Vaccination In The Elderly
The College of Family Physicians organised a 2 day seminar entitled “Vaccinations in Adults” on May 26th and 27th 2018. Dr Wong Sin Yew was invited to speak on “Vaccinations in the Elderly” and this is an excerpt of his talk and also a summary of Dr Wong and Dr Loh Jiashen’s article in the May 2018 issue of the Singapore Family Physician.
With improvements in health care globally, the proportion of elderly will increase markedly. For persons aged 60 years and above, it is estimated that the numbers will double to 2.1 billion in 2050. For those aged >80 years, it is expected to increase from 125 million in 2015 to 434 million in 2050. In Singapore, a quarter of the population will be aged >65 years by 2030. It is important to highlight the following:
- The elderly population will be more susceptible to infections because of waning immunity
- The elderly have a poorer response to infection and often have underlying disabilities (physical and functional) and co-morbidities. They often have a suboptimal response to vaccines as well
- Infections in the elderly are often more severe and many of these infections are associated with long term sequelae including physical de-conditioning, impairment of activities of daily living and loss of independence
Vaccination is the most effective means to prevent infection. There has been a greater appreciation that vaccinations should continue throughout life. The professional medical societies including College of Family Physicians, the Chapter of Infectious Disease Physicians and Society of Infectious Diseases have published Clinical Practice Guidelines on Adult Vaccination in Singapore in 2016. The Ministry of Health, Singapore subsequently announced an adult immunisation schedule in October 2017 for which Medisave may be utilised for these vaccinations.
For the elderly (defined as >65 years of age), guidelines in Singapore and most developed countries focus on 3 types of vaccinations.
- Annual influenza (quadrivalent) vaccine which covers 2 influenza A and 2 influenza B strains
- Pneumococcal Vaccination: 2 doses with the initial vaccine as 13 valent Pneumococcal conjugated vaccine (PCV13) followed 12 months later with a 23 valent Pneumococcal Polysaccharide vaccine (PPV23)
- Herpes Zoster (HZ) Vaccination: Single dose of live attenuated HZ vaccine (Zostavax) or 2 doses of HZ subunit adjuvanted vaccine (Shingrix).
The details of these infections and vaccines are covered elsewhere on this website. Dr Wong went on to elaborate on the following:
Immunosenescence
Old age typically represents a scenario of exhaustion of reserves in our bodies. The aging phenotype is thought to be the result of an imbalance of pro-inflammatory versus anti-inflammatory mechanisms. Immunosenescence is a relatively new concept and refers to age related changes in the innate and adaptive immune system that results in remodelling of the immune system.
Successful vaccination requires the phagocytosis of vaccine and antigen presentation to naïve T cell and B cells, so that memory T and B cells may be formed. In old age, each step of this process is diminished and weakened. Neutrophils and antigen-presenting cells have impaired phagocytic capabilities. Chronic persistent increased pro-inflammatory cytokines in old age dampen the host’s ability to recognize vaccine targets as danger signals that are required to induce immunity. Many studies have demonstrated that the elderly do not produce as good an immune response to vaccinations as younger adults. Consequently, alteration in the administration of some component of the vaccine may be needed to overcome this effect.
New Vaccines For The Elderly
Our current vaccines against influenza and pneumococcal disease have limitations because they are strain specific. The focus of research has been in developing “universal” influenza and pneumococcal vaccines that provide broad spectrum and long lasting efficacy. The most attractive target currently for a universal influenza vaccine is the conserved stalk region of the haemagglutinin molecule. The remaining challenge is to find an immunogen to induce sufficient protective antibodies in humans. This effort must not only identify suitable target molecules for vaccination, but must also overcome the challenge of immunosenescence. The use of an adjuvant in HZ subunit vaccine and higher doses of antigens in high-dose influenza vaccines have been 2 successful approaches against immunosenescence. Researchers have used adjuvants for decades. One of the first adjuvants was the use of aluminium salts and it is still used as a base. The actual mechanism of its action remains unclear but it well known that aluminium may enhance antibody production but it cannot elicit immune responses against intracellular organisms. Many modern adjuvants contain more than one immune stimulatory molecule. Toll like receptor (TLR) agonists are increasingly used as adjuvants in vaccines.
Other strategies like heterologous prime-boost vaccination could also play a role to increase the low vaccine efficacy seen in the elderly. The idea behind heterologous prime-boost is to use the same vaccine antigen delivered in 2 different ways in an attempt to induce a more robust immune response.
New intra-dermal delivery methods also hold promise. The potential advantage is to make use of the abundant potent antigen-presenting dendritic cells in the skin to augment the immune response.
Conclusion
Successful aging is the concept of preserving function as long as possible in old age, hence resulting in a shortened number of disease years before demise. Vaccines remain a cornerstone in the prevention of many infectious diseases in old age. The development of improved vaccines should be coupled with effective implementation strategies for the administration of vaccines to the elderly. These strategies include raising awareness amongst prescribers, improving accessibility of vaccines to primary care centres and appropriate subsidies for the socially disadvantaged.