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Fact Check-Conclusions about COVID-19 case rates fail to account for data differences

Articles shared online have made a misleading conclusion based on UK government data that COVID-19 vaccines increase the likelihood of a person catching the disease.

The articles (here , here) have pointed to the government’s weekly vaccine surveillance reports for their analysis (here).

On page 13 of the latest report (here), a table shows rates of COVID-19 infection are higher amongst those who have been double vaccinated and are over the age of 40.

For instance, the table shows the rate of infection for a person in their 40s who is double vaccinated is 1,731 cases per 100,000 people, while for those who have not received a vaccine it is 772.

This uses data on population from the National Immunisation Management System (NIMS) (here).

NIMS calculates the number of people in the country registered with a GP, which may overestimate the actual total (here).

This is because some people appear on old records with previous GP surgeries or stay registered when they have emigrated.

It also does not take account of people who are yet to register with a GP.

Therefore, while we do know the exact number of people vaccinated in England, (here), we do not know the exact number of unvaccinated, as we do not know the exact number for the whole population.

Another population estimate is available from the Office for National Statistics (ONS), which adjusts its figure based on data from the 2011 census.

This estimate is the best population estimate, according to the NHS (here and here), but it is still problematic due to its latest estimate being from mid-2020.

There are 7.1 million people aged 40-49 living in England (here), based on latest ONS data.

NIMS, on the other hand, estimates there are 8.1 million people in the same age bracket (here , here).

NHS England reports 6.4 million 40-49-year-olds have received at least one dose of a COVID-19 vaccine, while 6.1 million have received both (here).

This means that by NIMS’ estimates there are 1.7 million unvaccinated 40-49-year-olds in the country, while by ONS estimates there are 700,000.

Depending on which estimate you use, the COVID-19 infection rate varies significantly.

According to the latest government report showing data from Sept. 38 to Oct. 17 (page 13: here), there were a total 13,022 COVID-19 cases recorded in unvaccinated 40-49-year-olds.

A case rate per 100,000 people calculated using NIMS data is 772. Reuters also calculated the rate using ONS data, which is more than double – at nearly 1,900.

Underneath the data in the government report is a warning: “Interpretation of the case rates in vaccinated and unvaccinated population is particularly susceptible to changes in denominators and should be interpreted with extra caution.”

VERDICT

Missing context. Accurately calculating the COVID-19 infection rate for unvaccinated people is problematic because the exact population in England is not known, and different population estimates produce wildly different rates.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts here.

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