Challenges in adult vaccination

Figures & data

Table

In contrast to younger individuals, hematopoietic stem cells (HSCs) in older subjects show a greater differentiation into myeloid progenitors at the expense of lymphoid progenitors than in younger individuals [5]. This results in fewer circulating antigen presenting cells (APCs) and a relative shift in the proportions of naïve and memory cells within both B and T-cell populations (fewer naïve cells and a corresponding increase in memory T and B cells) [5,6]. As a result, overall antibody production and specificity is diminished. It is this shift which leads to impaired immunity against infection in older people, and also to reduced vaccine efficacy and shorter duration of vaccine response [5]. A general increase in pro-inflammatory cytokine levels is also seen (in particular IL-6 and TNF-α), secreted by aging HSCs, and by other tissue cells as part of a more generalized cellular senescence [4,5].

*It is important to realize that substantial variation exists in the relative contribution and extent of these mechanisms in individuals, and no direct correlation with specific chronological ages can be made.

Table 1. Adult vaccine coverage in the Unites States in 2015 (NHIS) [25].

Vaccine	Vaccine coverage (%)
	All	By age group (years)								HCWs
	≥19	19–64	19–26	19–49	50–64	≥50	≥60	60–64	≥65	All	Direct care^a
Hepatitis A^b	9.0			12.3		5.5
Hepatitis B^c	24.6			32.0		16.5				64.7	74.1
HPV^d
Females			41.6
Males			10.1
Influenza^e	44.8			32.5	48.7				73.5	68.6	68.9
Pneumococcal^f		23^g							63.6
Tetanus (alone)^h	61.6			62.1	64.1				56.9
Tdap^h	23.1	24.7							16.5	45.6	51.1
Herpes zoster^i							30.6	21.7	34.2

^a HCWs with direct patient responsibilities.

^b Reported receipt of at least two doses of hepatitis A vaccine (ever).

^c Reported receipt of at least three doses of hepatitis B vaccine (ever).

^d Reported receipt of at least one dose of HPV vaccine (ever).

^e For the previous 2014–2015 season.

^f Reported receipt at least one dose of pneumococcal vaccine (ever).

^g Adults aged 19–64 years at increased risk of pneumococcal disease.

^h Within past 10 years.

ⁱ Reported receipt of herpes zoster vaccine (ever).

Tdap: tetanus, diphtheria and pertussis vaccine; HCW: health care worker; NHIS: National Health Interview Survey.

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