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Background rates of serious health events in mass-vaccinated populations
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Reference: Lancet, published early online 31 October 2009
Source: Lancet
Date published: 02/11/2009 16:26
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Summary
by: Jim Glare
A review in the Lancet provides estimates for the background rates of several serious health events in a number of populations worldwide, to inform the assessment of adverse events occurring during mass vaccination campaigns for pandemic H1N1 influenza.
The authors note that awareness of background rates for serious diseases will be important for assessment of vaccine safety during mass flu vaccination campaigns, to inform the accurate assessment of vaccine safety and allow false associations to be countered. They therefore obtained data from published sources and electronic healthcare systems on background incidence rates for a list of disease events: these were selected from a wider list suggested by US and UK vaccine safety agencies on the basis of those for which relevant data could be obtained readily. Information was obtained by literature review and from a number of healthcare databases. From these data, they estimated the numbers of events that might occur 1 day, 1 week, and 6 weeks after a hypothetical vaccination.
The main conditions studied included Guillain-Barr? syndrome and related syndromes, optic neuritis (may be a presenting symptom of multiple sclerosis, MS), Bell's palsy, anaphylaxis, seizures, sudden death, and spontaneous abortion. The data show significant variations in many of the conditions studied, both between countries and within them, and with age. For example, incidence of Guillain-Barr? syndrome in Finland varied nearly 60-fold between boys under 18 and men over 64 (0.18 and 10.13 per 100,000 person-years respectively), whereas its incidence in UK men over 64 was 4.57 cases per 100,000 person-years. Data on MS from Canada showed a 2-fold variation between Alberta and Nova Scotia (19.6 to 25.0 and 10.81 per 100,000 person-years respectively).
Based on the available data, the authors estimate as examples that in the UK, for every 10 million people vaccinated, the expected number of coincidental background cases of Guillain-Barr? syndrome and sudden death* within 6 weeks of vaccination would be around 21.5 and 5.75 respectively; 3.58 and 0.98 of these would be within the first week. In the same number of US females, there would be 86.3 and 14.4 cases of optic neuritis in the same periods.
As pregnant women are likely to be targeted for vaccination because of the serious impact that H1N1 flu appears to have in this group, it was considered important to determine the background rates for spontaneous abortion. In the UK, this is documented to occur in about 12% of pregnancies, which equates to about 397 per 1 million vaccinated women within one day of vaccination (approaching 3,000 within a week and over 16,500 within 6 weeks).
The authors conclude that mass vaccination campaigns will be associated with significant numbers of coincidental serious adverse events; vaccine safety assessments will be aided by knowing what the background rates for these are in different populations. They also note that there will inevitably be clusters of cases purely by chance, and that these should not be associated with the vaccine except after careful study: as an example, they note that about 2% of UK GP practices will have apparently high rates (>2 SDs above the mean) of spontaneous abortion after any such campaign.
An accompanying Comment discusses the study and the initiatives taking place to monitor the safety of H1N1 flu vaccine.
[* Editor's note - although not clear in the text, the context indicates this to be related to adults aged under 60yr and infants aged under 5yr.]
About this library entry
Category: 14.4 Vaccines and antisera | Adverse Drug Reactions |
Abstract
Comment; link to full text (subscription required for access)
<!-- Common metadata -->
Reference: Lancet, published early online 31 October 2009
Source: Lancet
Date published: 02/11/2009 16:26
<!-- Individual metadata -->
Summary
by: Jim Glare
A review in the Lancet provides estimates for the background rates of several serious health events in a number of populations worldwide, to inform the assessment of adverse events occurring during mass vaccination campaigns for pandemic H1N1 influenza.
The authors note that awareness of background rates for serious diseases will be important for assessment of vaccine safety during mass flu vaccination campaigns, to inform the accurate assessment of vaccine safety and allow false associations to be countered. They therefore obtained data from published sources and electronic healthcare systems on background incidence rates for a list of disease events: these were selected from a wider list suggested by US and UK vaccine safety agencies on the basis of those for which relevant data could be obtained readily. Information was obtained by literature review and from a number of healthcare databases. From these data, they estimated the numbers of events that might occur 1 day, 1 week, and 6 weeks after a hypothetical vaccination.
The main conditions studied included Guillain-Barr? syndrome and related syndromes, optic neuritis (may be a presenting symptom of multiple sclerosis, MS), Bell's palsy, anaphylaxis, seizures, sudden death, and spontaneous abortion. The data show significant variations in many of the conditions studied, both between countries and within them, and with age. For example, incidence of Guillain-Barr? syndrome in Finland varied nearly 60-fold between boys under 18 and men over 64 (0.18 and 10.13 per 100,000 person-years respectively), whereas its incidence in UK men over 64 was 4.57 cases per 100,000 person-years. Data on MS from Canada showed a 2-fold variation between Alberta and Nova Scotia (19.6 to 25.0 and 10.81 per 100,000 person-years respectively).
Based on the available data, the authors estimate as examples that in the UK, for every 10 million people vaccinated, the expected number of coincidental background cases of Guillain-Barr? syndrome and sudden death* within 6 weeks of vaccination would be around 21.5 and 5.75 respectively; 3.58 and 0.98 of these would be within the first week. In the same number of US females, there would be 86.3 and 14.4 cases of optic neuritis in the same periods.
As pregnant women are likely to be targeted for vaccination because of the serious impact that H1N1 flu appears to have in this group, it was considered important to determine the background rates for spontaneous abortion. In the UK, this is documented to occur in about 12% of pregnancies, which equates to about 397 per 1 million vaccinated women within one day of vaccination (approaching 3,000 within a week and over 16,500 within 6 weeks).
The authors conclude that mass vaccination campaigns will be associated with significant numbers of coincidental serious adverse events; vaccine safety assessments will be aided by knowing what the background rates for these are in different populations. They also note that there will inevitably be clusters of cases purely by chance, and that these should not be associated with the vaccine except after careful study: as an example, they note that about 2% of UK GP practices will have apparently high rates (>2 SDs above the mean) of spontaneous abortion after any such campaign.
An accompanying Comment discusses the study and the initiatives taking place to monitor the safety of H1N1 flu vaccine.
[* Editor's note - although not clear in the text, the context indicates this to be related to adults aged under 60yr and infants aged under 5yr.]
About this library entry
Category: 14.4 Vaccines and antisera | Adverse Drug Reactions |
Abstract
Comment; link to full text (subscription required for access)
