Debates persist regarding the efficacy and safety of azvudine, particularly its real-world outcomes. This study involved patients aged ≥60 years who were admitted to 25 hospitals in mainland China with confirmed SARS-CoV-2 infection between December 1, 2022, and February 28, 2023. Efficacy outcomes were all-cause mortality during hospitalization, the proportion of patients discharged with recovery, time to nucleic acid-negative conversion (T _NANC), time to symptom improvement (T _SI), and time of hospital stay (T _HS). Safety was also assessed. Among the 5884 participants identified, 1999 received azvudine, and 1999 matched controls were included after exclusion and propensity score matching. Azvudine recipients exhibited lower all-cause mortality compared with controls in the overall population (13.3% vs. 17.1%, RR, 0.78; 95% CI, 0.67-0.90; P = 0.001) and in the severe subgroup (25.7% vs. 33.7%; RR, 0.76; 95% CI, 0.66-0.88; P < 0.001). A higher proportion of patients discharged with recovery, and a shorter T _NANC were associated with azvudine recipients, especially in the severe subgroup. The incidence of adverse events in azvudine recipients was comparable to that in the control group (2.3% vs. 1.7%, P = 0.170). In conclusion, azvudine showed efficacy and safety in older patients hospitalized with COVID-19 during the SARS-CoV-2 omicron wave in China.

OBJECTIVE: To investigate the mechanism of human embryonic stem cell-derived mesenchymal stem cells (hESC-MSC) in alleviating brain injury after resuscitation in swine with cardiac arrest (CA). METHODS: Twenty-nine healthy male large white swine were randomly divided into Sham group (n = 9), cardiopulmonary resuscitation (CPR) group (n = 10) and hESC-MSC group (n = 10). The Sham group only completed animal preparation. In CPR group and hESC-MSC group, the swine model of CA-CPR was established by inducing ventricular fibrillation for 10 minutes with electrical stimulation and CPR for 6 minutes. At 5 minutes after successful resuscitation, hESC-MSC 2.5×10⁶/kg was injected via intravenous micropump within 1 hour in hESC-MSC group. Venous blood samples were collected before resuscitation and at 4, 8, 24, 48 and 72 hours of resuscitation. The levels of neuron specific enolase (NSE) and S100B protein (S100B) were detected by enzyme linked immunosorbent assay (ELISA). At 24, 48 and 72 hours of resuscitation, neurological deficit score (NDS) and cerebral performance category (CPC) were used to evaluate the neurological function of the animals. Three animals from each group were randomly selected and euthanized at 24, 48, and 72 hours of resuscitation, and the hippocampus tissues were quickly obtained. Immunofluorescence staining was used to detect the distribution of hESC-MSC in hippocampus. Immunohistochemical staining was used to detect the activation of astrocytes and microglia and the survival of neurons in the hippocampus. The degree of apoptosis was detected by TdT-mediated dUTP nick end labeling (TUNEL). RESULTS: The serum NSE and S100B levels of brain injury markers in CPR group and hESC-MSC group were significantly higher than those in Sham group at 24 hours of resuscitation, and then gradually increased. The levels of NSE and S100B in serum at each time of resuscitation in hESC-MSC group were significantly lower than those in CPR group [NSE (μg/L): 20.69±3.62 vs. 28.95±3.48 at 4 hours, 27.04±5.56 vs. 48.59±9.22 at 72 hours; S100B (μg/L): 2.29±0.39 vs. 3.60±0.73 at 4 hours, 2.38±0.15 vs. 3.92±0.50 at 72 hours, all P < 0.05]. In terms of neurological function, compared with the Sham group, the NDS score and CPC score in the CPR group and hESC-MSC group increased significantly at 24 hours of resuscitation, and then gradually decreased. The NDS and CPC scores of hESC-MSC group were significantly lower than those of CPR group at 24 hours of resuscitation (NDS: 111.67±20.21 vs. 170.00±21.79, CPC: 2.33±0.29 vs. 3.00±0.00, both P < 0.05). The expression of hESC-MSC positive markers CD73, CD90 and CD105 in the hippocampus of hESC-MSC group at 24, 48 and 72 hours of resuscitation was observed under fluorescence microscope, indicating that hESC-MSC could homing to the damaged hippocampus. In addition, compared with Sham group, the proportion of astrocytes, microglia and apoptotic index in hippocampus of CPR group were significantly increased, and the proportion of neurons was significantly decreased at 24, 48 and 72 hours of resuscitation. Compared with CPR group, the proportion of astrocytes, microglia and apoptotic index in hippocampus of hESC-MSC group decreased and the proportion of neurons increased significantly at 24 hours of resuscitation [proportion of astrocytes: (14.33±1.00)% vs. (30.78±2.69)%, proportion of microglia: (12.00±0.88)% vs. (27.89±5.68)%, apoptotic index: (12.89±3.86)% vs. (52.33±7.77)%, proportion of neurons: (39.44±3.72)% vs. (28.33±1.53)%, all P < 0.05]. CONCLUSIONS Application of hESC-MSC at the early stage of resuscitation can reduce the brain injury and neurological dysfunction after resuscitation in swine with CA. The mechanism may be related to the inhibition of immune cell activation, reduction of cell apoptosis and promotion of neuronal survival.
Animals ; Heart Arrest/therapy* ; Cardiopulmonary Resuscitation ; Swine ; Humans ; Male ; Human Embryonic Stem Cells/cytology* ; Mesenchymal Stem Cell Transplantation ; Mesenchymal Stem Cells/cytology* ; Phosphopyruvate Hydratase/blood* ; Brain Injuries/therapy* ; S100 Calcium Binding Protein beta Subunit ; Apoptosis ; Disease Models, Animal

Objective:To explore the protective efficacy of sulforaphane (SFN) in alleviating intestinal mucosal injury after resuscitation in pigs and its possible mechanism.Methods:This experiment was performed in the laboratory animal center, Zhejiang university. Using a random number table, twenty-four domestic healthy male white pigs were randomly divided into the Sham group, cardiopulmonary resuscitation (CPR) group, and SFN group, in which the Sham group had 6 pigs, and the other two groups had 9 pigs, respectively. The experimental parameters of 10 min of cardiac arrest and 6 min of CPR were chosen to establish the porcine model of CPR in the CPR and SFN groups. At 5 min after resuscitation, a dose of 2 mg/kg of SFN was infused via the femoral vein within 10 min in the SFN group. At 1 h, 2 h, 4 h, and 24 h after resuscitation, vein samples were collected, and then the levels of intestinal fatty acid binding protein (IFABP) and diamine oxidase (DAO) in serum were measured by ELISA. Subsequently, 6 pigs were chosen to be euthanized in each group, and then tissue samples were harvested from distal ileum to measure the level of cell apoptosis by TUNEL, the activities of superoxide dismutase (SOD) and catalase (CAT) and the contents of glutathione (GSH) and malondialdehyde (MDA) by biochemical method, the contents of 4-hydroxy-2-nonenal (4-HNE) by ELISA, the fluorescence intensity of reactive oxygen species (ROS) by immunofluorescence staining, and the expression levels of zonula occluden-1 (ZO-1), occludin, nuclear factor E2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) by Western blot. Continuous variables were compared with one way analysis of variance among the three groups, and Bonferroni test was used for further pairwise comparison.Results:During the observation period after resuscitation, the serum levels of biomarkers of intestinal mucosal injury including IFABP and DAO were significantly higher in the CPR and SFN groups than in the Sham group (all P<0.05). However, the serum levels of IFABP at 2 h, 4 h, and 24 h after resuscitation and the serum levels of DAO at 1 h, 2 h, 4 h, and 24 h after resuscitation were significantly lower in the SFN group than in the CPR group (all P<0.05). At 24 h after resuscitation, apoptotic index was significantly increased, SOD and CAT activities and GSH contents were significantly decreased, MDA and 4-HNE contents and ROS production were significantly increased, ZO-1 and occludin expression were significantly down-regulated, and Nrf2 and HO-1 expression were significantly up-regulated in the CPR and SFN groups when compared with the Sham group (all P<0.05). However, apoptotic index was significantly decreased, SOD and CAT activities and GSH contents were significantly increased, MDA and 4-HNE contents and ROS production were significantly decreased, and ZO-1, occludin, Nrf2, and HO-1 expression were significantly up-regulated in the SFN group when compared to the CPR group (all P<0.05). Conclusion:SFN could effectively protect against intestinal mucosal injury after resuscitation in pigs, and its mechanism was possibly related to the inhibition of oxidative stress and cell apoptosis via the activation of Nrf2/HO-1 pathway.

Objective:To establish pig cardiac arrest resuscitation model, and explore the effect of automatic compression synchronous ventilation (ACSV) on cardiopulmonary resuscitation in pigs.Methods:Twelve male white pigs with body weight of (38±3) kg were divided into ACSV group and intermittent positive pressure ventilation (IPPV) group with 6 pigs in each group by random number table method. A porcine cardiac arrest and resuscitation model was prepared with ventricular fibrillation induced by alternating current release via right ventricular electrode for 6 min and compression for 8 min. Mechanical chest external compression depth 5 cm, frequency 100 times/min. The tidal volume of ACSV group was 3 mL/kg and the frequency was 100 times/min. In the IPPV group, the tidal volume was 7 mL/kg and the frequency was 10 times/min. Arterial blood was drawn before resuscitation and at 1, 4 and 7min during resuscitation for blood gas analysis. Coronary perfusion pressure (CPP), end-respiratory carbon dioxide (ETCO 2) and carotid blood flow (CBF) were monitored during resuscitation. Stroke volume (SV) and global ejection fraction (GEF) were recorded by pressure monitoring catheter before and 1, 2 and 4 h after resuscitation. Venous blood samples were collected at each time point and 24 h after resuscitation to detect cardiac troponin I (cTnI), neuron specific enolase (NSE), alamine aminotransferase (ALT), creatinine (Cr), and intestinal fatty acid binding protein (IFABP). Results:(1) During resuscitation, CPP, ETCO 2 and CBF in ACSV group were slightly higher than those in IPPV group, but the differences between groups were not statistically significant. (2) There was no significant difference in pH, PaCO 2, HCO 3- and lactic acid between the two groups during resuscitation. The PaO 2 in ACSV group was higher than that in IPPV group, and the difference was statistically significant at 4 and 7 min. (3) The success rate of resuscitation in both groups was 83.3%, and there was no significant difference in SV and GEF before and after resuscitation. (4) After resuscitation, cTnI, NSE, ALT, Cr, iFABP and other indexes in ACSV group were lower than those in IPPV group, and there were statistically significant differences in cTnI at 24 h after resuscitation, ALT at 2 h and 24 h after resuscitation, and IFABP at 4 h and 24 h after resuscitation (all P<0.05). Conclusions:This study preliminarily suggested that the novel ACSV could significantly improve the oxygen supply level during cardiopulmonary resuscitation in pigs, while keeping the compression efficiency unchanged, avoiding hyperventilation, and reducing multiple organ damage after resuscitation, which is worthy of further study.

Objective:To investigate the expressions of MUC1, MUC4, MUC5AC and MUC16 in patients with first diagnosis of dry eye and their correlation with dry eye symptoms and signs.Methods:A cross-sectional study was conducted.Sixty-nine dry eye patients (69 eyes) as dry eye group and 40 normal volunteers (40 eyes) as normal control group were recruited in Xiamen Eye Center of Xiamen University, Beijing Tongren Hospital, West China Hospital of Sichuan University and Shanghai Puotuo District Center Hospital from December 2016 to May 2018.Symptoms were evaluated by Chinese dry eye questionnaire, Ocular Surface Disease Index (OSDI) and Dry Eye-Related Quality-of-Life Score Questionnaire (DEQS). Signs were assessed by tear film breakup time (TBUT), keratoconjunctival fluorescein sodium staining, and Schirmer I test.Conjunctival cells were collected by conjunctival impression cytology.The expression levels of MUC1, MUC4, MUC5AC and MUC16 mRNA in the two groups were determined by real-time fluorescence quantitative PCR.The correlation between the mRNA levels of conjunctival mucins and dry eye symptoms and signs were analyzed by Spearman correlation analysis.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committees of Xiamen Eye Center of Xiamen University (No.2017003), Beijing Tongren Hospital, Capital Medical University (No.TREC2016-29), West China Hospital of Sichuan University (No.2016310) and Shanghai Puotuo District Center Hospital (No.PTEC-A-2016-18-1). Written informed consent was obtained from each subject before any medical examination.Results:The expression levels of MUC1 and MUC16 mRNA in dry eye patients were 3.277(0.568, 5.790) and 1.815(1.048, 3.694), which were higher than 1.055(0.550, 2.010) and 1.024(0.541, 1.965) in normal control group (Z=819.00, P=0.008; Z=861.00, P=0.002). According to OSDI scores, MUC1 was mainly increased to 3.277(1.161, 6.226) in mild to moderate (12-32 points) dry eye patients (Z=9.04, P=0.029), and MUC16 was mainly increased to 1.968(1.074, 3.726) in severe (>32 points) dry eye patients (Z=12.24, P=0.007). MUC1 expression was positively correlated with TBUT, and was negatively correlated with corneal staining scoring and keratoconjunctival staining scoring ( r s=0.270, P=0.025; r s=-0.331, P=0.006; r s=-0.325, P=0.007). MUC16 expression was positively correlated with TBUT, and was negatively correlated with blurred vision scoring, symptom exacerbation scoring during reading, impact scoring of driving at night, impact scoring of computer and impact scoring of TV use ( r s=0.249, P=0.039; r s=-0.359, P=0.047; r s=-0.370, P=0.034; r s=-0.558, P=0.016; r s=-0.498, P=0.006; rs=-0.515, P=0.002). Conclusions:The gene expressions of MUC1 and MUC16 are higher in conjunctiva of dry eye patients.MUC1 mRNA expression is related to patients' signs.MUC16 mRNA expression is related to the quality of life of patients.

Objective:To evaluate the safety and efficacy of a novel domestic extracorporeal membrane oxygenation (ECMO) mainframe in a porcine model, and to provide the basis for further clinical application.Methods:Five domestic healthy male white pigs, weighing (51±4) kg, were selected. The ECMO system was established by using a novel ECMO mainframe with imported membrane oxygenator and pipeline, and continued to run for 72 hours. ECMO parameters are as follows: veno-arterial ECMO, centrifugal pump speed 3 000-3 500 r/min, continuous infusion of heparin anticoagulation to maintain the activate clotting time (ACT) of 140-200 s. Real-time monitoring of speed, flow, pressure before pump, pressure after pump, pressure after membrane and other equipment parameters, and the equipment performance was scored. The changes of hemodynamics, blood lactic acid and blood routine were monitored dynamically. Repeated measures analysis of variance was used to compare different time points within the group. At the end of the experiment, the thrombosis in the pump head and oxygenator was observed. The animals were sacrificed to obtain the tissue samples of the main organs for gross observation and pathological injury evaluation.Results:All animals successfully ran the ECMO system for 72 hours. (1) The centrifugal pump speed should be maintained at 3 029-3 483 r/min, the flow rate was maintained at 2.24-2.60 L/min, The pressure before the pump between minus 107.57 and minus 31.86 mmHg, the pressure after the pump was 197.50-282.43 mmHg, and the pressure after the membrane was 178.71-261.5 mmHg, all were in the normal range, and there was no significant difference between different time points (all P>0.05). The performance scores of the mainframe were all 4 points or above, indicating that the use requirements were met. (2) The heart rate of the animals was 50-80 beats /min, the mean arterial pressure was 85-115 mmHg, and the lactic acid was 0.996-2.25 mmol/L, all within the normal range, and there was no significant difference between different time points (all P>0.05). The free hemoglobin was 8.98-16.39 mg/L, and the hemoglobin was 6.58-7.52 g/L, both within a reasonable range, and there was no significant difference between different time points (all P>0.05). The platelet count was 69.6-231.6×10 9/L, and showed a continuous downward trend ( P<0.05). ACT was maintained at 135-169 s, which was within the target range, and there was no significant difference between different time points ( P<0.05). (3) At the end of the experiment, there was no obvious thrombosis in the pump head and oxygenator, no obvious thrombosis or infarction in the heart, brain, liver, lung and kidney, and no obvious hemorrhage or necrosis under the microscope. Conclusions:The ECMO established by the novel domestic ECMO mainframe combined with imported membrane oxygenator and pipeline ran smoothly for 72 hours, achieving the target of effect and safety.

Objective:To analyze the clinical manifestations and signs of the first diagnosed dry eye patients, and to explore the concordance between the Chinese dry eye diagnostic criteria and the Asian dry eye diagnostic criteria.Methods:A cross-sectional multicenter study was conducted.One hundred and forty-one eyes of 141 patients who were diagnosed as dry eye for the first time were included in Xiamen Eye Center of Xiamen University, Beijing Tongren Hospital, West China Hospital of Sichuan University and Shanghai Putuo District Center Hospital from December 2016 to May 2018.All patients completed the Chinese Dry Eye Questionnaire, Ocular Surface Disease Index (OSDI) and Dry Eye-Related Quality-of-life Score Questionnaire (DEQS) to evaluate the symptoms of dry eye.Tear film breakup time (BUT), keratoconjunctival fluorescein staining, meibomian gland morphology and function examination, and Schirmer Ⅰ test were performed to evaluate dry eye signs and the association between dry eye symptoms and signs.The eyes were divided into corneal staining positive and negative group according to the presence or absence of corneal fluorescein staining, and the dry eye symptoms of the two groups were assessed by the three questionnaires.The eyes were divided into tear-deficient dry eye, evaporative dry eye, mixed dry eye and abnormal tear dynamics dry eye to compare the difference of dry eye signs among the groups.This study adhered to the Declaration of Helsinki.The study protocol complied with Chinese regulations and rules on clinical trial research and was approved by Ethics Committees of Xiamen Eye Center of Xiamen University (No.2017003), Beijing Tongren Hospital, Capital Medical University (No.TREC2016-29), West China Hospital of Sichuan University (No.2016310) and Shanghai Putuo District Center Hospital (No.PTEC-A-2016-18-1). Written informed consent was obtained from patients before entering the cohort.Results:The total score of Chinese Dry Eye Questionnaire, OSDI questionnaire and DEQS questionnaire was 12.00(7.00, 16.00), 25.00(17.50, 36.93) and 32.02(15.77, 52.34), respectively.It was found that 130 eyes (92.2%) had dryness, and 109 eyes (77.3%) had ocular fatigue and 108 eyes (76.6%) had foreign body sensation.Dryness, foreign body sensation, photophobia and poor vision were weakly positively correlated with corneal staining ( r=0.177、0.297、0.172, all at P<0.05). Pain, photophobia and poor vision were negatively correlated with tear secretion ( r=-0.178, -0.197, -0.174; all at P<0.05). It was found that 43.3% of dry eye patients had used visual display terminals.Among the 141 eyes, 75 eyes (53.2%) were with over evaporation dry eye, 43 eyes (30.5%) with mixed dry eye, 18 eyes (12.8%) with aqueous-deficient dry eye and 3 eyes (2.1%) with abnormal tear dynamics dry eyes. Conclusions:Initial diagnosis of dry eye patients is mainly mild to moderate.Dry eye signs and symptoms are correlated.Over evaporation dry eye is the most common type of dry eye.The concordance between the Chinese dry eye diagnostic criteria and the Asian Dry Eye Society diagnostic criteria reaches 97.2%.

Objective:To investigate the correlation between the prolongation of the QTc interval and carotid atherosclerosis in elderly patients with type 2 diabetes mellitus(T2DM).Methods:CIinical data of 212 elderly patients with T2DM admitted to our hospital from February 2016 to February 2019 were retrospectively collected.Based on carotid intima-media thickness(CIMT), patients were divided into the CIMT≥1.0 mm group(n=110)and the CIMT<1.0 mm group (n=102). Meanwhile, patients were divided into the prolonged QTc interval group(QTc interval>440 ms, n=50)and the normal QTc interval group(QTc interval≤440 ms, n=162), base on the adjusted QTc interval.General clinical data were compared between the groups, and the logistic regression equation was used to analyze the related factors for carotid atherosclerosis.Results:Higher values of age, duration of disease, systolic blood pressure(SBP), fasting plasma glucose(FPG), triglycerides(TG), creatinine(Cr), uric acid and C-reactive protein(CRP)were found in the CIMT≥1.0 mm group than in the CIMT<1.0 mm group( P<0.05). The QTc interval was longer in the CIMT≥1.0 mm group than in the CIMT<1.0 mm group[(419.2 ± 42.6) ms vs. (396.5 ± 45.2) ms, t=3.849, P<0.01]. CIMT was greater in the prolonged QTc interval group than in the normal QTc interval group[(1.2± 0.3)mm vs.(0.9±0.3) mm, t=6.956, P<0.01]. The detection rates of carotid atherosclerosis, intimal thickening and atheromatous plaques were higher in the prolonged QTc interval group than in the normal QTc interval group( 76.0% or 38 vs. 44.4% or 72, 32.0% or 16 vs.18.5% or 30 and 44.0% or 22 vs.25.9% or 42, respectively, χ2=15.239, 4.087 and 5.922, P<0.05). Pearson’s correlation analysis showed that CIMI was positively correlated with age, duration of disease, SBP, FPG, TG, Cr, uric acid, CRP and QTc interval( P<0.05). Multivariate logistic regression showed that the risk of carotid atherosclerosis in patients with QTc interval>440 ms was 1.761 times higher than that in patients with QTc≤440 ms( OR=1.761, 95% CI: 1.460-3.126, P<0.01). Conclusions:QTc interval prolongation is correlated with carotid atherosclerosis in elderly patients with T2DM, and attention should be paid to the QTc interval on the electrocardiogram, which is helpful to assess the risk of carotid atherosclerosis in elderly T2DM patients.

Objective:Analysis of clustering characteristics of coronavirus disease 2019 (COVID-19) in Guangdong Province.Methods:The COVID-19 cases in Guangdong Province onset from January 1 to February 29, 2020 were collected from Chinese information system for disease control and prevention and Emergency Public Reporting System. Obtain the epidemiological survey data of the cluster epidemic situation, and clarify the scale of cluster epidemic situation, the characteristics of the index cases, family and non-family subsequent cases. Calculate serial interval according to the onset time of the index cases and subsequent cases, secondary attack rate based on the close contacts tracking results, the characteristics of different cases in the clustered epidemic were compared.Results:A total of 283 cluster were collected, including 633 index cases, 239 subsequent cases. Families are mainly clustered, the total number involved in each cluster is in the range of 2-27, M( P25, P75) are 2.0 (2.0, 4.0). During January 15 to February 29, the secondary attack rate is 2.86% (239/8 363) in Guangdong Province, the family secondary attack rate was 4.84% (276/3 697), and the non-family secondary attack rate was 1.32% (61/4 632). According to the reporting trend of the number of cases in Guangdong Province, it can be divided into four stages, the rising stage, the high platform stage, the descending stage and the low level fluctuation period. The secondary attack rate of the four stages were 3.5% (140/3 987), 2.3% (55/2 399), 2.6% (37/1 435), 1.3% (7/542), respectively. The difference was statistically significant ( P=0.003). Conclusion:COVID-19 cluster mainly occurs in families in Guangdong Province. The scale of the clustered epidemic was small; the serial interval was short; and the overall secondary attack rate was low.

Objective:Analysis of clustering characteristics of coronavirus disease 2019 (COVID-19) in Guangdong Province.Methods:The COVID-19 cases in Guangdong Province onset from January 1 to February 29, 2020 were collected from Chinese information system for disease control and prevention and Emergency Public Reporting System. Obtain the epidemiological survey data of the cluster epidemic situation, and clarify the scale of cluster epidemic situation, the characteristics of the index cases, family and non-family subsequent cases. Calculate serial interval according to the onset time of the index cases and subsequent cases, secondary attack rate based on the close contacts tracking results, the characteristics of different cases in the clustered epidemic were compared.Results:A total of 283 cluster were collected, including 633 index cases, 239 subsequent cases. Families are mainly clustered, the total number involved in each cluster is in the range of 2-27, M( P25, P75) are 2.0 (2.0, 4.0). During January 15 to February 29, the secondary attack rate is 2.86% (239/8 363) in Guangdong Province, the family secondary attack rate was 4.84% (276/3 697), and the non-family secondary attack rate was 1.32% (61/4 632). According to the reporting trend of the number of cases in Guangdong Province, it can be divided into four stages, the rising stage, the high platform stage, the descending stage and the low level fluctuation period. The secondary attack rate of the four stages were 3.5% (140/3 987), 2.3% (55/2 399), 2.6% (37/1 435), 1.3% (7/542), respectively. The difference was statistically significant ( P=0.003). Conclusion:COVID-19 cluster mainly occurs in families in Guangdong Province. The scale of the clustered epidemic was small; the serial interval was short; and the overall secondary attack rate was low.