HERD PROTECTION BY IMMUNIZATION. W. Paul Glezen, M.D. Herd Protection against Influenza. “…it is apparent that progress in the control of influenza has not been impressive. A reassessment of the basic assumptions upon which the program was developed is warranted.”.
W. Paul Glezen, M.D.
“…it is apparent that progress in the control of influenza has not been impressive.
A reassessment of the basic assumptions upon which the program was developed is warranted.”
A. D. Langmuir et al 1964; Am J Public Health 54:563-71
Universal Recommendations Generally Are More Successful
e.g.: > 65 yr, 6-23 mo., Ontario program
The most vulnerable persons – elderly and infants – have poor immune responses to vaccines and are at the end of the transmission chain = inefficient use of vaccine.
Immunization of these groups has the potential for establishing indirect protection of the vulnerable [HERD IMMUNITY or HERD PROTECTION] = efficient use of influenza vaccine.
Rate Per 1000 Persons
Ghendon et al. Epidemiol. Infect 2006;134:71-8.
# children #vaccinated %efficacy
Kindergarten 6,374 3,659 (57.4%) 60.9
School aged 34,237 24,651 (72%) 68.8
Total 40,611 26,275 (64.7%) 63.7
Indirect (herd) protection
Achieved with only 28,310 vaccine doses – sufficient for 34.5% of 82,051 persons > 60 years of age.
Ghendon et al. Epidemiol Infect 2006;134:71-8.
Reichert et al. N Engl JMed 2001;344:889
For Direct Effectiveness of LAIV in 2003-2004, see Piedra, et al.
Abstract # 726
Piedra et al: Vaccine 2005;23:1540-8
Piedra et al: Live attenuated intranasal influenza vaccine-trivalent (LAIV-T) administered during the 2003-04 influenza type A(H3N2) outbreak provided immediate, direct and indirect protection in children. PEDIATRICS 2007, in press.
Never vaccinated 127/231(55%) reference
LAIV-T* 19/55(34.5%) 37.3% 0.006
TIV* 14/24(58.3%) 0% NS
*LAIV-t = live attenuated influenza vaccine, TIV = inactivated influenza vaccine
Vaccine status No.+/No. cultured (%) Efficacy p-value
LAIV-T 10/25(40.0) 4/14(28.6) 5/16(31.3)
TIV 7/9(77.8) 7/15(46.7)
Vaccine No. positive/no. cultured (%) by 2-week periods
1-2 3-4 >4
2004-2005 Epidemic Caused by Influenza A/California (H3N2) with ~30% Vaccinated with A/Fujian (H3N2) Vaccine.
2005-2006 Epidemic With Emergence of Another New H3N2 Variant, A/Wisconsin (H3N2), plus Influenza B, with ~5,309 received LAIV and 1,904 received TIV containing A/California (H3N2) and B Shanghai/361/2002 (Yamagata lineage) antigens. B outbreak due to B/Ohio, Victoria lineage.
Relative risk of MAARI for Intervention/Comparison Sites at Specified Intervals
RR: 0.99 1.00 0.90 1.04
95%CI 0.91,1.07 0.93,1.08 0.84,0.96 0.97,1.11
Pre-epidemic Vaccine delivery Epidemic Post-Epi
RR: 1.04 1.02 0.89 1.06
95%CI 0.99,1.09 0.98,1.07 0.85,0.921.02,1.10
Direct and Indirect Effectiveness of the School-Aged Influenza Vaccine Program during the Influenza B Outbreak, 2005-06, Piedra et al: Pediatric Academic Societies Annual Meeting, May 8, 2007.
Relative Risk (RR) for MAARI by Age Group (yr)
<5 5-17 18-34 >35
Pre-epidemic 1.131.20 1.06 1.07
Epidemic 0.96 0.88 0.95 0.94
Underline = significant (95%CI did not cross 1.0)
1. Current ACIP recommendations give influenza immunization priority to 218 million people (72.7% of US population) including:
a. children 6 – 59 months,
b. adults > 50 years,
c. high risk 5 – 49 years of age
d. pregnant women
e. health care workers, caretakers
f. household contacts of children < 5 years and all high risk
2. The infrastructure does not exist to accomplish this.
3. A practical complementary strategy is to utilize school-based and workplace-based clinics to systematically immunize all school children and working adults annually.
4. This would provide time to access elderly and high risk.
5. Viral surveillance must be improved to facilitate efficient use of antivirals.
6. Effective interpandemic control will increase demand for vaccines and antivirals to assure supplies and establish infrastructure for effective utilization of both during the pandemic.