Poliovirus‐Specific Memory Immunity in Seronegative Elderly People Does Not Protect against Virus Excretion
1Department of Infectious Disease Epidemiology, 2Laboratory for Vaccine‐Preventable Diseases, and 3Computerization and Methodological Consultancy Unit, National Institute of Public Health and the Environment, Bilthoven, and 4Rivierenland Municipal Health Services, Tiel, The Netherlands
Background.
Dutch people born between 1925 and 1945 were ineligible for vaccination with the inactivated poliovirus vaccine (IPV) introduced in 1957 and may have escaped natural infection because of reduced poliovirus circulation. We examined whether people with low or undetectable antibody levels are susceptible to infection and whether memory immunity provides protection against virus excretion.
Methods.A total of 429 elderly participants were challenged with monovalent oral poliovirus vaccine (type 1 or 3) and followed for 8 weeks. Immune responses and virus excretion were compared for 4 groups, defined on the basis of seronegativity for poliovirus type 1 or 3, natural immunity, and IPV‐induced immunity.
Results.On the basis of the rapidity of the antibody response and the absence of immunoglobulin M, we saw clear evidence of memory immune responses in 33% of the participants without detectable antibodies against poliovirus type 1 and in 5% of the participants without detectable antibodies against poliovirus type 3. Fecal virus‐excretion patterns were not significantly different for seronegative participants, regardless of whether they showed evidence of memory immunity.
Conclusions.Rapid antibody responses after challenge with oral polio vaccine provide evidence for poliovirus‐specific memory immunity in seronegative elderly people. However, in contrast to preexisting immunity, memory immunity does not protect against virus excretion. These results have important implications for the poliomyelitis‐eradication initiative, in particular for future immunization policies after eradication has been achieved.
Received 20 January 2004; accepted 19 August 2004; electronically published 10 February 2005.
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Online publication date: 1-Mar-2008.
Online publication date: 1-Jan-2007.
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Presented in part: 13th European Congress of Clinical Microbiology and Infectious Diseases, Glasgow, United Kingdom, 10–13 May 2003 (abstract P683).
Financial support: Health Research and Development Council (ZonMw), The Netherlands.