Your questions about COVID-19 immunity answered

An update and summary of key findings so far
Since the start of the pandemic, PITCH (Protective Immunity from T Cells in Healthcare workers study) researchers from a combination of leading UK universities have been undertaking different studies on the immune response to Covid-19 with various healthcare workers across the UK.

Immune response after Covid-19 infection

Do I have sufficient protection if I’ve already had COVID-19?

Understanding the path of the immune response following infection with Covid-19 has been a key focus around the world from the beginning of the pandemic. As Professor Eleanor Barnes of Oxford University explains, gaining a detailed understanding of the immune response to Covid-19 is essential in reducing reinfections, tackling variants, and helping in the design of future vaccinations.

Before vaccines were available, PITCH researchers followed a group of 78 healthcare workers in detail at 5-6 time points each during a period of six months. They used SIMON, a machine learning approach, to predict response at 6 months after infection. In doing so, they considered a number of important questions including whether a natural infection provides protection against variants of concern and if there is any correlation between the severity of symptoms and long-term immunity.

As we now know to be the case with the general population, participants in the study showed a variable degree of immune responses six months after infection. These were defined by researchers via SIMON as high responders and low responders.

Using the same machine learning model, researchers were able to identify that the immune response at both the cellular level (one that does not involve antibodies) and humoral level (antibody-mediated immune response) increased one month after infection for high responders. This was further identified to be important for the maintenance of immunity six months after infection. In addition, these individuals (categorised as high responders) were also better able to neutralise variants of concern, like the Victoria, Alpha and Beta variants.

Conversely, those whose response was identified as low not only showed a reduction in the ability to neutralise the Victoria variant, but also a marked loss of ability to neutralise both the Alpha and Beta variants. This data and information are important as it tells researchers that immune events primed during a Covid-19 infection may define paths leading to effective maintenance or loss of long-term T and B cell immune memory. Critically, maintenance of immune memory over time is crucial to neutralising future variants of concern. 

Immune response after the first dose of Pfizer vaccine

What level of protection do I have after one dose of a vaccine?

In March 2021, PITCH researchers discovered and shared that 99% of people produce a strong immune response against COVID-19 following one dose of the Pfizer vaccine. The findings suggested that one dose protects against severe disease and supported the decision to delay the second dose by giving priority to administering the first dose to as many people as possible to provide protection to as many high-risk groups as possible. However, the study also further indicated that levels of protection were even stronger after two doses underlining the importance of people taking the second dose of the vaccine.

Immune response with different gaps in the first and second dose of Pfizer vaccine

How is my immunity affected by different gaps between the first and second dose?

In the most comprehensive study to date into the immune response to Covid-19 vaccines, aside from clinical trials, PITCH researchers studied 503 healthcare workers in Birmingham, Liverpool, Newcastle, Oxford and Sheffield, comparing short (median 3.4 weeks, range 2-5 weeks) and long (median 10 weeks, range 6-14 weeks) dosing schedules of the Pfizer vaccine. Their findings and insights include:

  • Antibodies fell over the 10 weeks after the first dose for people getting the longer dosing interval. However, T cell levels were well-maintained. As mentioned earlier, we now know that a single dose of vaccine gives substantial protection against COVID-19 and researchers believe T cells may be an important part in this. Taking a T Cell test in combination with a Roche quantitative antigen test is the recommended route and combination to fully understanding the level of your immune response to Covid19 vaccination.
  • Compared to the shorter dosing interval, the longer one resulted in 2 times higher neutralising antibodies against all tested variants of Covid19 including the Delta variant. Absolute numbers of T cells were lower after the long interval compared to the short interval between doses, however, the T cell response had more characteristics of a helper response (essential for all adaptive immune responses and helping other cells of the immune system) stimulating long term memory and antibody production.

It is important to note that irrespective of the gap in doses, the study found that levels of antibodies and T cells varied from person to person. Researchers believe this can be attributed to and be dependent on genetics, underlying health conditions, and past exposure to COVID-19 and other viruses. This finding is very important when magnified at the population level and it also underlines the importance of everyone getting two doses of the vaccine to boost their own protection, especially against variants of concern.

Are there ways to check my immunity?

You can read more about testing here and here.

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