Unusual outbreak of influenza A in a Wyoming nursing home

An explosive outbreak of Influenza A (H3N2) occurred during early February 1985 among the 55 residents of a nursing home in Douglas, Wyoming. Thirty of the 55 (55%) had febrile respiratory illnesses. Thirty-six (65%) had received influenza vaccine. The attack rate was 84% in unvaccinated and 39% in vaccinated persons. Vaccine efficacy was estimated to be 54%. There were eight cases of pneumonia in unvaccinated and four in vaccinated persons, three deaths in unvaccinated and one death in vaccinated persons. Complement fixation and hemagglutination inhibition tests on sera from 47 residents confirmed the diagnosis of Influenza A in the great majority of individuals, and furthermore showed very low levels of antibody for the Influenza A H1N1 and Influenza B components of the vaccine.     

Influenza outbreak detection and control measures in nursing homes in the United States

OBJECTIVE: To evaluate the use of influenza vaccine, rapid influenza testing, and influenza antiviral medication in nursing homes in the US to prevent and control outbreaks. METHODS: Survey questionnaires were sent to 1017 randomly selected nursing homes in nine states. Information was collected on influenza prevention, detection and control practices, and on outbreaks during three influenza seasons (1995-1998). RESULTS: The survey response rate was 78%. Influenza vaccine was offered to residents and staff by 99% and 86%, respectively, of nursing homes. Among nursing homes offering the influenza vaccine, the average vaccination rate was 83% for residents and 46% for staff. Sixty-seven percent of the nursing homes reported having access to laboratories with rapid antigen testing capabilities, and 19% reported having a written policy for the use of influenza antiviral medications for outbreak control. Nursing homes from New York, where organized education programs on influenza detection and control have been conducted for many years, were more likely to have reported a suspected or laboratory-confirmed influenza outbreak (51% vs 10%, P = .01), to have access to rapid antigen testing for influenza (92% vs 63%, P = .01), and to use antivirals for prophylaxis and treatment of influenza A for their nursing home residents (94% vs 55%, P = .01) compared with nursing homes from the other eight states. CONCLUSIONS: Influenza outbreaks among nursing home residents can lead to substantial morbidity and mortality when prevention measures are not rapidly instituted. However, many nursing homes in this survey were neither prepared to detect nor to control influenza A outbreaks. Targeted, sustained educational efforts can improve the detection and control of outbreaks in nursing homes.     

Treatment of an influenza A outbreak in a teaching nursing home. Effectiveness of a protocol for prevention and control

The safety and efficacy of current ACIP guidelines for the prevention and control of influenza in nursing home populations are uncertain. An outbreak of influenza A/Sichuan (H3N2) in a teaching nursing home during 1988 gave us the opportunity to evaluate the effectiveness of an influenza vaccination and amantadine prophylaxis protocol. Over 13 days, 12 of 60 residents developed influenza. Prior influenza vaccination had been given to 94% of the residents. Protection from infection occurred in those tested who had antibody levels greater than or equal to 1:16 to the A/Leningrad (H3N2) antigen contained in the standard 1987-88 trivalent vaccine. However, five of 17 vaccinated residents who were tested had antibody levels less than or equal to 1:16 at the start of the outbreak. Amantadine (less than or equal to 100 mg/day) was given to all but one resident starting on the third day of the outbreak, and to employees starting on the sixth day of the outbreaks. Seven residents developed illness after the start of amantadine, although amantadine appeared to ameliorate their symptoms. Although amantadine was generally well tolerated by residents, employees receiving amantadine identified a high incidence of side effects and only 44% of employees took at least 70% of the prescribed amantadine. In our opinion, early detection and protocol-directed intervention probably abated a more severe influenza outbreak. Therefore we support existing recommendations that formal nursing home policies be established to ensure that residents and employees receive annual influenza vaccine and that chemoprophylaxis be used when outbreaks of influenza A are suspected.     

Effect of Influenza Vaccination of Nursing Home Staff on Mortality of Residents: A Cluster-Randomized Trial

OBJECTIVES: To evaluate the effect of staff influenza vaccination on all-cause mortality in nursing home residents.
DESIGN: Pair-matched cluster-randomized trial.
SETTING: Forty nursing homes matched for size, staff vaccination coverage during the previous season, and resident disability index.
PARTICIPANTS: All persons aged 60 and older residing in the nursing homes.
INTERVENTION: Influenza vaccine was administered to volunteer staff after a face-to-face interview. No intervention took place in control nursing homes.
MEASUREMENTS: The primary endpoint was total mortality rate in residents from 2 weeks before to 2 weeks after the influenza epidemic in the community. Secondary endpoints were rates of hospitalization and influenza-like illness (ILI) in residents and sick leave from work in staff.
RESULTS: Staff influenza vaccination rates were 69.9% in the vaccination arm versus 31.8% in the control arm. Primary unadjusted analysis did not show significantly lower mortality in residents in the vaccination arm (odds ratio=0.86, P =.08), although multivariate-adjusted analysis showed 20% lower mortality ( P =.02), and a strong correlation was observed between staff vaccination coverage and all-cause mortality in residents (correlation coefficient=−0.42, P =.007). In the vaccination arm, significantly lower resident hospitalization rates were not observed, but ILI in residents was 31% lower ( P =.007), and sick leave from work in staff was 42% lower ( P =.03).
CONCLUSION: These results support influenza vaccination of staff caring for institutionalized elderly people.     

Effectiveness of influenza vaccine when given during an outbreak of influenza A/H3N2 in a nursing home

An explosive outbreak of influenza A/H3N2 began in a nursing home in the Denver area early in November, 1987. Residents had not been vaccinated at that time. Vaccine was administered on November 11th. Two weeks after the vaccine was given, the attack rate differed between the vaccinated and unvaccinated individuals. There were 40 cases of influenza among the 98 elderly residents, 12 cases of pneumonia, and seven deaths. Vaccine efficacy two weeks after it was given was estimated to be 65.4% in preventing clinical illness. There were no cases of pneumonia and no deaths among people who were vaccinated more than two weeks before. The virus was identified as influenza A by complement fixation tests with convalescent sera from 16 individuals who had been ill. Many also had hemagglutination inhibition titers for A/Colorado/1/87, which were as high as titers for A/Leningrad/87. A/Colorado/1/87 closely resembled A/Sichuan/87.     

Effectiveness of influenza vaccination in prevention of influenza-like illness among inhabitants of old folk homes

The aims of the study were to determine the attack rate of influenza-like illness among inhabitants of five old folk homes nationwide using influenza vaccine as a probe and the effectiveness of influenza vaccination in prevention of influenza-like illness. We conducted a nonrandomized, single-blind placebo control study from June 2003 to February 2004. VAXIGRIP(R) 2003 Southern hemisphere formulation was used. Among 527 subjects, the attack rates of influenza-like illness in the influenza vaccine group were 6.4, 4.6 and 2.4% during the first, second and third 2-month periods, respectively. The attack rates of influenza-like illness in the placebo group were 17.7, 13.8 and 10.1%. Influenza vaccination reduced the risk of contracting influenza-like illness by between 14, and 45%. The vaccine effectiveness in reducing the occurrence of influenza-like illness ranged from 55 to 76%, during the 6-month study followup. The presence of cerebrovascular diseases significantly increased the risk of influenza-like illness (p < 0.005). Vaccine recipients had fewer episodes of fever, cough, muscle aches, runny nose (p < 0.001) and experience fewer sick days due to respiratory illness. Subjects who received influenza vaccination had clinically and statistically significant reductions in the attack rate of influenza-like illness. Our data support influenza vaccination of persons with chronic diseases and >50 year olds living in institutions.     

Protective efficacy of combined live intranasal and inactivated influenza A virus vaccines in the elderly.

OBJECTIVE: To evaluate the efficacy of adding intranasal live attenuated cold-adapted influenza A vaccine to inactivated influenza vaccine to prevent influenza A in elderly residents of long-term-care institutions. DESIGN: Randomized, double-blind, placebo-controlled study conducted over 3 years. SETTING: Three large nursing homes. PARTICIPANTS: A total of 523 residents of nursing homes (mean age, 84.2 years). INTERVENTIONS: All participants received trivalent inactivated influenza vaccine parenterally and were randomly assigned to receive either live attenuated influenza A (H3N2) virus vaccine or placebo intranasally. MEASUREMENTS: Laboratory-documented influenza A was defined as a respiratory illness plus isolation of influenza A virus from nasal secretions, significant serologic response, or both. Participants were considered to have been exposed to influenza A if they resided in an institution in which cases of influenza A were documented. Outbreak-associated illnesses were defined as those occurring between the first and last isolation of influenza virus from within the institution, +/- 3 days. RESULTS: Participants who received intranasal vaccine and were subsequently exposed to influenza A had significantly lower rates of laboratory-documented influenza A (9 of 162 vaccine recipients compared with 24 of 169 placebo recipients; vaccine protective efficacy, 60.6%; 95% CI, 18% to 82%), outbreak-associated respiratory illnesses (13 of 162 vaccine recipients compared with 34 of 169 placebo recipients; vaccine protective efficacy, 56.8%; CI 23% to 76%), and outbreak-associated influenza-like illnesses (6 of 162 vaccine recipients compared with 18 of 169 placebo recipients; vaccine protective efficacy, 65.0%; CI 17% to 86%). CONCLUSIONS: Intranasal immunization with live attenuated influenza A virus vaccine provided additional protection against influenza A when added to parenteral trivalent inactivated influenza vaccine among elderly nursing home residents.     

The roles of vaccination and amantadine prophylaxis in controlling an outbreak of influenza A (H3N2) in a nursing home

An outbreak caused by influenza A/Philippines/2/82 (H3N2)-like viruses occurred in a partially vaccinated nursing home population in January 1985. During the first six days of the outbreak, 14 (25%) of 55 residents developed influenzalike illness. The risk of illness was most strongly associated with undetectable levels of antibody against the epidemic strain, with unvaccinated case-patients having more severe illnesses and a higher rate of hospitalization than vaccinated case-patients (5/8 vs 0/6). During the period of amantadine hydrochloride prophylaxis (100 mg/d) from days 7 to 35, only two (5%) of the remaining 41 residents became ill, even though 11 (27%) had no detectable antibody. Serum amantadine levels obtained on day 35 ranged from 117 to 737 ng/mL (mean 309 ng/mL), similar to therapeutic levels documented in younger adults who have taken the standard regimen of 200 mg/d; there were few clinically significant side effects. These findings illustrate the benefits of influenza vaccination and support the use of amantadine hydrochloride at a dosage of 100 mg daily for outbreak control among elderly persons.     

An outbreak caused by the SARS-CoV-2 Delta (B.1.617.2) variant in a care home after partial vaccination with a single dose of the COVID-19 vaccine Vaxzevria,London, England,April 2021

We investigated a COVID-19 outbreak of the SARS-CoV-2 Delta variant of concern in a London care home, where 8/21 residents and 14/21 staff had received a single dose of Vaxzevria (ChAdOx1-S; AstraZeneca) vaccine. We identified 24 SARS-CoV-2 infections (16 residents, 8 staff) among 40 individuals (19 residents, 21 staff); four (3 residents, 1 staff) were hospitalised, and none died. The attack rate after one vaccine dose was 35.7% (5/14) for staff and 81.3% (13/16) for residents.     

Experience with oseltamivir in the control of a nursing home influenza B outbreak.

Oseltamivir prophylaxis was very effective in protecting nursing home residents from ILI and in halting this outbreak of influenza B. A portion of the total ILI cases may have been due to influenza A, as this strain was isolated in one resident. The 10% attack rate in this facility, controlled with oseltamivir, compares favourably with another influenza B outbreak in a similar facility in the same region, over the same time frame (ILI onset 27 December to 17 January). Oseltamivir prophylaxis was not used to manage this second outbreak of laboratory-confirmed influenza B. Of the 236 residents, 45 developed ILI for an overall attack rate of 19%, nearly double the rate in the oseltamivir-controlled setting (10%). While oseltamivir was effective in controlling influenza B in this outbreak, further experience and evaluation is required before it can be routinely recommended for prophylaxis of influenza in nursing home outbreaks. Although earlier attempts by others using oseltamivir in the control of influenza A outbreaks have also met with success, it is not yet licensed for this purpose. Compared to amantadine, oseltamivir has a relatively high cost for the control of influenza A outbreaks and this may continue to limit its wider acceptance. The cost-effectiveness of oseltamivir in the control of influenza B outbreaks needs to be specifically addressed given the typically milder nature of influenza B strains. However, such a distinction is not clinically reliable and elderly residents of long-term care facilities remain vulnerable to serious complications associated with influenza infection in general. An alternate agent for influenza chemoprophylaxis that is effective against both influenza A and B, is easily administered and has few side effects, could greatly enhance current prevention and control measures and warrants serious assessment. The spread of this outbreak from the geographically separate ward to other areas of the facility in which residents had not received prophylaxis, underscores the likely role of staff as a vehicle for transmission during facility outbreaks. While accurate staff ILI rates could not be determined, their immunization rates were low, and many staff were ill during the outbreak. Isolation of residents with ILI and prophylaxis of non-ill residents on the initial outbreak wards was insufficient to prevent the spread of the outbreak, although it was subsequently halted once prophylaxis was extended to all residents. In view of the uncertainty over this medication's widespread use, in the absence of licensure or previous studies demonstrating its effectiveness in the prophylaxis and control of influenza B outbreaks, initiation of oseltamivir prophylaxis was staggered by ward. In a declared influenza A outbreak, the protocol in a long term care facility is to initiate amantadine prophylaxis on all residents, rather than ward-by-ward. While anti-viral prophylaxis may be an effective secondary control measure in the management of influenza outbreaks, optimal primary prevention would be more effective. This would require increased vaccine coverage of residents and particularly of staff, who play an important role in the importation and transmission of influenza within these facilities.     

An outbreak of giardiasis in a nursing home with evidence for multiple modes of transmission

During a 6-w period from 20 April through 7 June 1986, an outbreak of giardiasis occurred in residents and employees of a nursing home and children participating in day care at the nursing home. Eighty-eight cases of giardiasis (defined by presence of clinical symptoms or results of stool examination) were identified from groups associated with the nursing home including 35 in nursing home residents, 15 in children in day care, and 38 in employees (including kitchen staff and child care providers). Multiple modes of transmission of Giardia lamblia, including food-borne and person-to-person transmission, occurred for these groups. Evidence of transmission by food included a significant association between sandwich consumption and illness in nursing home staff (P = .04) and a significant lack of illness among nursing home residents who consumed only a pureed diet (P = .007), where all food items are cooked before serving. The primary case among the food handlers, whose illness began in mid-April, had an infected child in the day care center. Person-to-person transmission is supported by a significant association between illness and physical contact with children from the day care facility through an "adopted grandparent" program (P = .03). This is the first reported outbreak of giardiasis in a nursing home, and these findings have implications for disease control in other facilities that combine child day care and care of the elderly.     

Introduction of the BNT162b2 vaccine during a COVID-19 nursing home outbreak

BackgroundCoronavirus disease 2019 (COVID-19) outbreaks often occur in nursing homes and prompt frequent surveillance testing for SARS-CoV-2. A single dose of the BNT162b2 vaccine reduces viral load and transmission. In this study, we describe the real-world efficacy of BNT162b2 single-dose vaccination during a COVID-19 outbreak at a Veterans Affairs Community Living Center (CLC).MethodsFrom 12/2/20 to 5/14/21, twice weekly antigen testing was used to detect COVID-19 among 146 residents at the CLC. Residents without a prior history of COVID-19 who agreed to immunization were vaccinated with the BNT162b2 vaccine on 12/16/20 and 1/6/21. Single-dose vaccine efficacy was determined for days 1-21 and days 14-21 after the first vaccine dose.ResultsThe outbreak occurred from 12/2/20 to 1/7/21 with an attack rate of 30.8% (45/146); 46.7% (21/45) of the cases were due to asymptomatic COVID-19. One unit accounted for 77.8% (35/45) of the cases. In the vaccine analysis, 116 residents were a median age of 74.5 years and 93.1% (108/116) had ≥ 1 comorbid condition. Between the first and second dose, 15.5% (15/97) of vaccinated residents, and 21.2% (4/19) of unvaccinated residents developed COVID-19 (P = .81). One week after the second dose, no cases of COVID-19 occurred.ConclusionsAlbeit limited by the small numbers, a single dose of the BNT162b2 vaccine was not efficacious at preventing COVID-19 during this nursing home outbreak.     

Amantadine usage for influenza A during an influenza outbreak in a nursing home

An outbreak of an influenza like illness was found in a nursing home in Fukuoka in January, 1999. Results of hemagglutinin inhibition tests with paired sera of patients and rapid diagnosis kit for influenza A indicated that an influenza A (H3N2) outbreak had occurred. A total of 15 patients with influenza like illness from one residential area of the nursing home were administered amantadine, 100 mg per day for five days. Clinical records of 264 residents were surveyed retrospectively from the tenth to the thirty-first of January, 1999. Influenza like illness was found in 112 residents (42.4%). The incidence of influenza like illness differed by residential area, ranging from 27.6% to 54.0%. The mean duration of fever was 3.6 days among patients administered amantadine. The mean duration was 4.4 days for patients not administered amantadine. The incidence of influenza like illness decreased rapidly after amantadine administration in the residential area where amantadine administration was done. These results suggest that amantadine is effective in mitigating influenza symptoms in the elderly. Amantadine may be useful for diminishing the influence of influenza A outbreaks in nursing homes.     

A case-control study of influenza vaccine effectiveness among Malaysian pilgrims attending the Haj in Saudi Arabia.

OBJECTIVES: To determine influenza vaccine effectiveness against clinically defined influenza-like illness among Malaysian pilgrims attending the Haj in Saudi Arabia. METHODS: During February and March 2000, the authors conducted an unmatched case-control study. Case patients were identified at one of five hotel clinics, while controls were residents of these hotels who had not attended a clinic. Results: Among 820 case patients--84% of whom had received antibiotics--and 600 controls, the adjusted vaccine effectiveness against clinic visits for influenza-like illness was 77% (95% confidence interval: 69, 83), and that against receipt of antibiotics was 66% (95% confidence interval, 54, 75). The vaccine did not prevent clinic visits for non-influenza-like upper respiratory tract illness (adjusted vaccine effectiveness, 20%; 95% confidence interval: -24, 49). CONCLUSIONS: Influenza vaccine was effective in preventing clinic visits for influenza-like illness and antibiotic use. Pilgrims traveling to the Haj in Saudi Arabia should consider influenza vaccination use.     

Standing orders for influenza vaccination increased vaccination rates in inpatient settings compared with community rates

BACKGROUND: Hospitalization of older adults during the period of influenza vaccination in the fall of each year presents a barrier to immunization against influenza. This study evaluates a program using standing orders for influenza vaccination to increase vaccination rates among hospitalized older adults and to determine the effect of vaccination on readmission rates for influenza-like illness. METHODS: An influenza vaccination program using a standing order policy was implemented to vaccinate all consenting persons 65 years and older prior to hospital discharge. This was a prospective, single center, cohort study in a tertiary care university teaching hospital during an 8-week vaccination period in the fall of 1994 and follow-up during the subsequent influenza season. The vaccination status of each patient was recorded as no vaccination, vaccination received in hospital, or vaccination in the community prior to or after the hospitalization. Hospital vaccination rates were compared with the rate of vaccination of older adults in the community. During the subsequent influenza season, the number of subjects reporting symptoms of influenza-like illness (ILI) or who were readmitted to hospital with influenza-related illness was compared in an analysis of vaccinated versus unvaccinated subjects. RESULTS: Seven hundred and sixty-one patients were interviewed, and 332 of these individuals had been vaccinated in the community prior to their hospital admission. Of the remaining 429 unvaccinated patients who were eligible for vaccination in the study, 171 were vaccinated in our immunization program, eight were vaccinated in the community after discharge, and 244 were not vaccinated. We were able to increase the absolute vaccination rate by 22%, when compared with community rates, with our immunization program. The number of subjects with ILI symptoms or readmission to hospital was too small to compare the vaccinated to the unvaccinated group in the study. CONCLUSIONS: An inpatient influenza immunization program using a standing order policy was able to target a particularly high-risk subset of persons 65 years and over who might otherwise have not received influenza vaccination.     

Efficacy of Influenza Vaccine in Elderly Persons in Welfare Nursing Homes: Reduction in Risks of Mortality and Morbidity During an Influenza A (H3N2) Epidemic

BACKGROUND: The effect of influenza vaccination on the occurrence and severity of influenza virus infection in a population residing in nursing homes was studied through a program by the Osaka Prefectural Government, which is the first and official support for influenza vaccination of the elderly population during an influenza A (H3N2) epidemic in JAPAN: METHODS: A cohort study located in the Osaka Prefecture, Japan, followed the outcomes of elderly nursing home residents who received influenza vaccinations (n = 10,739) in comparison with control subjects who did not receive influenza vaccinations (n = 11,723) and monitored clinically the onset of serious morbidity and mortality of influenza illness. Subjects were 22,462 persons older than 65 years who resided in 301 welfare nursing homes in the Osaka Prefecture, Japan during an influenza A (H3N2) epidemic in 1998 to 1999. RESULTS: Of 22,462 individuals living in 301 nursing homes, 10,739 received either one dose (2027 subjects) or two doses (8712 subjects) of inactivated, subunit trivalent influenza vaccine. Through the period from November 1998 to March 1999, there were 950 cases of influenza infection diagnosed clinically with cases by virus isolation and/or serology. There were statistically significantly fewer clinical cases of influenza, hospital admissions due to severe infection, and deaths due to influenza in the vaccinated cohort (256 cases, 32 hospital admissions, and one death) compared with the unvaccinated controls (694 cases, 150 hospital admissions, and five deaths). Vaccination was equally effective in those who received one dose of vaccine as in those who received two doses. No serious adverse reactions to vaccination were recorded. Thus, influenza vaccination is safe and effective in this population and should be an integral part of the routine care of persons aged 65 years and older residing in nursing homes. CONCLUSIONS: This study provides an analysis of the clinical efficacy of influenza vaccination in a large cohort of nursing home residents in JAPAN: Annual influenza vaccine administration requires the attention of all nursing home attendants, physicians, and public health organizations.     

An outbreak of nosocomial hepatitis B virus infection in a nursing home for the elderly in Antwerp (Belgium)

After notification of a case of fulminant hepatitis B virus (HBV) infection in a 83-year-old female resident of a nursing home to the Flemish Health Inspectorate, a seroepidemiological study and a retrospective cohort study were conducted among the 94 residents and 47 nursing staff to assess the extent of HBV transmission and to identify risk factors. Susceptible residents were vaccinated against HBV and their serological response to hepatitis B vaccination determined. From December 2002 to April 2003, five residents with acute hepatitis B infection were identified with an attack rate of 5.5% and a case fatality rate of 40%. Three other residents were identified as HBV surface antigen and e-antigen positive carrier. None of the nursing staff tested positive for acute HBV infection or HBV carriage. Diabetic patients who were exposed to a shared finger-stick device for blood sampling were 10.7 times more likely to contract an acute HBV infection (RR 10.7; 95% CI 1.3-91.3). Other potential risk factors were undergoing podiatric care and being exposed to the shared razor blade of the hairdresser. The transmission of the infection could be controlled by restricting the use of finger-stick capillary sampling devices to individual patients, assigning separate glucometers to individual patients and, implementation of standard infection-control recommendations like wearing gloves and performing hand hygiene by the nursing staff, assigning separate podiatric sets to individual patients. HBV vaccination of the residents with three doses of HBV vaccine has not induced a sufficient degree of protection. The outbreak stresses the need for appropriate and generally applied standard procedures in nursing homes to prevent bloodborne pathogens.     

Influenza vaccination for health-care workers who work with elderly people in institutions: a systematic review

Our aim was to review the evidence of efficacy and effectiveness of influenza vaccination of health-care workers in reducing cases of influenza-like illness, influenza, complications from influenza, death from influenza, and death from all causes among the elderly people they care for in institutions. We searched 11 electronic databases in any language and identified two cluster-randomised controlled trials with moderate risk of bias and one cohort study at high risk of bias that addressed our questions. Staff vaccination had a significant effect on influenza-like illness (vaccine effectiveness [VE] 86%, 95% CI 40-97%) only when patients were vaccinated too. If patients were not vaccinated, staff immunisation had no effect. Vaccinating health-care workers did not appear efficacious against influenza (RR 0.87, 95% CI 0.46-1.63). There was no significant effect of vaccination on lower respiratory tract infections: (RR 0.70, 95% CI 0.41-1.20). Deaths from pneumonia were significantly reduced (VE 39%, 95% CI 2-62%), as were deaths from all causes (VE 40%, 95% CI 27-50%). These findings must be interpreted in the light of possible selection, performance, attrition, and detection biases.     

Response to influenza vaccination in community and in nursing home residing elderly: relation to clinical factors

Intramuscular (IM) influenza vaccines are about 50% effective in preventing respiratory illness among the elderly. The aim of this study was to identify factors associated with immune response to influenza vaccination among nursing home and community-residing elderly. 114 nursing home (NHE) and 62 community residing elderly (CE) were vaccinated with a commercial IM vaccine. Serum antibodies were evaluated by HIA, and the impact of subjects' clinical characteristics on seroconversion was determined. Factors that were associated with low seroconversion among NHE, included: type II diabetes [for B/Harbin: p=0.044, OR 0.12, (CI: 0.015-0.94)], and antibody titer prior to vaccination A/(H1N1): p=0.03, OR 2.38, (CI: 1.09-5.22); A/(H3N2): p=0.015, OR 2.68 (CI: 1.22-5.92), B/Harbin: p=0.057, OR 4.46 (CI: 0.96-20.85)]. Factors that were associated with lower seroconversion CE elderly, included older age [A/(H1N1): p=0.008, OR 0.846, (CI 0.75-0.96), B/Harbin: p=0.016, OR 0.812, (CI:0.69-0.96)], and antibody titer prior to vaccination A/(H1N1): p=0.029, OR 4.08, (CI: 1.16-14.37); A/(H3N2): p<0.0001, OR 11.495 (CI: 3.18-41.55)]. There was no significant difference in seroconversion between nursing home residing elderly and community elderly. We conclude that Type-II diabetes and antibody titer>1:40 prior to vaccination are associated with reduced response to the influenza vaccination in nursing home elderly.