Celebrating two years of COVID-19 serosurveillance.

We have tracked COVID-19 infection and vaccination rates in Wales for the last two years through serological surveillance. Serological surveillance (known as serosurvillance) involves measuring antibodies in the blood to estimate population immunity. The project was initially established during the first wave of COVID-19 in 2020 alongside Public Health Wales, Swansea Bay University Health Board and Cwm Taf Morgannwg University Health Board.

We provide samples and demographic information to the scheme. We currently process an average of 2000 samples per month and have processed over 66,000 samples.

COVID-19 monitoring did not track mild or asymptomatic infections at the start of the pandemic. We needed to find a way to gather information on the spread of COVID-19 without solely focusing on severe cases.

We discussed using donor samples to track immunity to the COVID-19 virus in the Welsh population with Public Health Wales. We can do this through measuring antibody levels in the blood.

Recognising testing support was needed, Swansea Bay University Health Board and Cwm Taf Morgannwg University Health Board were introduced to conduct antibody testing required for the serosurveillance.

We use samples that would otherwise be wasted for this project. Samples came from donors across the country, which helped estimate immunity levels in different parts of Wales.

By the end of 2020, we had set up a scientifically robust way to estimate immunity from the samples.

Another test was added later in 2021 to measure antibodies from vaccination, allowing us to track immunity and see how vaccines protect the population.

We can also relate some of the blood samples tested to the same donors who regularly donate throughout the year, allowing us to see changes in immunity over time and estimate how long immunity lasted.

Our project provides month-on-month estimates of the number of people with antibodies to the COVID-19 virus. From this, health bodies and Welsh Government can decide on vaccination plans and safety measures.

The vast majority of our blood donors are vaccinated. 99.6% of donors tested in this scheme have vaccine antibodies. Data gathered through the project revealed the older you are, the less likely you are to have antibodies. The emerging picture is Welsh Government may promote vaccination boosters for older people this winter. Younger people also have high rates of vaccine antibodies but are also seeing higher amounts of infection.

Our donor population tend to be healthy and fit, but we can conclude the same is happening across the general population.

We are continuing this scheme for the rest of 2022 at least. We know some people have antibodies for a long time, whereas others produce lower amounts of antibodies for shorter periods.

This information can be used to make decisions about vaccine booster timing. So, donors should take pride in knowing their donations can help inform the best course of action for the Welsh population.