MEASLES BULLETIN T his is a second year review of a four-year collaborative project (2003-2006) between the Government of China, World Health Organization, United Nations Children’s Fund, Japan International Cooperation Agency and the Centers for Disease Control and Prevention, Atlanta. The purpose of the project is to strengthen control of vaccinepreventable diseases, measles in particular, and to improve access to basic immunizations for children. The project aims to decrease measles mortality to near zero, to decrease measles cases to <5/100 000, to prevent circulating wild or vaccine-derived poliovirus to zero and to increase to >85% the proportion of children fully immunized at the county level. To achieve these objectives, the following strategies have been developed and conducted: (1) improving immunization services and increasing routine immunization coverage, (2) giving vitamin A supplementation in selected pilot counties, (3) conducting catch-up immunization activities, (4) increasing capacity for surveillance, and (5) improving monitoring of coverage. The second year review took place from 28 February to 4 March with the objective of determining the impact of the project strategies carried out in 2004 and developing recommendations for implementation of the project strategies in 2005. The review assessed the November 2004 catch-up measles/oral poliovirus vaccine (OPV) campaign, the measles surveillance system, introduction of immunization requirements for entry into school, pilot to strengthen routine Expanded Programme on Immunization (EPI) including vitamin A in six counties, and the EPI training course. Guizhou has a population (2003) of 38.7 million with 57% (50/87) of the counties at the poverty level (farmers income is 1,565 RMB [US$ 188] per capita). In 2002, it had one of the highest incidence rates of measles cases and deaths in China. In November 2004, the measles campaign targeted children aged 8 months to <13 years (7 947 290) in 8 prefectures except Qiannan, where a pilot measles vaccination campaign had been conducted in November 2003 as part of the project strategies. Part of an OPV campaign was combined with the measles campaign. The OPV campaign targeted all children <4 years in the entire province. The findings are as follows: reported coverage for measles vaccine was 98%; surveillance of adverse events
World Health Organization Regional Office for the Western Pacific Expanded Programme on Immunization
World Health Organization, Western Pacific Regional Office, Manila, Philippines Issue 5 May 2005 ISSN 1814 3601
Second Year Review of Accelerated Measles Control & Strengthening Routine Immunization Services Project, Guizhou, China f o l l o w i n g immunization reported 297 incidents (38/million); between 1 January25 February 2005, 71 suspected measles cases excluding 4 cases imported from other provinces were reported in Guizhou. Thirty seven (52.1%) had a serum sample, and of this, 20 (54.1%) were IgM(+) and 17 (45.9%) IgM(-) for measles. Qiannan Prefecture, whose campaign had been carried out in November 2003, reported a major decrease in measles case and an incidence from 1609 (43/100 000) in 2003 to 8 (0.21 / 100 000) in 2004. Requiring immunization before entry to school meant teachers were trained, students were screened and unimmunized students were referred for immunizations. The quality and completeness of this process was highly variable. A national coverage survey conducted in 2004 for routine EPI indicated 52% coverage for the four traditional vaccines and 21% for hepatitis B vaccine. The major contributing problem for low immunization coverage related to financial issues, such as a lack of EPI budget or village doctors not receiving a salary for EPI or central government funding was received but not distributed. The 2004 routine EPI coverage for DPT3 is reported as 88% (by Statistics Bureau 75%).
The process of strengthening routine EPI involved a threeday training course for 192 staff from the nine prefectures and all of the 87 counties. Training in EPI surveillance management system for 18 staff from all prefectures was also conducted. Strengthening routine EPI also focused on integrating vitamin A supplementation and yielded Coverage evaluated by prefecture in measles campaign 2004 varied results; in one county, the third dose was difficult to deliver but in general coverage increased from 50% in 2002 to 88% in 2004. Overall, the project has good political commitment, measles campaign shows a significant decrease in measles incidence, checking of immunization record at school entry serves as a good model although routine EPI has many years of under funding.
Coverage evaluated(%) > 95 (66 counties) (5 counties) (3 counties) (1 counties)
90 to 9 5 80 to 9 0 6 0 to 80
completed 2004 (12 counties) no survey (0 county)
MEASLES BULLETIN Estimating Population Immunity To Measles island countries, the Republic of Korea, and Singapore. As other countries start to bring measles under good control, they will also need to start monitoring population immunity. About the method
I
n September 2003, the WHO Regional Committee for the Western Pacific adopted resolution WPR/RC54.R3. The committee noted that 95% population immunity is essential to achieve measles elimination and is one of the three criteria in the operational definition of measles elimination i n t h e Field Guidelines for Measles Elimination . <http://www.wpro.who.int/health_topics/measles/publications.htm>
In July 2004, the Measles Task Force endorsed the operational definition and noted that 95% population immunity can be achieved by a scheduled two-dose measles vaccine or by a combination of scheduled and supplementary immunization activities (SIAs). The Field Guidelines for Measles Elimination provides general guidance on measuring population immunity (PI), including the potential role of serosurveys. Monitoring PI from routine coverage data needs to be the primary monitoring tool, with serosurveys used to validate the calculated immunity, if needed. This paper outlines some methodological issues in using reported coverage data to calculate population immunity and illustrates how it might have been used to prevent the 2003 outbreak in the Marshall Islands. When is calculation of population immunity useful? Measles is an epidemic disease. When the number of susceptible individuals reaches a threshold, there will be an epidemic spread of the virus if it is introduced into that population. In a population where measles is no longer endemic as a result of immunization, the number of susceptibles may have reached the epidemic threshold, but this will not be realized until a large outbreak occurs. Calculation of PI helps to identify if that population is close to the epidemic threshold, so that preventive measures (immunization campaign for the susceptibles) can be taken and prevent an epidemic. In countries where measles remains endemic, there will be little value in calculating PI. The age-specific incidence of measles cases will give an indication of the distribution of susceptibles by age. In the Western Pacific Region, measles has been well controlled for some time in several countries and areas including Australia, Brunei Darussalam, Hong Kong (China), Macao (China), Malaysia, Mongolia, New Zealand, the Pacific
Calculation of PI seems straightforward, as it requires multiplying vaccine coverage by vaccine effectiveness. But there are several methodological issues. Firstly, there is an uncertainty about precise coverage and effectiveness, compounded by the fact there are likely to be variations in both measures in different communities. Reported coverage is known to be unreliable in many areas – or there may be different measures of coverage. Vaccine effectiveness will be affected by the age of the recipient, and heat/light damage or errors in preparation or administration of the vaccine. Secondly, the relationship between first dose, second dose (if scheduled), and SIA doses is not always known. In theory, only those who had a first scheduled dose can get the second one. In practice, an individual child may be reported as having received a second dose without having the first dose. Similarly, it could be assumed that all those who received a scheduled measles vaccine would also get a dose during the SIA; alternatively that the SIA will reach the entire cohort equally. The different assumptions lead to different results for PI. In addition to the options for calculating PI, there is also uncertainty about the precise level of the epidemiologic threshold where the number of susceptibles become sufficient to trigger an epidemic. As a conservative and simplifying assumption, it has been proposed that one birth cohort is the threshold 1 . This does not mean that outbreaks cannot occur under the threshold. Measles virus introduced into a sufficient pool of susceptibles can cause widespread infection among the susceptibles, even if their number is under the threshold. Because of these uncertainties, the examples shown here are based on calculating a range; and that the threshold of one birth cohort is used as in the Americas.
continued on page 3
1
Quadros CA et al. 1996. Measles Elimination in the Americas. Journal of American Medical Association 275(3): 224-229.]
MEASLES BULLETIN continued from page 2
Another Example Marshall Islands The Republic of the Marshall Islands has 29 atolls with 5 major islands and a population of 57 000, with most living on the two major atolls. The last reported measles outbreak was in 1988, and there has been no reported case of measles from 1989 to 2003. (Measles virus appears to have stopped circulating in the Pacific island countries since 1998). Before 1998, the Marshall Islands had a one-dose measles schedule at nine months of age. A two-dose measles schedule was introduced in 1998 (at 12 and 13 months). Routine coverage varied from 36 to 93%. Three SIAs were conducted in 1994, 1998 and 2002, with reported coverage between 77-90%. The very low incidence of measles between 1989 and 2003 gave a false sense of security. By estimating the population immunity and hence accumulation of susceptibles since 1989, it can be seen that the accumulated susceptibles had reached critical levels by 2003 that could range from one to as high as more than twice of an average birth cohort. The introduction of the virus coupled with this high accumulation of susceptibles led to an outbreak that started in July and lasted until November 2003 with 828 cases predominantly in the urban centre of Majuro. Figure 1. Accumulation of susceptibles from 1989 using reported coverage data, Marshall Islands In another Pacific island country, an outbreak occurred in 1993 after more than 20 years of no exposure to measles. Since then only two cases were reported, one in 1998 and another in 2003. Measles vaccine is routinely given to children at 12 months and again at 15 months. A campaign took place in 1998 but data are not available. The proportion of susceptibles is calculated from 1994; the year after the last outbreak, but estimates from 1994 to 1997 are not precise without the data for the 1998 campaign. Figure 2 shows the accumulation of susceptibles assuming 90% vaccine coverage for the 1998 campaign. One might assume the birth cohorts before 1998 were protected, as the introduction of the measles virus in 1998 did not cause an outbreak. Figure 2. Accumulation of susceptibles from 1994-2003, assuming 1998 campaign achieved 90% coverage
3
Proportion of birth cohort susceptible
2.5
2
1.5
3
1
Proportion of birth cohort susceptible
2.5
0.5
2
0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
1.5
1
0.5
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
In Figure 1, the bars indicate the proportion of children born that year that are susceptible to measles with the dark blue representing the possible range. The yellow shaded area represents the possible range of cumulative proportion of children susceptible to measles . T h e horizontal red line represents one birth cohort, which represents the level of susceptibles where a large outbreak is probable following virus introduction. The green line represents 0.05% birth cohort, which is the ideal level of achieving 95% population immunity and minimizing the risk of an outbreak.
2003
0
In 2003, measles virus was imported from the Marshall Islands, but because the susceptibles was well below the epidemic threshold, it did not cause an outbreak. If the current trend of coverage rates for two doses of measles vaccine continues, the population would have high immunity. This means that if any measles importation were to occur, transmission would be limited and a generalized outbreak would be unlikely. Conclusion The experience of both Pacific island countries reinforces the importance of maintaining high levels of population immunity as a requirement to achieve measles elimination. A low incidence of measles alone is not a guarantee that the population is already protected, as susceptibles may be accumulating eventually leading to a large outbreak if measles virus is re-introduced.
MEASLES BULLETIN Health Ministers Meeting for the Pacific Island Countries
T
he biannual meeting of health ministers from the Pacific island countries was held in Samoa from 14 to 17 March 2005. Pacific island countries see immunization as one of the most cost-effective health intervention that has a direct impact on promoting wellness. The Expanded Programme on Immunization (EPI) in the Pacific and Papua New Guinea has made significant achievements: eradication of poliomyelitis and certification of the polio-free status in 2000; interruption of endemic measles virus transmission in the Pacific islands (except Papua New Guinea) since 1998; introduction of hepatitis B vaccine into the EPI schedules of all countries; high reported immunization coverage (>90%) for most countries; and the establishment of a regional electronic disease surveillance network - the Pacific Public Health Surveillance Network (PPHSN). Despite these successes, the EPI must continue to evolve and expand. Efforts to improve measles population immunity provide countries with an opportunity to introduce new vaccines, such as rubella vaccine, and increase the benefit immunization programmes have in preventing death and disability. Some countries have set a target date for measles elimination, e.g. 2008 for Fiji, and most have introduced a routine two-dose schedule for measles, with the remaining conducting regular SIAs. When outbreaks occurred following importation, such as in Marshall Islands, successful outbreak responses took place. Papua New Guinea has conducted immunization campaigns for measles and polio and has reported high immunization coverage. At the meeting, health ministers reaffirmed their commitment and support for EPI to ensure the Region remains secured against the reintroduction of previously eliminated diseases such as poliomyelitis. It was recommended that Pacific island countries and areas should: (1) work towards establishing a Pacific regional target date for measles elimination; (2) strengthen routine EPI by improving timely delivery of a hepatitis B birth dose and ensuring that new vaccines such as rubella and Hib are added appropriately when long-term funding and sustainable high immunization coverage can be ensured; and (3) work with donors and partners under the new Pacific Immunization Programme Strengthening initiative to assess and ensure that key programme areas are adequately supported and functional.
JP Chaine
Regional Workshop on Immunization for Pacific Island Countries and areas Representatives from Pacific island countries and areas met in Noumea, New Caledonia, from 9 to13 May 2005 to discuss the Pacific Immunization Programme Strengthening (PIPS) initiative that aims to strengthen immunization programmes in the Region. The initiative introduced by WHO and the United Nations Children’s Fund (UNICEF) in 2004 will be instrumental in ensuring that Pacific island countries are equipped to meet the regional goals for measles elimination and Hepatitis B control. The new goals of the Expanded Programme on Immunization (EPI) in the WHO Western Pacific Region provide Pacific island countries with a framework to achieve full benefit from current immunization vaccines, lock in past programmes and introduce new vaccines.
continued on page 5
MEASLES BULLETIN continued from page 4
External technical and financial assistance is being provided through PIPS in order to assist countries in meeting the regional goals. Pacific island EPI managers are expected to use the meeting to reflect on activities and achievements since the group last met in 2004 in Auckland, New Zealand, as well as plan for future activities under the initiative. Immunization programmes in the Pacific and the Western Pacific Region are at a critical period of development and, for many Pacific island countries require renewed attention and support.
Table 1. Measles cases, vaccination status and deaths (January to December 2004)* Classification Reported suspected Laboratory Epi-linked cases confirmed Confirmed cases Clinical Incidence rate Discarded (Total confirmed) F
Indicators Suspected cases immunized O
Pending
Deaths
Latest date reported to Western Pacific Regional Office
Type of report
American Samoa Australia Brunei Darussalam Cambodia China Cook Islands Fiji French Polynesia Guam Hong Kong (China) Japan Kiribati Lao People's Democratic Republic Macao (China) Malaysia Marshall Islands Micronesia, Federated States of Mongolia Nauru New Caledonia New Zealand Niue Northern Mariana Islands Palau Papua New Guinea Philippines Republic of Korea Samoa Singapore Solomon Islands Tokelau Tonga Tuvalu Vanuatu Viet Nam Wallis and Futuna Western Pacific Region
70 16 352 0
70† 6 80 0
0 0 0
0 272 0
0.35 (70) 4.47 (16) 2.49 (352) 0.00 (0)
0 0 -
0 0 -
14% (10) 18% (64) -
0 3 0
04-Apr-05 18-Apr-05 27-Jan-05 08-Dec-04
case data aggregate case data zero-reporting
2 69 1554 0 1491 2 0 0 38
2 31 0 97 0 0 2
0 0 0 21 0 0 0
0 21 0 1373 0 0 0
1.23 (2) 0.74 (52) 1.22 (1554) 0.00 (0) 26.36 (1491) 0.43 (2) 0.00 (0) 0.00 (0) 0.08 (2)
17 0 36
0 0 0
36% (25) 0.04% (64) 2 -
0 0 14 0 0 0 -
12-Apr-05 24-Mar-05 29-Mar-05 17-Mar-05 17-Mar-05 04-Apr-05 15-Apr-05 04-Apr-05 24-Mar-05
aggregate case data aggregate zero-reporting aggregate aggregate aggregate aggregate case data
34 0 0 1385 3025 55 0 96 0 0 0 0 1633 0 9822
0 0 51 10 0 96 0 0 0 0 3 0 448
0 0 8 0 0 0 0 0 0 0 0 0 29
0 0 1877 0 0 0 0 0 0 0 92 0 3635
0.88 (34) 0.00 (0) 0.00 (0) 24.25 (1385) 2.42 (1936) 0.02 (10) 0.00 (0) 2.26 (96) 0.00 (0) 0.00 (0) 0.00 (0) 0.00 (0) 0.12 (95) 0.00 (0) 1.77 (7097) F
1089 39 0 1,534 2715
0 6 0 4 10
22% (674) 11% (6) 46% (753) -
0 0 106 0 0 0 0 0 0 0 0 0 123
31-Dec-04
aggregate
10-Mar-05 zero-reporting 25-Apr-05 aggregate 25-Apr-05 aggragate 14-Mar-05 case data 23-Nov-04 case data 20-Apr-05 aggregate 31-Dec-04 case data 05-Apr-05 aggragate 05-Apr-05 zero-reporting 04-Apr-05 aggregate 19-Apr-05 aggregate 28-Mar-05 case data zero-reporting
* Data are based on country reports and other sources available to EPI/Western Pacific Regional Office. Incidence rate per 100 000 population (World Population Prospects: The 2002 Revision, New York, United Nations, 2002). O
Suspected cases immunized does not distinguish between 1 or 2 doses.
†
lab confirmed or epidemiologically linked to a laboratory confirmed case
MEASLES BULLETIN Table 2. Measles cases, vaccination status and deaths (January to May 2005)* Classification Reported suspected Laboratory Epi-linked cases confirmed American Samoa Australia Brunei Darussalam Cambodia China Cook Islands Fiji French Polynesia Guam Hong Kong (China) Japan Kiribati Lao People's Democratic Republic Macao (China) Malaysia Marshall Islands Micronesia, Federated States of Mongolia Nauru New Caledonia New Zealand Niue Northern Mariana Islands Palau Papua New Guinea Philippines Republic of Korea Samoa Singapore Solomon Islands Tokelau Tonga Tuvalu Vanuatu Viet Nam Wallis and Futuna Western Pacific Region Confirmed cases Incidence rate Discarded (Total confirmed) F
Indicators Suspected cases immunizedO
Clinical
Pending
Deaths
Latest date reported to Western Pacific Regional Office
Type of report
7
7†
0
0
0.04 (7)
0
0
28% (2)
0
05-May-05
case data
0
0
0
0
0.00 (0)
-
-
0
0
18-Mar-05
aggregate
240 0
12 0
73 0
155 0
4.24 (240) 0.00 (0)
0 -
0 -
36% (87) -
0 -
12-Apr-05 20-Apr-05
aggregate aggregate
6
-
-
-
0.15 (6)
-
-
-
-
31-Mar-05
aggregate
23 9
6 -
0 -
0 -
0.01 (6) 0.21 (9)
3 -
14 -
39% (9) -
0 -
04-Apr-05 03-May-05
case data aggregate
285
25
73
155
0.24 (268) F
3
14
0
* Data are based on country reports and other sources available to EPI/Western Pacific Regional Office. Incidence rate per 100 000 population (World Population Prospects: The 2002 Revision, New York, United Nations, 2002). O Suspected cases immunized does not distinguish between 1 or 2 doses. †
lab confirmed or epidemiologically linked to a laboratory confirmed case
Comments may be sent to Dr Ernest Smith smithe@wpro.who.int or Ms Margaret Hercules herculesm@wpro.who.int Please send quarterly data to Mr Dexter Bersonda at bersondad@wpro.who.int WORLD HEALTH ORGANIZATION Regional Office for the Western Pacific United Nations Avenue P.O. Box 2932 1000 Manila, Philippines Fax No. (632) 5211036, 5260279, 5260362 Tel. No. (632) 5288001