Measles Elimination in NZ. Dr Tom Kiedrzynski Principal Adviser, Communicable diseases, Ministry of Health

Transcription

1 Measles Elimination in NZ Dr Tom Kiedrzynski Principal Adviser, Communicable diseases, Ministry of Health

2 Presentation Outline International background WHO requirements Overview of the measles situation in NZ: Epidemiology, incl. genotyping Quality of surveillance and laboratory testing Immunisation coverage Summary of recent work measles risk analysis modelling of measles epidemics cost analysis of measles outbreaks and benefit-cost analysis of measles immunisation catch-up Conclusion What s next?

3 WHO requirements What does measles elimination mean? Absence of endemic measles virus transmission in a defined geographical area (e.g. region or country) for 12 months in the presence of a wellperforming surveillance system.

4 WHO requirements (2) Three criteria, supported by five lines of evidence for the verification of measles elimination Criteria Documentation of the interruption of endemic measles virus transmission for a period of at least 36 months from the last known endemic case; In the presence of verification-standard surveillance; and Genotyping evidence that supports the interruption of endemic transmission

5 WHO requirements (3) Lines of evidence 1. A detailed description of the epidemiology of measles since the introduction of measles vaccine in the NIP 2. Quality of epidemiological and laboratory surveillance systems 3. Population immunity presented as a birth cohort analysis with the additional of evidence related to any marginalized and migrant groups 4. Sustainability of the National Immunization Programme including resources for SIAs, where appropriate, in order to sustain elimination 5. Genotyping evidence that supports interruption of measles virus transmission

6 Epidemiology Overview of the measles situation in NZ

7 Number of notifications Rate per 100,000 population Number of measles notifications and rate per 100,000 population in NZ by year, Notifications Rate [ESR] Report year 1 The 2015 rate is annualised based on cases reported between 1 January and 30 June 2015

8 Weekly number of probable and confirmed cases, Auckland, [ARPHS]

9 Re-establishment of endemic transmission: occurs when epidemiological evidence, supported wherever possible by laboratory evidence, indicates the presence of a chain of transmission of a virus strain that continues uninterrupted for 12 months in a defined geographical area (region or country) where measles was previously eliminated.

10 Number of notifications Number of measles notifications in NZ by public health service and surveillance week, December 2013 to June Auckland Regional Public Health Service Community and Public Health Hawke's Bay Public Health Unit MidCentral Public Health Service Northland Public Health Service Population Health Service Waikato Regional Public Health Tairawhiti DHB Taranaki Health Protection Unit Toi Te Ora - Public Health [ESR] Year (surveillance week)

11 < < Number of notifications Number and classification of measles notification in NZ by age group, 2014 and January June 2015 Laboratory-confirmed Epidemiologically-confirmed [ESR] Year (by age group in years)

12 Numbers and age of measles cases in years in NZ for two periods, and [Massey University]

13 Number of notifications Number of measles notifications by outbreak and month, NZ, December 2013 to June Outbreak number [ESR] Year (by month)

14 List of outbreaks by genotype, NZ, Jan 2013 to Jun 2015 Year Outbreak Genotype B3 (Philippines) B3 with 1 base pair difference from B3 (Philippines) D8 Unknown y 2 Y y 4 y 5 y 6 y 7 y 8 y 9 y 10 y 11 y 12 y 13 y 14 y 15 y 16 y 17 y 18 y 19 y 2 20 y y 22 y 1 Index case came from the Philippines. 2 Contact with case from previous outbreak (B3 with 1 base pair difference from B3 (Philippines)) Note: all the outbreaks listed are with local transmission. [ESR]

15 Quality of surveillance Overview of the measles situation in NZ

16 WHO indicators and targets for epidemiological surveillance quality of measles notifications in NZ, 2014 and 2015 Indicator Target Proportion of surveillance units reporting measles data to 80% 100% 100% the national level on time Reporting rate of discarded non-measles non-rubella cases at the national level 2 per 100,000 population Proportion of 2 nd administrative level units reporting at 80% of 2 nd level 95% 2 85% 2 least 2 discarded non-measles non-rubella cases per administrative units 100,000 Proportion of suspected cases with adequate specimen 80% 96% 94% collection 3 Proportion of laboratory-confirmed chains of transmission 80% 85% 100% (defined as 2 or more confirmed measles cases) with specimens adequate for detecting measles virus collected and tested in an accredited laboratory 12.0 per 100, per 100,000 Proportion of all suspected measles cases that have had an adequate investigation initiated within 48 hours of notification 80% of suspected cases Data not available. Each notified case is considered to be under investigation until a further classification. All relevant clinical and demographic information on the suspected case is expected to be collected within one working day whenever possible. It is envisaged to have data on this indicator systematically collected in the future. [ESR] figures presented are annualised figures based on cases reported between 1 January and 30 June See next Table for the cases and rates by district health board (2 nd level administrative unit). 3 This indicator has been calculated using the following data: proportion of all notified measles and rubella cases (including discarded cases) that were not epidemiologically-linked to a measles or rubella case and that were laboratory-tested.

17 Immunisation (MMR) coverage Overview of the measles situation in NZ

18 MMR coverage by birth cohort and dose (2006 to 2012) as on Aug 2014 Birth cohort Number of children 62,883 66,071 66,289 65,473 65,690 62,662 62,628 MMR 1 coverage 92.6% 93.2% 93.9% 94.5% 94.6% 94.6% 93.9% MMR 2 coverage 89.8% 89.5% 88.5% N/A N/A N/A N/A N/A: not available [MoH]

19 Number of DHBs by coverage band for MMR dose one (2006 to 2012 birth cohorts), NZ, Aug 2014 Coverage band (%) Birth cohort Number of DHBs by coverage band for MMR dose two (2006 to 2008 birth cohorts), NZ, Aug 2014 [MoH] Coverage band (%) Birth cohort

20 Measles Risk Analysis Modelling of measles epidemics Cost analysis of measles outbreaks and Benefit-cost analysis of measles immunisation catch-up Summary

21 Risk Analysis Summary (1) Risk of measles infection decreases significantly with age, though a peak of cases appears again in the age class. Pacific people 0-2 year olds are statistically more at risk per capita of measles infection. There is statistical support for 2-24 year old Pacific people and 5-17 year old Asian children being less at risk than European and Maori of the same age. There is some statistical support for those living in better socio-economic situations being at greater risk of measles.

22 Risk Analysis Summary (2) The majority of vaccinated cases occur in those people which received single vaccinations around 1 year old. There is a continued, and perhaps increasing, risk of measles importation due to travel and endemic measles elsewhere in the world. There may be seasonal changes in risk of measles importation, with travel numbers peaking in December and lowest in May/June.

23 Vaccination coverage ( years) and serosurvey estimates of immunity (< 2006 birth cohorts) among different age classes [MoH] Note Values are from NIR, VPD serosurvey , and estimates based on published information. Vaccine effectiveness used for 0-4 year olds was 96%, 5-13 year olds 99%, and for 14 year olds equivocal serological results were considered non-immune. 28% of those < 1 were considered immune due to passive immunity

24 NZ population by year of birth and estimated numbers of naive people in each age class using national immunity data (top) and the number of measles cases by year of birth from (bottom)

25 Measles Epidemics Modelling Summary Regular importations of measles pose an ongoing threat to NZ s efforts to eliminate measles. The reproduction number for measles in the partially immune NZ population (Rv) is often close to and exceeding 1, suggesting increased population level immunity is required to ensure prevention of measles persistence following importation. The proportion of the currently naive population requiring additional and effective vaccination in NZ in order to push Rv below one ranges from 12% to 30% among DHBs, and is at least 24% at the national level (approximately 104,357 vaccinations).

26 Measles Epidemics Modelling Summary (2) After vaccination to ensure Rv is < 1 Measles introductions to New Zealand with a median outbreak size of 2 cases were predicted by simulation models Thus, typically individual cases would be expected on average to infect a single secondary cases. However, the mean outbreak size of 61 cases was predicted, because of larger outbreak sizes predicted among 1000 simulations following importation, despite Rv being one and the outbreak predicted to die out.

27 Measles Epidemics Modelling Summary (3) Thus, increased vaccination beyond the 24% of the currently 10% naive population required may be useful to prevent these rare but costly events. WHO advice is 95 % of the population immunised with MMR2.

28 Measles Outbreaks Cost Analysis Summary The cost of the first 187 measles cases in 2014 is estimated to be approximately $1,041,186 due to earnings lost for cases and contacts, case management and hospitalisation costs. The mean wage loss per measles case is estimated to be approximately $839. The mean cost of those measles cases that attend hospital is estimated to be $1,877 per attending case. Approximately 17% of measles cases attend hospital. The mean public health service cost per case is $1,765. The average number of contacts per case requiring quarantine was 2.11, requiring 7.3 days of quarantine on average, at a cost of $170 per day.

29 Measles Immunisation Catch-Up Benefit-Cost Analysis Summary The benefit-cost (B/C) ratio analyses suggest additional vaccination is beneficial financially (B/C >1), with vaccination-related costs required to exceed approximately $74 per person currently naive immunized through vaccination before the costs exceed the benefits for all DHBs together if the outbreaks continue with an average number of annual cases based on figures. However, in a scenario without PH intervention, or with larger continuing outbreaks, vaccination-related costs are required to exceed approximately $3000 per person currently naive immunized through vaccination before exceeding the benefits. The B/C ratio differed across DHBs with those with large populations and more naive in absolute numbers most likely to benefit from immunisation campaigns.

30 Measles Immunisation Catch-Up Benefit-Cost Analysis Summary (3) This analysis doesn t take into account the benefits related to the rubella and mumps vaccine component of MMR

31 Conclusion Good news!! NZ will request the verification of measles elimination in Report being written NVC yet to be organised Bad news... However, NZ is at risk of further significant measles outbreaks and of reestablishment of endemic transmission Huge improvements in coverage since 2006 MMR2 immunisation coverage is still significantly under 95% Older population groups are less immunised Overall population immunity is likely around 90% only Outbreaks since 2009 All recent significant outbreaks affected school-age children Schools also offer a particularly good environment for measles transmission. Risk for non-immunised students: disease and restriction (exclusion) As part of the WPRO RCM, NZ has agreed to eliminate measles SIA are expected to be part of the sustainability of the programme Benefit-cost of MMR immunisation catch up for measles is clear

32 What s next? What is required? A catch-up campaign or SIA Further coverage improvements is specific population groups and geographical areas Aim at 95% coverage by MMR2 Catch-up campaign Should reach about 50% of those non-immunised Proposed main target = school aged children born before the introduction of NIR, students, and young adults up to the age of 30 years without 2 MMR documented Plus possibly anybody else born after 1968 without 2 MMR documented All DHBs, starting with Auckland region and the other big PH regions MoH to share current information and communicate with PHOs, DHBs and PHUs Key questions How to identify those not immune? Evaluation? Funding?

33 Acknowledgements Environmental Science and Research Institute (ESR) Surveillance information Massey University Additional risk analysis, modelling, cost and benefit/cost analysis MoH - MMR Coverage information Auckland Regional Public Health Service (ARPHS) additional surveillance information National Measles Reference Laboratory - genotyping