 vaccination only was -12% (-57%, 20%), while VE for patients who received both 2013/14 and 2014/15 vaccinations was -27% (-72%, 7%). There was no evidence that the influenza vaccine protected vaccinees against medically attended influenza in Beijing, China during the 2014/15 season.

Influenza Vaccine Effectiveness in Preventing Influenza Illness Among Children During School-based Outbreaks in the 2014-2015 Season in Beijing, China.

BACKGROUND: Little is known about vaccine effectiveness (VE) against nonmedically attended A(H3N2) influenza illness during 2014-2015 when the vaccine component appeared to be a poor match with circulating strains. METHODS: Forty-three eligible school influenza outbreaks in Beijing, China, from November 1, 2014, to December 31, 2014, were included in this study. The VE of 2014-2015 trivalent inactivated influenza vaccine (IIV3) was assessed in preventing laboratory-confirmed influenza among school-age children through a case-control design, using asymptomatic controls. Influenza vaccination was documented from a vaccination registry. VE was estimated adjusting for age group, sex, rural versus urban area, body mass index, chronic conditions, onset week and schools through a mixed effects logistic regression model. RESULTS: The average coverage rate of 2014-2015 IIV3 among students across the 43 schools was 47.6%. The fully adjusted VE of 2014-2015 IIV3 against laboratory-confirmed influenza was 38% [95% confidence interval (CI): 12%-57%]. Receipt of previous season's (2013-2014) IIV3 significantly modified VE of the 2014-2015 IIV3; children who received both 2013-2014 and 2014-2015 vaccinations had VE of 29% (95% CI: -8% to 53%), whereas VE for children who received 2014-2015 IIV3 only was 54% (95% CI: 8%-77%). CONCLUSIONS: VE for 2014-2015 IIV3 against A(H3N2) illness identified in schools was modest. Children who did not receive the prior season's vaccine with a homologous A(H3N2) component may have enjoyed greater protection than repeated vaccinees.

Avian influenza A(H7N9) and (H5N1) infections among poultry and swine workers and the general population in Beijing, China, 2013-2015.

Although several studies have reported seroprevalences of antibody against avian influenza A(H7N9) virus among poultry workers in southern China, results have varied and data in northern China are scarce. To understand risks of H7N9 and H5N1 virus infections in northern China, a serological cohort study was conducted. Poultry workers, swine workers and the general population in Beijing, China, were evaluated through three surveys in November 2013, April 2014 and April 2015. The highest seroprevalence to H7N9 virus among poultry workers was recorded in the April 2014 and April 2015 surveys (0.4%), while that to H5N1 clade 2.3.4 or clade 2.3.2.1 virus was noted in the April 2014 survey (1.6% and 0.2%, respectively). The incidence of H7N9 virus infections among poultry workers (1.6/1000 person-months) was significantly lower than that of H5N1 clade 2.3.4 infections (3.8/1000 person-months) but higher than that of H5N1 clade 2.3.2.1 infections (0.3/1000 person-months). Compared with the general population, poultry workers were at higher risk of contracting H7N9 virus (IRR: 34.90; p < 0.001) or H5N1 clade 2.3.4 virus (IRR: 10.58; p < 0.001). Although risks of H7N9 and H5N1 virus infections remain low in Beijing, continued preventive measures are warranted for poultry workers.

Estimated burden of group a streptococcal pharyngitis among children in Beijing, China.

BACKGROUND: Burden of Group A streptococcus (GAS) pharyngitis is scarce in developing countries, still unknown in China. The objective of this study was to determine the incidence of clinical cases of pharyngitis and GAS culture-positive pharyngitis, and their outpatient visits among children aged 0-14 years in Beijing, the capital of China. METHODS: Multiplier model was used to estimate the numbers of pharyngitis cases, based on reported numbers of clinical cases and GAS culture-positive rates from GAS surveillances in Beijing, consultation rate, population coverage of GAS surveillances, sampling success rate, and test sensitivity of GAS culture from previous studies, surveys and surveillances. RESULTS: An average of 29804.6 (95 % CI: 28333.2-31276.0) clinical cases of pharyngitis per 100,000 person-years occurred among children aged 0-14 years, resulting in correspondingly 19519.0 (95 % CI: 18516.7-20521.2) outpatient visits per 100,000 person-years from 2012 to 2014 in Beijing. On average, there were 2685.1 (95 % CI: 2039.6-3330.6) GAS culture-positive cases of pharyngitis and 1652.7 (95 % CI: 1256.5-2049.0) outpatient visits per 100,000 person-years during the same period. The estimated burden of GAS pharyngitis was significantly higher than that of scarlet fever. Children aged 5-14 years had a higher burden of GAS pharyngitis than those aged 0-4 years. CONCLUSIONS: The present data suggests that GAS pharyngitis is very common in children in China. Further studies and surveillances are needed to monitor trends and the effectiveness of control measures.

Hygiene Behaviors Associated with Influenza-Like Illness among Adults in Beijing, China: A Large, Population-Based Survey.

The objective of this study was to identify possible hygiene behaviors associated with the incidence of ILI among adults in Beijing. In January 2011, we conducted a multi-stage sampling, cross-sectional survey of adults living in Beijing using self-administered anonymous questionnaires. The main outcome variable was self-reported ILI within the past year. Multivariate logistic regression was used to identify factors associated with self-reported ILI. A total of 13003 participants completed the questionnaires. 6068 (46.7%) of all participants reported ILI during the past year. After adjusting for demographic characteristics, the variables significantly associated with a lower likelihood of reporting ILI were regular physical exercise (OR 0.80; 95% CI 0.74-0.87), optimal hand hygiene (OR 0.87; 95% CI 0.80-0.94), face mask use when going to hospitals (OR 0.87; 95% CI 0.80-0.95), and not sharing of towels and handkerchiefs (OR 0.68; 95% CI 0.63-0.73). These results highlight that personal hygiene behaviors were potential preventive factors against the incidence of ILI among adults in Beijing, and future interventions to improve personal hygiene behaviors are needed in Beijing.

Technical guidelines for the application of seasonal influenza vaccine in China (2014-2015).

Influenza, caused by the influenza virus, is a respiratory infectious disease that can severely affect human health. Influenza viruses undergo frequent antigenic changes, thus could spread quickly. Influenza causes seasonal epidemics and outbreaks in public gatherings such as schools, kindergartens, and nursing homes. Certain populations are at risk for severe illness from influenza, including pregnant women, young children, the elderly, and people in any ages with certain chronic diseases.

Cluster of human infections with avian influenza A (H7N9) cases: a temporal and spatial analysis.

OBJECTIVES: This study aims to describe the spatial and temporal characteristics of human infections with H7N9 virus in China using data from February 2013 to March 2014 from the websites of every province's Population and Family Planning Commission. METHODS: A human infection with H7N9 virus dataset was summarized by county to analyze its spatial clustering, and by date of illness onset to analyze its space-time clustering using the ESRI® Geographic Information System (GIS) software ArcMap™ 10.1 and SatScan. RESULTS: Based on active surveillance data, the distribution map of H7N9 cases shows that compared to the rest of China, the areas from near the Yangtze River delta (YRD) to farther south around the Pearl River delta (PRD) had the highest densities of H7N9 cases. The case data shows a strong space-time clustering in the areas on and near the YRD from 26 March to 18 April 2013 and a weak space-time clustering only in the areas on and near the PRD between 3 and 4 February 2014. However, for the rest of the study period, H7N9 cases were spatial-temporally randomly distributed. CONCLUSIONS: Our results suggested that the spatial-temporal clustering of H7N9 in China between 2013 and 2014 is fundamentally different.

The impact of temperature and humidity measures on influenza A (H7N9) outbreaks-evidence from China.

OBJECTIVES: To examine the non-linear effects of meteorological factors on the incidence of influenza A H7N9 and to determine what meteorological measure, and on which day preceding symptom onset, has the most significant effect on H7N9 infection. METHODS: We applied a zero truncated Poisson regression model incorporating smoothed spline functions to assess the non-linear effect of temperature (maximum, minimum, and daily difference) and relative humidity on H7N9 human case numbers occurring in China from February 19, 2013 to February 18, 2014, adjusting for the effects of age and gender. RESULTS: Both daily minimum and daily maximum temperature contributed significantly to human infection with the influenza A H7N9 virus. Models incorporating the non-linear effect of minimum or maximum temperature on day 13 prior to disease onset were found to have the best predictive ability. For minimum temperature, high risk was found to range from approximately 5 to 9°C and moderate risk from -10 to 0°C; temperatures of >9°C represented a low risk. For maximum temperature, high risk was found to range from approximately 13 to 18°C and moderate risk from 0 to 4°C; temperatures of >18°C represented a low risk. Relative humidity was not significantly associated with the incidence of infection. The incidence of H7N9 was higher for males compared to females (p<0.01) and it peaked at around 60-70 years of age. CONCLUSIONS: We provide direct evidence to support the role of climate conditions in the spread of H7N9 and thereby address a critical question fundamental to our understanding of the epidemiology and evolution of H7N9. These findings could be used to inform targeted surveillance and control efforts aimed at reducing the future spread of H7N9.

Influenza vaccine effectiveness against medically-attended influenza illness during the 2012-2013 season in Beijing, China.

BACKGROUND: Influenza vaccine coverage remains low in China, and there is limited information on the preventive value of local vaccination programs. METHODS: As part of influenza virological surveillance in Beijing, China during the 2012-2013 influenza season, we assessed the vaccine effectiveness (VE) of one or more doses of trivalent inactivated influenza vaccine (IIV3) in preventing medically-attended influenza-like-illness (ILI) associated with laboratory-confirmed influenza virus infection using a test-negative case-control design. Influenza vaccination was determined based on self-report by adult patients or the parents of child patients. RESULTS: Of 1998 patients with ILI, 695 (35%) tested positive for influenza viruses, including 292 (42%) A(H3N2), 398 (57%) A(H1N1)pdm09, and 5 (1%) not (sub)typed influenza viruses. The rate of influenza vaccination among all patients was 4% (71/1998). Among influenza positive patients, 2% (57/1303) were vaccinated compared to 4% (14/695) among influenza negative patients, resulting in VE for one or more doses of vaccine (adjusted for age, sex, week, and days since illness onset) against all circulating influenza viruses of 52% (95% CI=12-74%). A significant adjusted VE for one or more doses of vaccine for all ages against A(H1N1)pdm09 of 59% (95% CI, 8-82%) was observed; however, the VE against A(H3N2) was 43% (95% CI, -30% to 75%). The point estimate of VE was 59% (95% CI, 19-79%) for those aged <60 years, but a negative VE point estimate without statistical significance was observed among those aged ≥60 years. CONCLUSIONS: IIV3 conferred moderate protection against medically-attended influenza in Beijing, China during the 2012-2013 season, especially against the A(H1N1)pdm09 strain and among those aged <60 years old.