Why are so many vaccinated people catching COVID-19? A Guide to Interpreting Statistics – SPICe Spotlight

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COVID-19 Statistics It is everywhere and can be changed daily. Some statistics can be interpreted in a misleading way. This blog explains which statistics tell us the effectiveness of the COVID-19 vaccine and which statistics cannot.

Is the COVID-19 vaccine effective?

Approximately 12 million COVID-19 vaccines have been administered in Scotland since the vaccination program began in December 2020 ()Public Health Scotland data, As of January 25, 2022):

• 92% of the population over the age of 12 receive at least one dose.
• A third or booster immunization is provided to all persons over the age of 18 and 73% receive it.

We know that vaccines are very effective in protecting individuals from the aggravation of COVID-19.Evidence of this comes from Vaccine efficacy study -Such EAVE II study in Scotland – Specially designed for this purpose.There is Consistent evidence from multiple studies That is, the risk of hospitalization or death from COVID-19 is more than 90% lower than those who have been vaccinated twice or three times compared to those who have not been vaccinated.

However, no vaccine is 100% effective. Cases, hospitalizations, and deaths of COVID-19 can still occur among vaccinated people. We also know that the effectiveness of vaccines declines over time. This means that vaccinated individuals are at increased risk of becoming severely ill with COVID-19 over time from the last vaccination.

COVID-19 Statistics of Scottish Population

Regular statistical report Such Weekly report from Scottish Public Health How many COVID-19 cases, hospitalizations and deaths were there in the Scottish population? Also, it is common to report the numbers for vaccinated and unvaccinated people separately. These simple rates can tell you about the impact on the population, for example, to signal the response of medical services, but comparing the rates does not tell you how effective the COVID-19 vaccine is.

for example, Public Health Scotland reports:In the second week of January 2022, the COVID-19 case rate in Scotland was that unvaccinated people (424 age standardization rate per 100,000) received the COVID-19 vaccine twice. It was lower than the people who did (886 per 100,000). ). However, this is an important point in interpreting these statistics. This does not mean that the vaccine is ineffective.

Underlying these simple rates are the important differences in risk, behavior, and testing between vaccinated and non-vaccinated groups. These “statistical biases” can distort comparisons between these groups and lead to misleading conclusions.

The reason is explained in detail in the blog post. Public Health Scotland And that UK Health and Security Agency.. These are summarized below.

1.1. The size of the unvaccinated population is known to be overestimated: this is an underestimated rate..

The rate calculation requires health outcome counts (cases, hospitalizations, or deaths) and population size data. Example: Five COVID-19 cases occurring in a population of 1000 people make up 500 cases per 100,000 people. The GP Registration Database (known as the Community Health Index (CHI)) is used to calculate the rate of public health in Scotland because it contains individual vaccination status and health results. People who have recently interacted with the NHS in Scotland (for example, when vaccinated) may still be in Scotland at the time the health outcome data were collected. This provides reliable population estimates and rates for vaccinated groups, especially those with booster immunization. In contrast, some people in the database will leave the country without unregistering from the GP.However, since there is no record in the database that they have left the country, they are included in the population of the unvaccinated group, and this population is that’s all-Estimated, so its rate is under-Estimated.

2.2. The behavior is different between the vaccinated and non-vaccinated groups.

Two public health agencies may be more health conscious of vaccinated people and are more likely to test for COVID-19 on a regular basis, compared to unvaccinated people. It states that it is likely to be identified as a case. More tests increase the chances of getting a positive test result and result in a higher case rate. Their social interactions are also different and can affect their exposure to COVID-19.

3.3. Vaccinated groups may be more vulnerable to COVID-19.

Vaccination was prioritized for individuals who were considered more sensitive or at higher risk. The first line included many who were at high risk for COVID-19 because of their age, occupation, or underlying health. Differences in vaccination rates for each age group It helps to show this priority. In addition, individuals in the priority group who received only one or two doses should have received them more than 6 months ago, and the protection provided by these doses was diminished.

In summary