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BackEntry title:

COVID-19 cases percentage change compared with previous 7 days

Last updated on Wednesday, 12 February 2025 at 10:32am

Summary

Topic
COVID-19
Category
headline
API name
COVID-19_headline_cases_7DayPercentChange

Rationale

The timely identification of cases is important to controlling the spread of COVID-19 and reducing the burden on healthcare systems.

Definition

This metric shows the percentage change in the number of reported new cases in the last 7 days as a percentage of the number of reported new cases in the previous 7 days.

New cases are reported by specimen date - the date the first sample that identified the infection was taken from an individual.

Methodology

COVID-19 cases are identified by taking specimens from people and testing them for the SARS-CoV-2 virus. If the test is positive, this is a case.

Cases identified using two types of test for the SARS-CoV-2 virus are reported on the dashboard:

  • polymerase chain reaction (PCR) tests, which require processing in a laboratory
  • rapid lateral flow virus (LFD) tests, which are swab tests that give results in less than an hour, without needing to go to a laboratory

All lateral flow tests reported via the “Report a COVID-19 rapid lateral flow test result” GOV.UK service are included. The service cannot be used to report results from test kits that are paid for. Therefore, results from paid for test kits are not included in figures on the dashboard.

People who test positive again after a given time period are counted as new cases. In England people are counted as new cases if they test positive again more than 90 days after their last positive test.

Data for the last 5 days by specimen date are considered incomplete as it takes time to get test results and record them on relevant lab systems. Cases data for England includes all positive lab-confirmed PCR test results plus, positive rapid lateral flow tests unless followed by a negative PCR test taken within 72 hours.

To calculate the percentage change in reported new cases, we take the difference between two metrics:

  • the total number of daily cases in the 7 days up to and including the most recent date with “complete” data (that is, 5 days before the current date)
  • the total number of daily cases in the previous 7 days

We then divide the difference between the total number of daily cases in the previous 7 days.

Caveats

This figure will underestimate the actual number of COVID-19 infections due to people not testing or not being able to report LFD results.

The percentage change includes newly-reported cases and adjustments to previously-reported cases – these may go up or down.

A change from 0 to a number greater than 0 will be displayed as 100% increase. A change from a number greater than 0 to 0 will be displayed as -100%, that is a 100% decrease.

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