Immunosenescence, the gradual deterioration of the immune system due to aging, is a key reason why older adults suffer a disproportionate burden of influenza each season. The declining immune system is also why older adults typically mount a less robust response to vaccination, although they would benefit greatly from vaccine-induced immunity. Recent advances in vaccine technology have led to the availability of two influenza vaccines designed specifically for adults age 65 years and older.
While it is optimal to administer influenza vaccines earlier in the season, vaccination continues to be valuable and recommended throughout the influenza season while viruses are still circulating. In the U.S., influenza season can begin as early as October and last as late as May. Now is a good time to learn more about the new vaccines, review the burden of influenza on older adults, and seek or recommend annual influenza vaccination.
Adjuvanted influenza vaccine
Adjuvanted influenza vaccine was first approved for U.S. adults age 65 years and older for the current 2016-2017 influenza season; it has been used in Italy since the 1990s and is licensed in 38 other countries. Vaccine safety has been confirmed in clinical and observational studies including approximately 120,000 subjects, and by 2013 more than 60 million doses had been distributed for use in older adults worldwide. The vaccine was approved based on immunogenicity data showing that compared to standard-dose vaccine in adults age 65 years and older, adjuvanted influenza vaccine elicited higher antibody responses for influenza A (H1N1), influenza A (H3N2), and influenza B. The vaccine met superiority criteria set by the U.S. Food and Drug Administration for the A (H3N2) strain, which causes the most severe disease across all age groups. Prospective, randomized efficacy trials for this vaccine have not yet been reported.
High-dose influenza vaccine
High-dose influenza vaccine contains four times more antigen than standard-dose vaccine. With more than 50 million doses distributed in the U.S. since its introduction in 2009, the safety of high-dose vaccine is well established. Like the adjuvanted vaccine, the high-dose vaccine was approved for adults age 65 years and older based on immunogenicity data. High-dose influenza vaccine elicited significantly higher antibody responses compared with standard-dose vaccine for all three influenza strains (influenza A [H1N1], influenza A [H3N2], and influenza B). Post-licensure trials have confirmed clinical efficacy of the high-dose vaccine. Relative to standard-dose vaccine in adults 65 and older, high-dose vaccine reduces the risk of laboratory-confirmed influenza by 24%, all-cause hospitalization by 7%, cardiorespiratory events potentially related to influenza by 18%, and pneumonia by 40%.
The impact of flu in older adults goes beyond respiratory complications
Common influenza symptoms are relatively well known: sudden onset of high fever, muscle and body aches, chills, and extreme tiredness, as well as sore throat and runny or stuffy nose. But in older adults, the same changes in the immune system that lead to worse outcomes and challenge vaccine response may also affect the clinical presentation of the illness, potentially leading to misdiagnosis. The sudden onset of fever common in children and younger adults may be replaced by malaise in older adults, in whom gastrointestinal symptoms including pain, diarrhea, nausea, and vomiting are also more frequent.
Unfortunately, the outcomes of influenza in the 65 and older population are markedly worse than for any other age group. In addition to the well-known risks of death (six times more than all other age groups combined) and hospitalization, influenza also increases the risk of heart attack and stroke.
Older adults experience a slower systemic inflammatory response, accounting for the difference in the acute presentation of influenza, but the inflammation lasts longer. Acute inflammation helps the body mount an immune response, but chronic inflammation is associated with increased risk of heart disease, cancer, and other serious illnesses.
In adults,, age 65 years and older, influenza and pneumonia can raise the risk of heart attack by three to five times and of stroke by two to three times in the first two weeks of infection. Alarmingly, these risks can remain elevated by about one-third for up to three months.
New vaccine technology may help reduce other respiratory virus related illnesses
There are many winter respiratory viruses that infect people of all ages annually. Currently, influenza is the only one for which there is a vaccine available. Following decades of research, progress is being made in the development of vaccines against respiratory syncytial virus (RSV).
Like influenza, RSV hits older adults particularly hard. In the U.S., RSV causes an estimated 2.6 million cases in adults age 65 years and older annually, hospitalizing 177,000 and killing 14,000. While the annual attack rate and severity of influenza vary, RSV is marked by its consistency year to year. RSV symptoms can be very similar to the flu, especially in older adults. The similar clinical presentation coupled with little availability of point-of-care testing have helped to mask and underestimate the true impact of RSV.
With the potential for RSV vaccines and specific treatments in the future, the importance of increased awareness about the annual impact of RSV, particularly in older, more vulnerable adults cannot be understated.
The National Foundation for Infectious Diseases (NFID) recently held an expert roundtable to discuss the challenge of increasing stagnant influenza vaccination rates in the 65 and older population and the role of vaccines targeted specifically for older adults. The NFID Call to Action, Reinvigorating Influenza Prevention in U.S. Adults Age 65 Years and Older, further details potential solutions.
NFID also published a report, Respiratory Syncytial Virus in Older Adults: A Hidden Annual Epidemic, focused on the impact of respiratory syncytial virus in older adults and the challenges associated with diagnosis and treatment.
It is important to build awareness among the public and healthcare professionals about the need to protect older adults from influenza and RSV infections. We all must continue to work collaboratively to remove any barriers to disease prevention.