Symptomatic and Asymptomatic SARS-CoV-2 Infection and Follow-up of Neutralizing Antibody Levels.

Objective: To investigate neutralizing antibody levels in symptomatic and asymptomatic patients with coronavirus disease 2019 (COVID-19) at 6 and 10 months after disease onset. Methods: Blood samples were collected at three different time points from 27 asymptomatic individuals and 69 symptomatic patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Virus-neutralizing antibody titers against SARS-CoV-2 in both groups were measured and statistically analyzed. Results: The symptomatic and asymptomatic groups had higher neutralizing antibodies at 3 months and 1-2 months post polymerase chain reaction confirmation, respectively. However, neutralizing antibodies in both groups dropped significantly to lower levels at 6 months post-PCR confirmation. Conclusion: Continued monitoring of symptomatic and asymptomatic individuals with COVID-19 is key to controlling the infection.

[Survey on seroepidemiological status and vaccine coverage of hepatitis B among children in Chaoyang district of Beijing in 2010].

OBJECTIVE: To explore seroepidemiological status and vaccine coverage of hepatitis B in children aging under 15 years old in Chaoyang district of Beijing. METHODS: A total of 1602 children aging under 15 years old, residents or floating population who had lived here more than six months, were randomly selected by multistage cluster sampling, from Chaoyang district of Beijing in year 2010. The demographic information and vaccine coverage of hepatitis B vaccine (HepB) were collected by self-designed questionnaire.5 ml blood was collected from each subject and the serum HBsAg, anti-HBs and anti-HBc were detected by Abbott microparticle enzyme-linked immunoassay. Those whose HBsAg was positive were then tested HBeAg and anti-HBe. The positive rate of hepatitis B indicators and coverage rate of HepB in different population were compared. RESULTS: The positive rate of HBsAg, anti-HBs and anti-HBc were 0.56% (9/1602), 64.17% (1028/1602) and 2.12% (34/1602), respectively; while the age standardized rates were separately 0.57%, 66.36% and 1.98%; and the gender-adjusted rates were 0.56%, 64.23% and 2.12% respectively. The positive rate of anti-HBs was statistically significant (χ(2) = 165.445, P = 0.000). The positive rate of anti-HBs was up to 90.73% (235/259) among 1-2 years old children, followed by 76.22% (141/185) among 13 - 15 years old children, 67.21% (166/247) among 3 - 4 years old children, 61.22% (150/245) among 9 - 10 years old children, 60.68% (142/234) among 11 - 12 years old children, 49.05% (103/210) among 5 - 6 years old children and 40.99% (91/222) among 7 - 8 years old children. The average coverage rate of HepB was 90.44% (1371/1516), separately 93.76% (661/705) in residents and 87.55% (719/811) in floating population. The difference was statistically significant (χ(2) = 16.829, P = 0.000). CONCLUSION: HBsAg positive rate in children under 15 years old in Chaoyang district of Beijing dropped to less than 1% and the coverage rate of HepB had reached over 90%. It is suggested that we should pay more attention to increase the coverage rate of HepB among floating children under 15 years old.

[Investigation on measles cases of new genotype D8 in Beijing, 2013].

OBJECTIVE: To investigate the epidemiological characteristics of measles cases of new genotype D8 in Beijing from January to June, 2013. METHODS: Epidemiological survey and descriptive analysis was conducted. RESULTS: 661 suspected measles were reported from January to June, 2013. 416 were confirmed measles cases by serology and etiology detection. 28 measles cases were caused by genotype D8 measles virus by genotype identification. There were 2 measles outbreak including 14 cases and 14 sporadic cases. The incidence peak was during April and May. 25 cases (89.3%, 25/28) occurred in downtown and suburban districts. 22 cases (78.5%, 22/28) were adults aged 15-39 years and 19 cases (67.9%, 19/28) were migrant population. 12 cases (85.7%, 12/14) in outbreak were migrant population working in clothing sales. There was epidemiological association between 2 outbreaks. CONCLUSION: Measles cases of genotype D8 were found for the first time in Beijing. Genotype D8 virus mainly infected migrant adults and caused local outbreak and endemic.

[Analysis of measles immunity level in persistent populations in Beijing, 2012].

OBJECTIVE: To analyze the measles immunity level of persistent population in Beijing. METHODS: A total of 2125 objects from 10 age groups, who had been living in Beijing for over 6 months, were selected from urban and rural areas in Beijing in 2012. Demographic characteristics, history of measles and vaccine immunization were investigated by questionnaire. 5 ml blood sample of each subject was collected, and the Measles IgG antibody was measured by ELISA assay. RESULTS: Positive rate of measles antibody was 84.71% (1800/2125) and standardized positive rate was 88.07% . Median of antibody was 960.46 IU/L. Positive rate and median of measles antibody were significantly different between population from different age groups (χ(2) = 341.60, P < 0.01; H = 216.27, P < 0.01). Antibody positive rate and median were lowest in the <1 year age group, which were separately 43.06% (90/209) and 185.80 IU/L; and highest in the 1-4 (97.31% (181/186) and 2448.81 IU/L) and 5-9 years age group (96.46% (218/226) and 1910.72 IU/L). The range of antibody positive rate and median in adults of ≥ 15 years were 81.98%-90.14% and 744.38-1474.84 IU/L. Antibody positive rate and median in persistent population, which were separately 82.45% (883/1071) and 899.82 IU/L, were lower than those in migrant population, which were 87.00% (917/1054) and 166.19 IU/L, respectively (χ(2) = 8.51, P < 0.01;U = 538 704.00, P < 0.01). Antibody positive rate and median in population with vaccination history, which were separately 91.95% (891/969) and 1443.11 IU/L, were higher than those population without vaccination history and people whose history unknown (32.95% (57/173) , 127.33 IU/L; 86.67% (852/983) , 923.73 IU/L). The difference showed statistical significance (χ(2) = 399.92, P < 0.01; H = 202.11, P < 0.01). CONCLUSION: Among the persistent population in China, measles antibody level among the children aging 1-9 years old was high enough to prevent outbreak and epidemic of measles. However, we should try our best to strengthen the measles antibody level among the babies younger than 1 year old and the migrant population aging between 15 and 40 years old.

[Study on family aggregation and risk factors of hepatitis B virus transmission in Chaoyang district, Beijing].

OBJECTIVE: To explore the family aggregation and risk factors of hepatitis B virus (HBV) transmission in Chaoyang district of Beijing. METHODS: A total of 5266 families were randomly selected for the multi-stage cluster sampling study in Chaoyang district of Beijing in 2010. The family members who aged between 1 and 70 years old and lived constantly in Beijing for over half a year, were recruited as subjects. There were 14 491 subjects in total, including temporary residents who did not have Beijing household account, except foreigners. 5 ml venous blood was drawn from every subject. A self-designed questionnaire was used to collect the basic information of the population and the risk factors of the hepatitis B transmission. Microparticle enzyme-linked immunoassay was applied to test five indicators of hepatitis B. Negative binomial distribution test was used among the HBsAg positive families to calculate the family aggregation rate of hepatitis B. Single factor analysis and multi-factor logistic regression model were used to analyze the risk factors of HBV transmission. RESULTS: In all, 308 out of 5266 families had HBsAg positive members, accounting for 5.85%.383 out of 14 410 subjects were HBsAg positive, rating at 2.66%. The HBsAg positive rate among subjects under 14 years old was the lowest, at 0.56% (9/1603); and the positive rate among subjects aging between 35 and 44 years old was the highest, at 4.27% (47/1029). Negative binomial distribution test showed that the family aggregation rate of HBV infection was 7.66% (χ² = 15.10, P < 0.05). The analysis of family aggregation of HBsAg positive showed that 17.39% (8/46) of the transmission was from father to child, 13.04% (6/46) was from mother to child, 30.44% (14/46) was between couples, and another 39.13% (18/46) was between siblings or other relatives. Both single factor analysis and multi-factor logistic regression analysis showed that hepatitis B positive family members (OR = 5.40, 95%CI: 5.24 - 5.55), hepatitis B positive friends and colleagues (OR = 1.55, 95%CI: 1.11 - 1.99) and blood donation and transfusion history (OR = 1.96, 95%CI: 1.76 - 2.15) were the risk factors of HBV infection. CONCLUSION: HBV transmission showed family aggregation in Beijing, however, the risk factors needed further studies.

[Study of immunogenicity after primary vaccination by different sequential program of inactivated poliovirus vaccine and oral poliovirus vaccine].

OBJECTIVE: To evaluate immunogenicity after primary vaccination by different sequential program of inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV). METHODS: Children of 2 months old (60-89 days) selected in Beijing were assigned to 4 groups, 1 dose IPV plus 2 doses OPV (I-O-O, 122 children), 2 doses IPV plus 1 dose OPV(I-I-O, 103 children), 3 doses IPV (I-I-I, 114 children), and 3 doses OPV (O-O-O, 106 children), and were vaccinated at the age of 2, 3, 4 months. Polio neutralizing antibody titers against poliovirus types 1, 2, and 3 were tested and protective rates were calculated before the 1st dose, after the last dose, and after the 1st and 2nd dose of IPV. RESULTS: After the primary immunization, geometric mean titers (GMT) of polio neutralizing antibody titers against poliovirus types 1, 2, and 3 were 788.32, 738.42 and 631.17 in O-O-O group, 212.02, 262.30 and 537.52 in I-I-I group, 940.35, 929.72 and 940.35 in I-O-O group and 901.09, 1102.68 and 1110.12 in I-I-O group (F values were 47.71, 53.84, and 9.81 respectively, all P values<0.01). The protective rate of three types among each group was 98.1% (104/106)-100.0% and the difference was not statistically significant (P>0.05). After the 1(st) dose of IPV, the GMT were 18.88, 37.77, 24.64 and the protective rate was 82.6% (122/138)-96.4% (133/138); after the 2nd dose of IPV, GMT were 177.03, 168.25, 321.86 and the protective rate was 99.1% (108/109)-100.0% (109/109) in antibody types 1, 2 and 3, respectively. CONCLUSION: GMT of polio neutralizing antibody titers against poliovirus is higher after vaccination by sequential program of IPV and OPV than that by IPV or OPV 3-doses program. High level of protective rate after 2 doses of IPV in I-I-O group may lead to better protection from vaccine associated paralytic poliomyelitis (VAPP). Sequential program of IPV and OPV can be used to maintain high level of herd immunity and to prevent VAPP, and the I-I-O sequential program should be the first choice.

[Prevalence of hepatitis B in Chaoyang district, Beijing in 2010].

OBJECTIVE: To study the prevalence of hepatitis B infections and carrier status among general population in Chaoyang district, Beijing in 2010. METHODS: From May to December 2010, 14 491 subjects over 12 months old were selected by multistage random cluster sampling method from residents in Chaoyang district, Beijing. Five millilitre venous blood specimens were collected from these subjects to test hepatitis B virus antigens and antibodies. Status of hepatitis B infections were analyzed in different age, sex and registered permanent residence groups. RESULTS: The overall positive rate of surface antigen (HBsAg) was 2.66% (383/14 410). The lowest rate of 0.56% (9/1603) was found in the 1 to 14 years old group and the 35 to 44 years old group had the highest rate of 4.27% (92/2154). The rate in subjects younger than 24 years old was 1.03% (31/2986). The overall positive rate of surface antibody (anti-HBs) was 40.21% (5798/14 421). The highest positive rate of anti-HBs (80.59%, 407/505) was found in the 1 to 4 years old group. The overall positive rate of core antibody (anti-HBc) was 30.26% (4364/14 424). The overall hepatitis B virus infection rate was 30.32% (4364/14 393). For male and female groups, the positive rates of HBsAg were 2.93% (179/6108) and 2.44% (202/8287) respectively (χ² = 3.32, P > 0.05); anti-HBs were 41.93% (2563/6113) and 38.96% (3231/8293) respectively (χ² = 12.88, P < 0.01); and anti-HBc were 31.39% (1919/6114) and 29.39% (2438/8295) respectively (χ² = 6.65, P = 0.01). For local residents group and mobile population group, the positive rates of HBsAg were 2.46% (283/11 510) and 3.60% (98/2719) respectively (χ² = 11.08, P < 0.01); anti-HBs were 37.11% (4293/11 568) and 53.07% (1445/2723) respectively (χ² = 233.51, P < 0.01); and anti-HBc were 30.83% (3567/11 570), and 28.41% (774/2724) respectively (χ² = 6.08, P < 0.05). CONCLUSION: The positive rate of HBsAg in population younger than 24 years old has reached a relatively low level. The mobile population has significantly higher positive rate of HBsAg than local residents, indicating the need for enhancing prevention and control measures for hepatitis B for the mobile population and local residents over 25 years old.

[The epidemiological impact of varicella vaccination in kindergartens, primary and secondary schools in Beijing].

OBJECTIVE: To study the epidemiological impact of varicella vaccine vaccination on kindergartens and school children in Beijing. METHODS: According to "China Information System for Diseases Control and Prevention", the reported clinical diagnosis varicella cases were tracked in kindergartens, primary and secondary schools whose onset date were from 2008 to 2010. Epidemiological survey was conducted and epidemiological features were analyzed. RESULTS: A total of 21 474 varicella cases were investigated: 55.3% (11 883 cases) had been vaccinated by varicella vaccine. Of cases with definite immunization history, interval between vaccination date and onset date were from 30 days to 1 year accounted for 3.4% (286/8510), 1 to 3 years accounted for 18.2% (1551/8510), 3 to 5 years accounted for 28.6% (2431/8510), 5 to 10 years accounted for 34.3% (2916/8510) (left-closed right-open interval); The peak age of onset was 4 years old in cases without immunization history, which was 6 years old in cases with immunization history; The proportion of cases with immunization history (≥ 30 days) had increased from 42.4% (2862/6754) in 2008 to 56.3% (4327/7679) in 2010. The cases with no fever had a higher proportion (54.9%, 6413/11 679) of immunization history (≥ 30 days) than cases with fever (47.7%, 4533/9500) (P < 0.01); The cases with rashes less than 50 had a higher proportion (57.4%, 8045/14 020) of immunization history (≥ 30 days) than cases with rashes more than 50 (40.2%, 2902/7216) (P < 0.01). CONCLUSION: Varicella vaccine delays the peak age of onset, alleviates the symptoms. The current immunization strategy can not block varicella spread in kindergartens, primary and secondary schools.

[A case-control study of the transmission of pandemic influenza A (H1N1) virus in families].

OBJECTIVE: To explore the characteristics of transmission of pandemic influenza A/H1N1, and to analyze the possible factors of influencing transmission in families and to provide scientific evidence for formulating strategies of H1N1 prevention and control. METHODS: A 1:2 matched case-control study was conducted. The case was defined as a household with 2 or more cases and the control was defined as that with 1 case. Face-to-face interview with questionnaire was used to collect information of work and family life of the study participants. Conditional logistic regression was used to analyze the data. RESULTS: Univariate analysis showed that factors such as education level of the secondary case, the number of family members, per capita living space, flu-like symptom, insulation of case, ventilation, hand-washing, and influenza A/H1N1 vaccine immunization were all associated with infection of influenza A/H1N1. Results of multivariate logistic regression analysis showed that variables such as education level of secondary case (OR = 0.42), insulation of case (OR = 3.29), ventilation, (OR = 0.28), hand-washing (OR = 0.71), influenza A/H1N1 vaccine immunization (OR = 0.05) were all correlated to infection of influenza A/H1N1. CONCLUSIONS: Factors such as vaccine, insulation, ventilation, and hand-washing can help persons in protection from infection of influenza A/H1N1, suggesting the importance of good hygienic habit and immunization with influenza A/H1N1 vaccine.

[Epidemiological characteristics of infection for close contacts of pandemic (H1N1) 2009 in Beijing].

OBJECTIVE: To examine the epidemiological characteristics of infection for close contacts of pandemic (H1N1) 2009 and to provide scientific evidence for preparedness and response for the next pandemic. METHODS: A total of 613 index cases with clear information of close contacts and their 7099 close contacts, determined between May 16 and September 15, 2009, were included in this study. Based on data of epidemiological investigation, sampling and test of index cases and close contacts, the characteristics of infection for close contacts were described. RESULTS: 56.8% (348/613) of the index cases were male, and 43.2% (265/613) were female, and the median age was 20 years (range: 1 - 75 years). 49.6% (3518/7099) of the close contacts were male, and 49.5% (3514/7099) were female, but the sex information of 0.9% (67/7099) could not be recorded. The median age of the close contacts was 27 years (range: 0 - 99 years). 2.4% (167/7099) of close contacts were infected. The attack rates decreased with increasing age of close contacts (χ()2 = 27.87, P < 0.001), and were significantly different between various contact patterns of close contacts (χ()2 = 109.76, P < 0.001). 14.4% of the infected close contacts were asymptomatic. For close contacts with symptomatic infection, virus could be shed 4.5 days before illness onset, and the median generation time was 2.4 days. CONCLUSION: The attack rate of close contacts was very low; and the attack rates were different between various ages and contact patterns of close contacts. In this series 14% of cases with pandemic (H1N1) 2009 were asymptomatic. The symptomatic cases might have infectivity 1 day earlier before illness onset.

Serologic survey of pandemic influenza A (H1N1 2009) in Beijing, China.

OBJECTIVE: To examine the frequency and distribution of antibodies against pandemic influenza A (H1N1 2009) [H1N1] in populations in Beijing and elucidate influencing factors. METHODS: In January 2010, a randomized serologic survey of pandemic influenza A (H1N1 2009) was carried out. Six districts that were randomly selected with a total of 4601 participants involved in the survey have their antibody level tested by hemagglutination inhibition assay. RESULTS: Among the 4601 participants, the overall seropositive rate for pandemic influenza A (H1N1 2009) antibodies was 31.7%. The seropositivity prevalence in participants who received the pandemic H1N1 vaccination was 60.9%. Only 53.1% of the pandemic influenza A (H1N1 2009) seropositive individuals who had not received the vaccination experienced respiratory tract infection symptoms. Multivariate logistic regression revealed that factors such as age, occupation, dwelling type, whether the participant's family included students in school, and the vaccination history with pandemic influenza A (H1N1 2009) were associated with antibody titers (p<0.05). CONCLUSIONS: Our data indicated that almost 30.0% of the residents had appropriate antibody titers against pandemic influenza A (H1N1 2009) in Beijing, and these titers may provide an immune barrier.

[Analysis of adverse events following 2009 influenza A (H1N1) vaccinoprophylaxis in Beijing].

OBJECTIVE: To evaluate the safety of 2009 influenza A (H1N1) vaccine based on mass immunization initiative in Beijing. METHOD: There were 2 113 280 people were vaccinated during September to December 2009. The information of adverse events following immunization (AEFI) was collected through surveillance system, and descriptive methodology was used for data analysis. RESULTS: A Total of 612 AEFI cases were reported, among which there were 321 vaccine reaction cases following immunization, 203 coincidental illness cases, 82 psychogenic reaction cases, and 6 pending cases. The rates of rare reactions and common reactions associated with vaccination were respectively 5.54/100 000 (117/2 113 280) and 9.65/100 000 (204/2 113 280). The rate of serious rare reaction was 0.19/100 000 (4/2 113 280). The rates of vaccine reactions in urban, suburb and county were 16.87/100 000 (36/213 519), 17.81/100 000 (187/1 049 817) and 11.53/100 000 (98/849 944), respectively. The rates of rare reaction and common reaction in different age groups were between 3.65/100 000 (6/164 604) to 8.99/100 000 (27/300 176), and between 0.61/100 000 (1/164 604) to 22.06/100 000 (85/385 275). The 117 rear vaccine reaction cases were mainly allergic reaction (107 cases), and the 204 common vaccine reaction cases were mainly fever (176 cases). There were 91.90% (295/321) vaccine reactions occurred within 24 hours of administration, and all cases had improved consequence. CONCLUSION: The mostly symptoms of AEFI cases during the period of 2009 influenza A (H1N1) vaccinoprophylaxis were anaphylaxis and fever. The types of adverse reactions and the level of serious events are consistent with the anticipation. There were no rear or new events occurred.

[Study on the cellular and humoral immunity effect of recombinant Chinese hamster ovary cell hepatitis B vaccine in adults].

OBJECTIVE: To evaluate the cellular and humoral immunity effect of 10 µg and 20 µg recombinant Chinese hamster ovary (CHO) cell hepatitis B vaccine in adults by randomized double-blind controlled trials. METHOD: A total of 642 adults aged 18 - 45 years old, non-vaccinated against hepatitis B, and hepatitis B five blood indicators negative were selected as the study subjects. The study subjects were randomly divided into two groups and each group had 321 subjects. The subjects were given 10 µg and 20 µg recombinant CHO hepatitis B vaccination respectively by 0, 1st, 6th month schedule. Blood sample was collected from each study subject one month after the second dose vaccination. The anti-HBs level was detected by Abbott chemiluminescence detection method (I2000) to evaluate humoral immunity status. Of all the study objects, 153 cases were randomly selected by the Excel random function. Their blood samples were collected and Lymphocyte were separated to detect the IL-4 and IFN-γ levels in vitro by enzyme-linked immunospot (ELISPOT) method to evaluate the cellular immunity status. RESULTS: The anti-HBs seroconversion rates in 10 µg and 20 µg dose group were 88.8% (285/321) and 95.3% (306/321) respectively, and 95%CI were 85.4% - 92.2% and 93.0% - 97.6% respectively. The spot forming cell (SFC) of IL-4 of the 20 µg-dose group (x(-) = 20.31) were significantly higher than the 10 µg-dose group (x(-) = 8.19, t = 3.27, P < 0.01). With the increasing of anti-HBs titer, the SFC of IL-4 also went up significantly. There was a positive correlation between SFC of IL-4 and anti-HBs (Spearman correlation coefficient = 0.538, P < 0.0001). No significant difference was found for IFN-γ SFC in two groups (10 µg group: x(-) = 1.49; 20 µg group: x(-) = 0.86; t = 1.83, P > 0.05). CONCLUSION: The humoral and cellular immune effects of 20 µg recombinant CHO hepatitis B vaccine are better than that of the 10 µg recombinant CHO hepatitis B vaccine.20 µg recombinant CHO hepatitis B vaccine should be chosen as the adult's hepatitis B prevention vaccine.

[Study on the immuno-effects and influencing factors of Chinese hamster ovary (CHO) cell hepatitis B vaccine among adults, under different dosages].

OBJECTIVE: To evaluate the immuno-effect and related influencing factors on 10 µg and 20 µg Chinese hamster ovary (CHO) cell hepatitis B vaccine, using the randomized double-blind controlled trials in adult population. METHODS: A total of 642 adults aged 18 - 45 years old, non-vaccinated against hepatitis B, and negative on five blood indicators for hepatitis B, were selected as the study objects from four districts in Beijing. The study objects were randomly divided into two groups, and then accepted 10 µg and 20 µg recombinant CHO hepatitis B vaccination by 0 - 1 - 6 month schedule. Influencing factors were investigated by means of questionnaire. Blood samples were collected one month after the third dose of vaccination. Anti-HBs level was detected by Abott chemiluminescence detection method. For the anti-HBs negative person, fluorescent quantitative PCR method was used to find out if the person had been infected with HBV. Logistic regression analysis was used to find out the influencing factors of anti-HBs seroconversion on every studied subject. RESULTS: The anti-HBs seroconversion rates on 10 µg and 20 µg dose groups were 88.8% (95%CI: 85.4% - 92.2%) and 95.3% (95%CI: 93.0% - 97.6%) respectively. Taking the anti-HBs level < 100 mIU/ml as the low/non-response standard, the low response and non-response rates were 34.3% and 17.4% respectively. The geometric mean titers (GMT) of anti-HBs were 173.42 mIU/ml for the 10 µg dose group and 588.51 mIU/ml for the 20 µg dose group. Data from the Multivariate analysis showed that:diabetes, spouses infected with hepatitis B virus and old age were unfavorable factors for anti-HBs Seroconversion. 20 µg dose of the vaccine was conducive to seroconversion. CONCLUSION: 20 µg CHO hepatitis B vaccine seemed better than 10 µg CHO hepatitis B vaccine while many factors need to be taken into account for evaluation on hepatitis B vaccines.

[A survey on serological epidemiology of influenza A (H1N1) 2009 in Beijing].

OBJECTIVE: To investigate the immunological level against influenza A (H1N1) 2009 in Beijing and provide evidence to evaluate the developing trend of the disease. METHODS: Between Nov. 27, 2009 and Dec. 23, 2009, subjects were randomly selected from patients in hospitals (infectious and respiratory diseases related departments were excluded), volunteers in blood donation center and healthy subjects attending the physical examination center. Questionnaire survey was conducted and serum samples were collected to detect the hemagglutination-inhibition (HI) antibody against influenza A (H1N1) 2009 virus. RESULTS: 856 subjects participated in this survey, and 127 showed positive HI antibody to this pandemic virus. The proportions of sero-positivity among 0 - 5, 6 - 17, 18 - 55, ≥ 56 year olds were 14.5%, 19.4%, 17.4% and 8.0% respectively (P = 0.009). There was no significant difference in the sero-positivity between males and females (P = 0.693). The age-adjusted positive rate was 15.8% in the population of Beijing. By multivariate logistic regression analysis, factors as age, acute respiratory symptoms and the rate of pandemic (H1N1) 2009 vaccination were significantly associated with sero-positivity of HI antibody to the influenza A (H1N1) 2009 virus. CONCLUSION: Above 15% of the population in Beijing showed protective antibody against influenza A (H1N1) 2009 virus, indicating the development of immunological barrier to this disease had been formed, to some extent.

[Etiological characteristics of influenza A (H1N1) 2009 virus in Beijing].

OBJECTIVE: To analyze the results of detection on influenza A (H1N1) 2009 virus in Beijing from May 2009 to December 2009 and to understand the epidemiologic characteristics during the pandemic period. METHODS: The study was conducted from the May 1 to December 27, 2009. A total of 101 852 throat swab samples were detected with the real-time RT-PCR assay by the Beijing Network Laboratory. Data was statistically analyzed. RESULTS: 9843 samples showed influenza A (H1N1) 2009 positive, with an overall positive rate as 9.66%. In terms of the positive rates, they were 2.85% from May to June, 3.32% from July to August and 8.35% from September to October. The peak month fell in November (29.67%) and December (24.33%). The positive rates among the following subpopulations were: 8.40% among the suspected cases, 4.75% among close contact cases, 11.46% among the influenza-like illness cases and 7.33% among the cluster cases with fever. Positive cases mainly fell in age groups 5 - 14 and 15 - 24. The ratio of male to female was 1.5:1. CONCLUSION: During the pandemic period of influenza A (H1N1) 2009, positive cases gradually increased during May to November but slowly decreasing in December.

[Estimation on the real number of novel influenza A (H1N1) cases, Beijing, 2009].

OBJECTIVE: To estimate the real number of novel influenza A (H1N1) infection in Beijing, 2009. METHODS: A multiplier model (Impact 2009 v 1.0 software) based on Monte Carlo approach was used to estimate the real number of novel influenza A (H1N1) based on the number of influenza-like illness (ILI) cases, novel influenza A (H1N1) positive rate among ILI cases and rate on clinical visit of ILIs in secondary and tertiary hospitals. RESULTS: There were 1.80 million (90%CI: 1.46 - 2.30) estimated novel influenza A (H1N1) cases in 2009 in Beijing with the rate of infection as 11.0%. One reported case would represent 167 real infections. The highest age groups of infection were 0 - 4 years and 5 - 14 years, being 32.5% and 33.3%, respectively. CONCLUSION: Laboratory-confirmed infections with novel influenza A (H1N1) only represented a fraction of the total cases in a population, suggesting that it was imperative to estimate the real number of novel influenza A (H1N1) infection.

[Herd immunity against new influenza A (H1N1) in pre-vaccinated residents aged over 5 years in Beijing].

OBJECTIVE: To explore the herd immunity against influenza A (H1N1) in pre-vaccinated residents aged over 5 years, and therefore to provide data for vaccination policies in high risk populations. METHODS: From October to December 2009, Beijing CDC conducted a serum survey of the novel influenza A (H1N1) in the local residents, stratified in 10 age groups between 5 years to over 60 years, without H1N1 vaccination history and disease history. Hemagglutination inhibition (HI) assays were performed at Beijing CDC. Statistical significance was determined with geometric mean titer (GMT). RESULTS: 3499 serum samples were tested for HI antibody. The average level of HI antibody was 1:8.03, and 11.06% (387/3499) were sero-positive (HI antibody level ≥ 1:40). In the group aged from 5 to 19 years, the level of HI antibody and the sero-positive rate were higher (HI antibody > 1:8.9, sero-positive rate > 12%). CONCLUSIONS: The antibody levels in different groups were affected by age specific morbidity, and the higher antibody level of the school-age group was correlated with higher disease intensity in this population. The data showed that the herd immunity in Beijing was under the optimal level, but influenza A (H1N1) would probably become prevalent in the short coming future.