By Jenifer Leaf Jaeger, MD, MPH, Interim Medical Director, Boston Public Health Commission

The Public Health Impact of Influenza
While seasonal influenza (flu) viruses are detected year-round in the United States, flu activity begins to rise above baseline in the Northeast in October, with “peak season” extending December through March. The Centers for Disease Control and Prevention (CDC) monitors several flu indicators, including outpatient visits for influenza-like illness, results of laboratory testing, and reports of flu-related hospitalizations and deaths. Flu season is defined by the persistent elevation of these indicators.

According to CDC, influenza resulted in an annual 9.2 to 35.6 million influenza illnesses in the United States between 2010-2016, including: 4.3 to 16.7 million influenza-related medical visits; 140,000 to 710,000 influenza-related hospitalizations (including ~20,000 children <5 years of age); and 12,000 to 56,000 pneumonia/influenza deaths (including 37 to 171 deaths among children <5). The rate for respiratory/circulatory deaths related to influenza is estimated to be 2-4 times greater. WHO estimates the worldwide incidence of severe influenza illness at three to five million cases, resulting in 300,000-500,000 deaths annually.

The estimated annual economic burden of seasonal influenza in the U.S. reached $34.7 billion in direct medical and indirect costs associated with lost earnings and productivity, and lost lives. Annual flu vaccine is estimated to prevent 5.1 million influenza illnesses, 2.5 million medical visits, 71,000 hospitalizations, and 3,000 pneumonia/influenza deaths.

As we face one the worst flu season in nearly a decade, it is important for local health departments to continue engaging in critical preparedness and response activities that help to mitigate the flu and flu-related complication.

The Role of Public Health Surveillance
The predictable, cyclical pattern of influenza allows for effective preparedness and prevention efforts. Surveillance approaches include traditional and more innovative strategies. Ongoing baseline surveillance allows for improved situational awareness and improved clinical care with early targeted education and outreach efforts. Population level surveillance identifies disparities promoting health equity in prevention, diagnosis, and treatment practices. For example, FluView, CDC’s weekly U.S. influenza surveillance report, provides a synopsis of flu activity and trends of laboratory-confirmed influenza, virus characterization, geographic spread of influenza-like illness (ILI), and illness severity including hospitalizations, pneumonia, and death. Local trends may not reflect trends reported for the State or Country which average across a disperse area where testing and reporting practices vary greatly.

Understanding Vaccine Effectiveness
Vaccine effectiveness (VE) is impacted by factors such as age, overall health status, and the similarity or “match” between the flu viruses the vaccine is designed to protect against and the flu viruses spreading in the community. In contrast to standard childhood vaccines, for which efficacy rates range between 92.2-100%, flu VE is substantively lower – even when the vaccine is a “good antigenic match.” Efficacy also varies by influenza type: on average, the efficacy for influenza A(H3N2) is 33% (~23% when vaccine is a “poor match”); efficacy for influenza A(H1N1) is 61%; and for influenza B, viruses average 54%. VE tends to be poor for influenza A(H3N2) viruses due to the increased rate of antigenic change of these viruses, particularly during growth in eggs (as employed for vaccine manufacturing and production), called egg-adaptation. During the 2016-2017 flu season, the overall VE for the flu vaccine was 39% and for the A(H3N2) component, which is the same circulating strain as the current year, effectiveness was 32%.

Among circulating wild-type influenza viruses, including H3N2, no significant antigenic drift has been identified; the majority of H3N2 viruses collected and tested by the CDC since October 1, 2017 are similar to the egg-grown reference virus representing the virus recommended for use in the majority of Northern hemisphere vaccines. During the 2014-15 season, the vaccine was considered a “bad match” with nearly 80% of circulating A(H3N3) virus differing from vaccine virus.

Concern was raised early in the 2017-2018 flu season in response to learning that the 2016-2017 Australian flu vaccine demonstrated an overall VE of just 10% versus the A(H3N2) component. The current 2017-2018 vaccine in use in the U.S. contains the same A(H3N2) virus strain, however numerous conditions make direct comparison of VE between the Northern and Southern hemispheres inapplicable.

Providers should continue offering vaccine to all persons 6 months of age and older through the remainder of the season. While it is still possible for individuals who have been vaccinated to get the flu – though not from the vaccine itself – studies have shown that prior vaccination during the season can attenuate the severity of illness, reduce the risk of flu-associated hospitalization, and result in fewer influenza-associated deaths particularly for children, pregnant women, and persons with chronic health conditions. Vaccination is the best way to prevent influenza and its complications and protect those around you, including those more vulnerable to serious flu illness.

Boston Public Health Commission: Multi-Pronged Approach

Boston Public Health Commission (BPHC) has a robust surveillance system collecting flu data from multiple streams including case reporting, social media, and syndromic surveillance collected from 12 acute care sites throughout Boston, as well as extensive historical data against which to compare the current year. Healthcare providers and laboratories in Boston are required by city health department regulations to report all laboratory-confirmed cases of influenza, along with clusters of illness, to the Infectious Disease Bureau (IDB) at BPHC.

Communicating with Healthcare Partners and the Community
During the influenza season, BPHC electronically sends a weekly Influenza Report to healthcare providers (HCPs), emergency departments (ED), emergency preparedness, and other external stakeholders from its Medical Intelligence Center. This report includes epidemiologic data and trends-by-week, summarized from the beginning of the season; a total count of reported cases of influenza A and B; and influenza-like illness as percent of total ED cases seen to-date. Lab-confirmed cases of influenza are analyzed by age, race/ethnicity, and neighborhood. Weekly counts are compared to the previous two influenza seasons, and weekly reports are posted on the BPHC website. At the end of the influenza season, data are analyzed to identify trends and areas of concern. With this information, BPHC sends out Flu in Review prior to the beginning of the following flu season, to highlight trends from the previous year and provide recommendations for what HCPs should prepare for in the coming season.

Flu Vaccination Tracking at BPHC
The Massachusetts Hospital Association, member hospitals and health systems, and the Massachusetts Department of Public Health (MDPH) all support mandatory flu vaccination for all HCPs. Although not required by Massachusetts law, as of the 2017-2018 flu season, HCPs are strongly encouraged to receive flu vaccine by MDPH, which established a minimum performance goal of 90% for all licensed facility HCPs at hospitals, Community Health Centers, and Long-Term Care Facilities.

At BPHC, all non-union employees are required by contract to be vaccinated against seasonal influenza. Further, through contract negotiation, 8 of 9 union contracts contain language requiring employees to be vaccinated unless their program director determines this unnecessary due to lack of client contact. BPHC provides flu vaccine clinics to employees. Employees not providing documentation of vaccine are prohibited from work. Of those BPHC employees not exempt or on leave (70% of all employees), 100% received flu vaccine during the 2017-2018 season.

To access additional information about Boston’s public health efforts to increase influenza awareness, visit the Boston Public Health Commission’s Flu Information Center. And for more information on fighting flu at the local level, check out these resources for local health departments.