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MMWR Weeks
Standard week numbers and influenza seasons used in the U.S. Centers for Disease Control and Prevention (CDC) and associated with the Morbidity and Mortality Weekly Report (MMWR).
The MMWR week is the week of the epidemiologic year for which the National Notifiable Diseases Surveillance System (NNDSS) disease report is assigned by the reporting local or state health department for the purposes of MMWR disease incidence reporting and publishing.
This dataset is published as a convenience for interpreting data published on an MMWR week basis by the City of Chicago and other entities. We believe it to be correct but all use is at your own risk.
For further convenience, this link will bring up a query view of the dataset, limited to 2020-2029 and easily adjustable to any other desired range of years.
MMWR weeks have the following characteristics:
- Weeks start on Sundays.
- Week 1 of a year is the first week that contains at least four days in that year, in other words, the week containing the first Wednesday of the year. As a result, some years have 53 MMWR weeks.
- Each influenza season starts with MMWR Week 40.
The columns were calculated with the following Excel formulas (expressed in terms of the second data row where the first row is column headers and copied to all subsequent rows):
- Year: =YEAR(A3+3) -- The calendar year of the Wednesday following the Sunday on which the week begins.
- Week: =IF(D2=D3,C2+1,1) -- If the year is the same as the previous week, increment by 1. If not, start over at Week 1 of the new year.
- Influenza Season: =IF(C3<40,D3-1&"-"&D3,D3&"-"&D3+1) -- If the week is 39 or earlier, the influenza season is the previous calendar year through the current calendar year. If the week is 40 or later, the influenza season is the current calendar year through the next calendar year.
Although not referred to explicitly at the time, MMWR week numbers effectively began with the first issue of the MMWR in January 1952.
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Complete Metadata
| @type | dcat:Dataset |
|---|---|
| accessLevel | public |
| contactPoint |
{ "fn": "Jonathan Levy", "@type": "vcard:Contact", "hasEmail": "mailto:no-reply@data.cityofchicago.org" } |
| description | Standard week numbers and influenza seasons used in the U.S. Centers for Disease Control and Prevention (CDC) and associated with the <a href="https://www.cdc.gov/mmwr" target="_blank">Morbidity and Mortality Weekly Report (MMWR)</a>. The <a href="https://ndc.services.cdc.gov/wp-content/uploads/2021/02/MMWR_Week_overview.pdf" target="_blank">MMWR week</a> is the week of the epidemiologic year for which the <a href="https://www.cdc.gov/nchs/hus/sources-definitions/nndss.htm" target="_blank">National Notifiable Diseases Surveillance System (NNDSS)</a> disease report is assigned by the reporting local or state health department for the purposes of MMWR disease incidence reporting and publishing. This dataset is published as a convenience for interpreting data published on an MMWR week basis by the City of Chicago and other entities. We believe it to be correct but all use is at your own risk. For further convenience, <a href="https://data.cityofchicago.org/Health-Human-Services/MMWR-Weeks/ib44-qiqz/explore/query/SELECT%0A%20%20%60week_start%60%2C%0A%20%20%60week_end%60%2C%0A%20%20%60mmwr_week%60%2C%0A%20%20%60mmwr_year%60%2C%0A%20%20%60influenza_season%60%0AWHERE%20%60mmwr_year%60%20BETWEEN%202020%20AND%202029/page/filter" target="_blank">this link</a> will bring up a query view of the dataset, limited to 2020-2029 and easily adjustable to any other desired range of years. MMWR weeks have the following characteristics: - Weeks start on Sundays. - Week 1 of a year is the first week that contains at least four days in that year, in other words, the week containing the first Wednesday of the year. As a result, some years have 53 MMWR weeks. - Each <a href="https://www.cdc.gov/fluview/index.html" target="_blank">influenza</a> season starts with MMWR Week 40. The columns were calculated with the following Excel formulas (expressed in terms of the second data row where the first row is column headers and copied to all subsequent rows): - Year: <b>=YEAR(A3+3)</b> -- The calendar year of the Wednesday following the Sunday on which the week begins. - Week: <b>=IF(D2=D3,C2+1,1)</b> -- If the year is the same as the previous week, increment by 1. If not, start over at Week 1 of the new year. - Influenza Season: <b>=IF(C3<40,D3-1&"-"&D3,D3&"-"&D3+1)</b> -- If the week is 39 or earlier, the influenza season is the previous calendar year through the current calendar year. If the week is 40 or later, the influenza season is the current calendar year through the next calendar year. Although not referred to explicitly at the time, MMWR week numbers effectively began with the <a href="https://stacks.cdc.gov/view/cdc/291/" target="_blank">first issue of the MMWR</a> in January 1952. |
| distribution |
[ { "@type": "dcat:Distribution", "mediaType": "application/json", "describedBy": "https://data.cityofchicago.org/api/views/ib44-qiqz/columns.json", "downloadURL": "https://data.cityofchicago.org/api/v3/views/ib44-qiqz/query.json?accessType=DOWNLOAD", "describedByType": "application/json" }, { "@type": "dcat:Distribution", "mediaType": "application/xml", "describedBy": "https://data.cityofchicago.org/api/views/ib44-qiqz/columns.xml", "downloadURL": "https://data.cityofchicago.org/api/v3/views/ib44-qiqz/export.xml?accessType=DOWNLOAD", "describedByType": "application/xml" }, { "@type": "dcat:Distribution", "mediaType": "text/csv", "downloadURL": "https://data.cityofchicago.org/api/v3/views/ib44-qiqz/export.csv?accessType=DOWNLOAD" } ] |
| identifier | https://data.cityofchicago.org/api/views/ib44-qiqz |
| issued | 2026-07-13 |
| keyword |
[ "health", "public health" ] |
| landingPage | https://data.cityofchicago.org/d/ib44-qiqz |
| modified | 2026-07-15 |
| publisher |
{ "name": "data.cityofchicago.org", "@type": "org:Organization" } |
| theme |
[ "Health & Human Services" ] |
| title | MMWR Weeks |
