Immunity - HackMD

--- title: Immunity tags: live-v0.2.2, facts permalink: none at the moment, embedded in two facts pages --- The issue of waning immunity is an essential one, especially at the current time when many people worldwide have now received a COVID-19 vaccination. Two components play a role here. First, the time that has passed since the last vaccination and second, whether there are new variants of the virus that have an influence on the effectiveness of the vaccine. ### Basic components in the immune response to COVID-19 The immune system and the components involved are the subject of much more in-depth study, but the most important factors include: **Antibodies.** You've probably already heard the term antibodies discussed in the context of vaccines, referring especially to the neutralising antibodies that are responsible for protecting us against infection or transmission. The production of these antibodies is induced by vaccination or infection. Studies have shown that the number of antibodies decline after a certain time after immunisation, so that the ability to protect us from infection decreases ([Naaber et al., 2021](https://www.thelancet.com/journals/lanepe/article/PIIS2666-7762%2821%2900185-X/fulltext)). Fortunately, the body has more mechanisms at its disposal. For example, the long lasting memory B-cells. They help to induce renewed antibody protection, whenever our body gets into contact with the virus. Findings to date show that they last much longer than just a few months ([Ciabattini et al., 2021](https://www.frontiersin.org/articles/10.3389/fimmu.2021.740708/full)). **T-cells.** Additionally, there are white blood cells that we call T-cells. Their production is also induced by vaccination or infection. These T-cells are important in controlling the severity of disease we experience ([Tan et al., 2021](https://www.cell.com/cell-reports/fulltext/S2211-1247(21)00041-3)). This means that [even if you may get an infection, the risk of hospitalisation or death due to COVID-19 decreases](https://www.theatlantic.com/science/archive/2021/12/t-cells-omicron-vaccine-immunity/620995/). Antibody and T-cell counts increase again after booster vaccinations with mRNA vaccines such as Pfizer-BioNTech and Moderna. A large-scale study, in which a wide variety of vaccination regimens were tested, showed that it did not matter which vaccine was used for the prior vaccinations: as long as a mRNA vaccine was used for a booster shot, the protective ability was good ([Munro et al., 2021](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)02717-3/fulltext)). ### Immunity and COVID-19 variants Just as science evolves, so does the virus. The kind but also the count of antibodies needed to adequately protect against infection has unfortunately changed due to the emergence and rapid spread of the Delta and now the Omicron variant. Already with the Delta variant, it has been shown that the effectiveness of two vaccinations is reduced compared to prior variants ([Pouwels et al., 2021](https://www.nature.com/articles/s41591-021-01548-7); [Planas et al., 2021](https://www.nature.com/articles/s41586-021-03777-9)). In addition, with the waning immunity over time, the protection against infection is reduced ([Tartof et al., 2021](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)02183-8/fulltext)). ### How do boosters help? A booster vaccination increases the antibody count again and therefore decreases the risk of so-called "breakthrough infections" due to variants such as Delta ([Demonbreun, 2021](https://www.medrxiv.org/content/10.1101/2021.11.19.21266555v1). These booster vaccinations are also needed to further restore the ability of antibodies to neutralise the Omicron variant ([GeurtsvanKessel, 2021](https://www.medrxiv.org/content/10.1101/2021.12.27.21268416v1.full.pdf)). The increasing antibody count after the booster vaccination can induce an effective response against this new variant ([Garcia-Beltran et al., 2022](https://www.sciencedirect.com/science/article/pii/S0092867421014963)), even if it is just for a short time. Studies have shown that the antibody count declines again after a short while ([Wilhelm et al., 2021](https://www.medrxiv.org/content/10.1101/2021.12.07.21267432v1.full.pdf)) But it is again the T-cells that give us hope here for continued protection: current studies have shown that the T-cell response, which is induced through vaccination, is effective across the variants---including Omicron. This means that a booster vaccination is still very important to protect us against severe infections ([GeurtsvanKessel, 2021](https://www.medrxiv.org/content/10.1101/2021.12.27.21268416v1.full.pdf)). In Israel, the effectiveness of a second booster vaccination is currently being tested, especially to [discuss protection against the increasingly dominant Omicron variant](https://investors.biontech.de/de/news-releases/news-release-details/pfizer-und-biontech-geben-update-zur-omikron-variante). Some of the vaccine manufacturers are already [testing the development of an adapted vaccine in parallel](https://investors.modernatx.com/news/news-details/2021/Moderna-Announces-Strategy-to-Address-Omicron-B.1.1.529-SARS-CoV-2-Variant/default.aspx). The results of this and the development of the variants will show what further measures and vaccine recommendations will look like.