Mandatory Vaccination Against Influenza: Strategies for Compliance

By Kelly M. Pyrek

Experts say that vaccination of healthcare workers against influenza is one of the key ways to protect patients and boost occupational health, yet annually, infection preventionists engage in a battle of persuasion and politics to get better compliance rates at their institutions. One of the challenges is ensuring that healthcare workers are not working while being infected with the influenza virus; during outbreaks in healthcare settings, laboratory-confirmed influenza attack rates have been documented to be as high as 51 percent. Studies have demonstrated that influenza vaccination of healthcare personnel has decrease infection rates, and a growing body of evidence has shown that vaccination can improve patient outcomes in healthcare settings.

While many facilities are requiring vaccination as a condition of employment, others are finding creative ways to get healthcare workers to do what's right while protecting the individual's right to choose. We look at three different approaches recently undertaken and described in the literature.

Lisa Esolen, MD, systems director of infection control at Geisinger Health System in Danville, Pa., and her colleagues detailed their health system's requirement that unvaccinated workers wear a face mask in the presence of patients if they choose not to get vaccinated, in a study in the journal Infection Control and Healthcare Epidemiology. Esolen, et al. (2011) report that Geisinger, a major teaching hospital, achieved 95 percent compliance in 2009, and subsequently reached 90 percent and 92 percent compliance for two years.

"We had tried a variety of initiatives just as other health systems had but only reached a compliance rate of about 60 percent," Esolen says. "We felt that to exceed 90 percent compliance we needed a stronger approach."

As Esolen, et al. (2011) explain further, "After studying our options and the diversity within our 31-county employee population, Geisinger Health System (GHS) decided to transparently operationalize a face-masking requirement as the cornerstone of our 2009-2010 vaccination campaign. In so doing, we preserved a degree of healthcare worker (HCW) choice, protected patients, and achieved our goal in a very short time frame."

With the required-masking policy being pivotal to Geisinger's influenza campaign, Esolen, et al. (2011) say the policy needed to be enforceable, transparent, clearly defined and required accountability. An electronic template listing department employees was designed; adjacent to the employee name was the date of their vaccination, while non-vaccination resulted in a blank box. A star sticker was placed on the employee badge when vaccinated, thus ensuring general awareness of who received the vaccine and who therefore did or did not need to don a mask. Unvaccinated employees were instructed to place a mask around their neck at the start of every shift and lift it over their face when within 6 feet of a patient. A new mask was needed each shift or whenever it became moistened, soiled or torn. Geisinger managers were held accountable for enforcement and persistently non-compliant employees were disciplined. The program ran from Nov. 1 through March 31.

After defining the masking policy Esolen and her colleagues established a highly convenient vaccination process by increasing vaccination hours, placing vaccination stations at employee entrances and outside the cafeteria, and by decentralizing vaccine supplies with the recruitment of about 150 "flu team captains." These clinical department captains received flu kits that contained the vaccine, supplies, consent forms and stickers. Because of the pandemic situation at the time, employees were also required to receive the H1N1 vaccine to be exempted from the masking policy; this was acknowledged by a second star sticker on the employee identification badge.

As Esolen, et al. (2011) note, "Once the logistical issues regarding the masking policy were established and handled, the vaccination process itself was swift and smooth. This method achieved 90 percent to 92 percent vaccination compliance for two consecutive years. Furthermore, 92 percent of all vaccine dispensed in 2009 was given in a span of only four weeks, making 2009-2010 by far the most efficient vaccination year in the history of our health system. The 2010 season has duplicated this timeline with even higher compliance numbers. Though the 2009 compliance with nH1N1 vaccination was slightly lower, this mirrored the national trend while still being much higher than prior seasonal vaccine years. Like other facilities, GHS experienced unreliable and erratic nH1N1 supplies as well as employee concerns about vaccine safety."

The mask mandate could be construed as a stringent approach that would be unpopular with employees, and as Esolen, et al. (2011) acknowledge, "Some have questioned whether a masking policy unfairly stigmatizes those who have a medical contraindication to vaccination. With our program, these individuals were not singled out since there were others who chose to mask rather than be vaccinated. Also, as we did not consider this a punishment but a protection, the reason for being unvaccinated was irrelevant."

"There were a variety of reactions to our program, but they were mostly positive," Esolen says. "The unvaccinated folks who wore masks were not happy about this requirement but they were more content to wear a mask than get vaccinated and were glad to have that option. Having some degree of choice here made a huge difference." Esolen adds, "I think our approach was a happy medium. We wanted high compliance but also did not want employees to have a perception that leadership was aloof to the concerns or did not care if they stayed in their current job or left. We wanted our success to be one that the employees actively participated in and could be proud of."

Whether it was the desire to protect their patients or a desire to avoid mask usage that may have fueled personnels participation, Esolen remains philosophical about the end result. "I think it was many things. Certainly the fact that senior leadership chose this issue to focus on increased the awareness and importance of this initiative for the safety of our patients as well as our employees. Others were motivated to be vaccinated so as to avoid wearing a mask for nearly six months. In either case we achieved our goal which was patient and employee protection."

While Geisinger is a substantial health system, Esolen says she believes similar vaccination compliance results could be achieved in a smaller setting. "I think this system may work even better in a smaller system where peer pressure can be significant and employees who are tempted to not wear a mask when required may be more obvious. The critical factor here is that the masking policy have real teeth -- it must be clear who needs to don the mask and it much be enforced without hesitation. Supervisors have to know that they can be subjected to disciplinary action if they have variable compliance on their unit."

And as Geisinger's program is closely watched by other facilities hoping to boost their vaccination compliance rates, Esolen reports that she and her colleagues have received interesting feedback since their study was published. "I have since given a talk to several hospitals in the central Pennsylvania area at the request of our state department of health encouraging other health systems to adopt stricter programs. Most of the feedback has been supportive. Most other hospitals are attracted to giving some degree of an option to employees and not risking lengthy legal battles."

Esolen, et al. (2011) note, "Despite the clear result of achieving our goal in a short time frame, there may be other downstream advantages to this approach. Changing our healthcare culture to one of safety is a major focus when discussing quality care. But is culture best changed by a mandate? A process that requires the final acquiescence of our healthcare workers, that still inspires abounding team spirit and peer pressure, and that acknowledges all employees in the accomplishment could have unique value. Achieving high vaccination compliance by mandate may be a necessary approach. Achieving it in this multifaceted way may create a more enduring commitment on an individual level."

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Elizabeth L. Daugherty, MD, MPH, of the Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine in Baltimore, and colleagues, say that success of a stringent healthcare vaccination program hinges upon healthcare workers' understanding of it, as evidenced by the results of their recent survey of 928 hospital staff during the 2008-2009 influenza season. Although 91 percent of survey respondents with regular patient contact reported being vaccinated for influenza in the 2008-2009 season, just 60 percent reported consistent annual vaccination. Daugherty, et al. (2011) explain that, "Misinformation regarding hospital policies is widespread. Improvements in vaccination rates will likely require multifaceted, targeted efforts focused on specific influences on less adherent groups. The identified variability in influences on the decision to be vaccinated suggests possible targets for future interventions."

During the influenza season in early 2009, a voluntary, anonymous survey was distributed to staff; the 20-item survey assessed clinicians knowledge, attitudes, and beliefs related to both influenza vaccination in general and our hospitals specific vaccination policy in particular.

Daugherty, et al. (2011) report that of those surveyed, 75 percent completed the survey; 623 respondents reported regular patient contact, and 91 percent of those reported vaccination in the current influenza season. However, only 60 percent reported consistently receiving the vaccine every year. Of those who were vaccinated, 8 percent reported being vaccinated for the first time during that influenza season. Forty-two percent of respondents were unaware of the major change in hospital policy regarding vaccination. Influences on the decision to be vaccinated varied significantly between those who are regularly vaccinated and those with inconsistent vaccination habits. Attitudes toward hospital policy varied significantly by race and clinical role.

In the past, Johns Hopkins had offered the seasonal influenza vaccine to all employees free of charge for more than 15 years, but vaccination had never been required before. In an effort to improve vaccination rates, a policy of active declination was instituted in 2006. At the beginning of the 2008-2009 influenza season, the vaccine policy was changed to require that surgical masks be worn by those who declined vaccination when their responsibilities required them to be in close contact with patients at a distance of less than 6 feet). Also during the 2008-2009 flu season, a colored ID badge clip was distributed to each staff member who was vaccinated. The lack of a badge clip was intended to prompt supervisors to remind unvaccinated staff about the mask requirement, but no specific discipline was delineated for those who failed either to receive vaccine or to wear the recommended mask. The hospital communicated details about the changes in hospital policy through a variety of methods, including formal and informal meetings with nursing and physician leaders on departmental and, for nurses, unit-based levels.

The researchers found that a number of staff were unaware of the policy changes; most believed incorrectly that vaccination or wearing of a surgical mask was required regardless of whether the employee had contact with patients. A small percentage of staff members were unaware of the prominently advertised ID tags distributed to those who had been vaccinated so that they would be easily identifiable to their supervisors. More than one-quarter of staff were unaware that the hospital had an active declination policy.

Daugherty, et al. (2011) report that they found significant variability in factors influencing the decision to be vaccinated, based on whether the respondent received vaccine consistently each season or was inconsistent in his or her vaccine uptake. Of note, those who reported receiving vaccine every season were more likely than inconsistent vaccinees to believe that the vaccine protected them against flu and prevented the spread of flu to their patients or their families. Those who were inconsistent in their uptake were more likely to report that external factors such as the mask requirement or supervisor expectations were strong influences on their vaccination decision. Perception of supervisor and institutional expectations were found to be significantly more important among those with inconsistent vaccine practice. Furthermore, the significance of workplace expectations were found to vary by sex, race and professional role. When it comes to opinions about the vaccination policy, the researchers found that those with inconsistent vaccination practice were less likely to believe that the policy had an impact on influenza prevention and more likely to feel that the policy is unfair. Nurses were more likely than physicians and nonclinical staff to feel that the policy was unfair and put too much pressure on staff.

The researchers say that "despite aggressive, targeted publicity and notifications, we found that effective communication regarding hospital policy appeared to be lacking, potentially engendering confusion and furthering misperceptions and mistrust. This is exemplified by the significant proportion of healthcare workers who were unaware of policy changes and the fact that greater than 50 percent reported incorrectly that the policy applied to staff without patient contact. Such broad misconceptions of the policy further call into question whether institutions have been as effective as they may have hoped in communicating the rationale and importance of vaccination to staff." They add, "We also found that those who are consistently vaccinated tended to make their decisions on the basis of the belief that vaccination is effective at keeping them, their patients, and their families healthy. Although those who are inconsistent in their vaccine practice do report that vaccine effectiveness is important, they are more likely than those who are vaccinated regularly to be driven in their decision making by external requirements, such as mask wearing and supervisor or institutional expectations. Such findings suggest that although external inducements may impact behavior intermittently, as expected, they are less likely to have the ability to change behavior over the long term. Furthermore, the group that is inconsistently vaccinated is also more likely to believe that the policy is unfair and puts too much pressure on staff to participate. The combination, then, of a group that is less likely to think that the policy is effective and more likely to think that it is unfair may be a group at risk for increasing institutional mistrust and discontent."

There is still work to be done in assessing attitudes toward influenza vaccination. As Daugherty, et al. (2011) summarize, "Our findings suggest a need for more investigation of factors influencing healthcare worker beliefs about vaccine effectiveness in order to tailor policies and programs to address not just adherence but the drivers behind it. Although we agree that mandatory vaccination will likely significantly improve adherence, the perception of unfairness and excessive pressure on the part of the institution is not a trivial concern. Policies that foster trust, rather than mistrust and resentment, are likely to be far more effective in the long run. Further investigation is warranted to assist in the development of such policies."

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The following success story is significant not only because of the exceedingly high vaccination compliance rate among healthcare workers, but also because of the high rate of cooperation from affiliated physicians. Lynne V. Karanfil, RN, MA, CIC, of MedStar Health in Columbia, Md. and colleagues describe a mandatory program at MedStar Health, a regional healthcare organization that includes nine hospitals with approximately 25,000 healthcare workers and approximately 4,000 affiliated physicians.

As Karanfil, et al. (2011) explain, "With previous vaccination rates parallel to reported national rates of 54 percent among HCP, MedStar Health introduced a mandatory seasonal influenza vaccination program promulgated during the 2009-2010 influenza season. HCP and affiliated physicians were given an opportunity to apply for medical or religious exemptions. Non-compliant HCP were terminated. Non-compliant physicians had their privileges administratively suspended for the influenza season."

Healthcare worker compliance (both vaccinated and exempt) was 99.9 percent, while the influenza vaccination rate among healthcare workers was 98.5 percent. Just 0.01 percent of healthcare workers were terminated. Ninety-three percent of affiliated physicians were vaccinated while just 4 percent had their admitting privileges suspended during the influenza season.

Karanfil explains that leadership was responsible for the high vaccine uptake by physicians. "MedStar Healths Healthcare Epidemiology and Infection Control (HEIC) Task force, a multidisciplinary task force of infection control and infectious disease physicians, was challenged by Dr Thomas, chief medical officer and executive vice president of medical affairs, to be bold in our next steps in preventing healthcare associated infections," she says. "Dr. Thomas accepted our challenge, after HEIC developed a white paper that included the science supporting healthcare worker flu vaccination. The literature indicated a mandatory policy as a key success component. While we had support from executive leadership, the science is what won the physicians over!"

Knowing that the Maryland statewide average influenza vaccination rate among healthcare workers for the 2008-2009 season was 58.6 percent, Karanfil and colleagues set out to determine if a mandatory seasonal influenza vaccination policy would increase Medstar's rates of vaccination. As we will see, they achieved enormous compliance, and the success has been hard-won for Medstar. Its campaign to increase vaccination rates dates back to 2006, when MSH launched a corporate educational campaign which included emphasis placed on communication, a unique logo, and branding, focused on vaccinating a greater number of staff as a key component to pandemic planning. As Karanfil, et al. (2011) explain, "The rationale was that building the vaccination infrastructure early would enable MSH hospitals to deal more effectively with a potential pandemic. Every year since 2006, occupational health leaders have met to share best practices and strategies for increasing vaccination rates. While strides were made at some sites, the campaign was not considered a system-wide success despite numerous attempts to raise the vaccination rate through the modalities suggested in the literature. In 2007, the rate among our six acute-care hospitals was 47 percent. In 2008, the rate among our then eight hospitals was approximately 54 percent, with a range of 40 percent to 62 percent."

In 2008, MSH developed an infection control operating plan, including chartering the aforementioned HEICT which eventually endorsed the proposal that all healthcare workers, affiliated physicians, residents, volunteers, students, contractors and vendors be vaccinated with the seasonal influenza vaccine annually. In 2009, the MSH medical leadership approved the mandatory influenza vaccination program proposal. The vaccination requirement was defined as a patient safety and quality-of-care initiative that also protected overall public health.

"This was a patient-safety initiative," Karanfil emphasizes. "Anyone not vaccinated could potentially infect our patients. There was one standard at MedStar -- if you set foot on our premises during influenza season, you must be vaccinated. This is key for the health and safety of our patients. Our motto is 'Everyone Counts when it comes to flu prevention.'"

The Mandatory Influenza Vaccination Task Force crafted a policy dictating that failure to comply with the policy resulted in termination for healthcare workers and affiliated physicians who did not meet the policy expectations had their admitting privileges administratively suspended during the influenza season. Karanfil, et al. (2011) explain the program in detail: "An extensive communications plan and tool kit with a new brand concept were developed centrally and used by each business unit. The new theme emphasized that 'Everyone Counts.' Communications were based on learnings from the previous years vaccine compliance assessment. In 2008, seven of our hospitals required HCP to complete a computer-based learning module to obtain data on the reasons for influenza vaccine declination. Although 59 percent of the 13,709 respondents indicated that they were vaccinated, over 1,200 HCP reported that the vaccine would give them influenza, insisted that they were not at risk, or said that they did not want anything unnatural in their body. Another 24 percent reported that they did not feel it was necessary or said they were afraid of needles. These data are consistent with the numerous studies on why HCP do not undergo yearly vaccination, which includes perceptions of being healthy."

The variability of healthcare worker perceptions and attitudes toward vaccination can be challenging, and Karanfil explains how facilities can handle certain fallacies or fears about vaccination. "I surveyed nurses more than 18 years ago and found some of the reasons they did not get a flu vaccination included lack of education and communication," she says. "The same is reported in the literature. A key to our success is educating associates and medical staff about the myths and misconceptions of the influenza vaccination. We communicate the facts and significant patient safety benefits of vaccination on an annual basis, which includes articles, FAQs, online education programs, and new associate orientation. In addition, we find success in using a peer-to-peer vaccination program. Personally, I have found that when staff members see another staff member obtaining the vaccination, they are not as fearful and are more inclined to get vaccinated."

Medstar met any concerns head on, ensuring that plenty of collateral materials reached everyone who conducted business on their healthcare campus. As Karanfil, et al. (2011) explain further, "Letters regarding the new mandatory influenza vaccination program were mailed to each HCP, volunteer and affiliated physician. Each business entity launched educational campaigns with posters and flyers about the program Additionally, the yearly electronic infection prevention education program required for all direct caregivers includes information about the mandatory influenza vaccination program and the value of vaccination. Notices were sent to contractors, vendors and schools associated with MSH for medical, nursing, and other affiliated programs to inform them about the policy. The vendor management program, which requires vendors to comply with hospital policies, was used to manage vendor vaccination compliance. All non-employed agents were required to comply with vaccination if they did not comply, they were not allowed on MSH property."

Unlike other health systems, Medstar did not require mask usage by healthcare workers who were granted a medical or religious exemption. Karanfil, et al. (2011) note, "Although they were not required to wear masks while in patient-care areas, they received written information on the signs and symptoms of influenza. They were also strongly cautioned not to come to work if they developed illness. A decision to not require masks for exempt HCP was based on herd immunity. At the time, we had achieved a vaccination rate higher than 80 percent and felt that herd immunity would largely protect the patients from the low number of exempt HCP. For most viral respiratory diseases, the protective effect of herd immunity begins to become relevant when immunization rates reach 83 percent to 94 percent."

The results of the mandatory vaccination program speak for themselves: During the 2009-2010 influenza season, MSH achieved 99.9 percent compliance (25,544 of 25,572 healthcare workers were compliant). Of the 25,544 compliant healthcare workers, 25,188 (98.5 percent) were vaccinated, 338 (1.3 percent) were given a medical exemption, and 18 (0.07 percent) were given a religious exemption. The vaccination rate for eight MSH hospitals was 98.5 percent (22,463 of 22,813), an increase of 87 percent over the 2008 season vaccination rate of 54 percent.

While mandates are viewed as draconian by some healthcare workers and their unions, experts believe it is the only way to ensure compliance.

"Many bioethicists have debated this issue and most have erred on the side of patient protection," Karanfil says. "The most recent perspective is from Arthur Caplan of the Center for Bioethics at the University of Pennsylvania, in the Lancet. I think he said it best: 'Vaccination is a duty that one assumes in becoming a healthcare provider. Mandating vaccination is consistent with professional ethics, benefits many, including some of whom must rely on healthcare workers to protect them, maintains a stable workforce, and sets an example that permits honest engagement with others working in hospital settings and with the general public in educating them to do the right thing about vaccination. The fact that vaccination against influenza works is important in discussing mandates. The moral case for mandates when integrated with this fact can command the support of healthcare workers. It is time to acknowledge professional duty and make influenza vaccination of healthcare workers a mandatory obligation.'" Karanfil continues, "When the president and physician of the MedStar Health Research Institute sent an announcement to his staff about mandatory influenza vaccination, he reminded them about the Hippocratic oath they took as physicians: 'I will apply, for the benefit of the sick, all measures [that] are required. I will prevent disease whenever I can, for prevention is preferable to cure.'"

References:

Daugherty EL, Speck KA, Rand CS and Perl TM. Perceptions and Influence of a Hospital Influenza Vaccination Policy. Infect Control Hosp Epidem. Vol. 32, No. 5. May 2011.

Esolen LM, Kilheeney KL, Merkle RE and Bothe A. An Alternate Approach to Improving Healthcare Worker Influenza Vaccination Rates. Infect Control Hosp Epidem. Vol. 32, No. 7. July 2011.

Karanfil LV, Bahner J, Hovatter J and Thomas WL. Championing Patient Safety through Mandatory Influenza Vaccination for All Healthcare Personnel and Affiliated Physicians. Infect Control Hosp Epidem. Vol. 32, No. 4. April 2011.

Sidebar

Infectious Disease Experts Remind Healthcare Workers of the Importance of Flu Vaccination

Low influenza vaccination rates among healthcare personnel, reported by the Centers for Disease Control and Prevention (CDC), raises patient safety concerns, according to the Society for Healthcare Epidemiology of America (SHEA). Vaccination of healthcare personnel is a professional and ethical responsibility, and as a reminder of the critical importance of vaccination in preventing and controlling the spread of the flu virus, SHEA has re-issued its 2010 position paper recommending mandatory flu vaccination for all healthcare personnel.

In mid-August, the Centers for Disease Control and Prevention (CDC) released its Influenza Vaccination Recommendations for the 2011-2012 Season along with data from a study of influenza vaccination among healthcare personnel. The study, published in the Aug. 18, 2011 Morbidity and Mortality Weekly Report (MMWR) found that influenza vaccination rates among health care personnel has increased slowly over the past ten years, reaching only 63.5 percent in last years flu season. However, where vaccination was a requirement for employment, rates reached 98.1 percent, according to the study.

"As healthcare providers, we are ethically obligated to take the necessary precautions to prevent the spread of viruses such as influenza and to keeping our patients, fellow workers and ourselves safe from acquiring the virus in healthcare settings," said Steve Gordon, MD, president of SHEA. "The data from the CDCs study demonstrates the effectiveness of policies that makes vaccination a requirement for employment."

In addition to mandatory vaccination, SHEA promotes comprehensive programs designed to prevent the spread of influenza that include identification and isolation of infected patients, adherence to hand hygiene and cough etiquette, the appropriate use of protective equipment, and restriction of ill healthcare personnel and visitors in healthcare facilities.

Sidebar

ACIP Recommendations for 2011-2012 Flu Season

The Advisory Committee on Immunization Practices (ACIP) has issued its recommendations for the 2011-2012 influenza season; here are the most pertinent points to consider:

- The 2011-2012 U.S. seasonal influenza vaccine virus strains are identical to those contained in the 2010-2011 vaccine. These include A/California/7/2009 (H1N1)-like, A/Perth/16/2009 (H3N2)-like, and B/Brisbane/60/2008-like antigens. The influenza A (H1N1) vaccine virus strain is derived from a 2009 pandemic influenza A (H1N1) virus.

- Routine annual influenza vaccination is recommended for all persons aged 6 months. To permit time for production of protective antibody levels, vaccination should optimally occur before onset of influenza activity in the community, and healthcare providers should offer vaccination as soon as vaccine is available. Vaccination also should continue to be offered throughout the influenza season.

- Although influenza vaccine strains for the 2011-2012 season are unchanged from those of 2010-2011, annual vaccination is recommended even for those who received the vaccine for the previous season. Although in one study of children vaccinated against A/Hong Kong/68 (H3N2) virus, vaccine efficacy remained high against this strain 3 years later, the estimated efficacy of vaccine decreased over the seasons studied. Several studies have demonstrated that post-vaccination antibody titers decline over the course of a year, therefore annual vaccination is recommended for optimal protection against influenza.

- Children aged 6 months through 8 years require two doses of influenza vaccine (administered a minimum of four weeks apart) during their first season of vaccination to optimize immune response. Vaccination providers should note that, in previous seasons, children aged 6 months through 8 years who received only one dose of influenza vaccine in their first year of vaccination required 2 doses the following season. However, because the 2011-2012 vaccine strains are unchanged from the 2010-2011 season, children in this age group who received at least one dose of the 2010-2011 seasonal vaccine will require only 1 dose of the 2011-2012 vaccine. Children in this age group who did not receive at least 1 dose of the 2010-2011 seasonal influenza vaccine, or for whom it is not certain whether the 2010-2011 seasonal vaccine was received, should receive 2 doses of the 2011-2012 seasonal influenza vaccine.

- Multiple influenza vaccines are expected to be available during the 2011-2012 season; they include: Fluzone (Sanofi Pasteur); Fluvirin (Novartis Vaccines); Fluarix (GlaxoSmithKline); FluLaval (ID Biomedical Corp.); Afluria (CSL Biotherapies); Fluzone High-Dose (Sanofi Pasteur); Fluzone Intradermal (Sanofi Pasteur); and FluMist (MedImmune). All contain the same antigenic composition. Package inserts should be consulted for information regarding additional components of various vaccine formulations.

Reference: Prevention and Control of Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2011. MMWR. August 18, 2011.