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Why does Omicron seriously affect European states with high vaccination rates?

Dimitar Ferdinandov

The Omicron variant of the SARS-CoV-2 utterly baffled the scientific community with its worrying amount of mutations, unexpected behaviour, and the emergence of the strain itself. The new variant was able to quickly spread worldwide and pushed many countries to reintroduce strict anti-epidemic measures. Many opponents to the mass vaccination campaigns use the opportunity to blame the surge of cases and the emergence of the variant on the vaccines. However, it was mass immunisation that played a key role in reducing the damage that Omicron inflicted on the European continent.

Caused by the immunisation campaign?

The opponents to the mass vaccination campaigns are trying tirelessly to connect the emergence of the Omicron variant to the vaccine administration efforts. The record number of mutations to the spike protein they argue is caused by the selective pressure vaccines impose on the virus. Fortunately, evidence for such a relationship is yet to be found. On the contrary, the binding affinity and neutralising capacity of the antibodies and memory cells, elicited as a consequence of the immunisation, have not been observed to dramatically decrease, despite the many mutations. (Nemet, 2021) (GeurtsvanKessel, 2021) What is observed, however, is that the virus is able to delay the immune response while being better at infecting cells. The mutations on the spike protein Omicron carry, which are more related to fitting with the body’s cells, are most likely the result of a long-term retention of the virus in a patient’s body. South Africa is battling the highest prevalence of AIDS in the world, with nearly 20% of people aged 19 to 49 living with HIV. This means that a significant percentage of the south african population is immunocompromised, and a weaker immune system allows the virus to remain in the body for an extended amount of time, and thus, allowing it to mutate and adapt to cells in the mucosa and the organs.

Cases are not that important

In European states with high vaccination rates, the surge of cases hardly causes an increase in hospitalizations and deaths. If we take the example of Great Britain, which reported 914,723 cases in the last week (December 22, 2021 – December 29, 2021), only 6,878 people were newly hospitalised (1 in 133 patients) during the same period, and 516 people lost their lives. (or 1 in 1773 infected). In Bulgaria for the last week 10,542 cases have been confirmed and 2,254 have been admitted to hospital (or 1 hospitalised in 4 confirmed cases). 460 people died (or 1 in 23 infected). For Bulgaria, the actual ratios may be higher due to underreporting and hesitance of citizens to take an official diagnostic test.

Why does the virus seem to easily affect people with immunity - acquired due to vaccination or illness?

The quick and easy answer is that the specific immune response is not immediate and takes time allowing for the infected person to receive a positive result from a diagnostic test or develop mild symptoms. It is important to remember that the vaccine is not an active agent that further protects the body. The vaccine trains the immune system on how to respond to a pathogen. Because it can be dosed, the vaccine contains (or produces in the body) the golden amount of antigens to which the immune system can develop good immunity.

How does the immune system respond to respiratory viruses?

The issue with SARS-CoV-2 (the COVID-19 virus) and other mucosal viruses (influenza, rhinoviruses, etc.) is that they cause infection before they can be detected by the immune system. The mucosa is the first line of defence of the organs in the human body. The epithelial cells that comprise it are actually made to be infected. When this happens, they begin to produce signalling proteins called interferons, which activate the immune system and help it localise the infection.

Once the infection is localised, some immune cells begin to study the pathogen, others seek for specialised immunocompetent cells that know how to deal with the infection. These first cells that come in contact with the infection are part of the innate (or natural) immunity. They do not know how to respond specifically to a pathogen. They are tasked with limiting the spread of the infection and bringing the specialised B and T lymphocytes that carry the specific immune response to the infection.

In the meantime, the cells of the innate immunity take crucial steps to reduce the damage done. Examples of key actions are the change in body temperature and the introduction of blood to the site of infection (i.e. inflammation). Those symptoms are inflicted in order to hinder the spread of the pathogen and to aid the efforts of the immune system. As the blood floods the infected area, in addition to more immune cells, come the Complement System (assisting proteins) and the infamous neutralising antibodies.

Antibodies attach to key pathogen proteins. In viruses, they prevent the infection of cells by making the connection between the virus and the cell impossible. The antibodies capable of neutralising SARS-CoV-2 attach to the spike (S) protein, which prevents the virus from binding to the ACE-2 membrane enzyme that the virus uses as a gateway to the insides of the cell.

What is decisive for the rapid neutralisation of respiratory viruses and how Omicron tilts the scales in its favour?

The sooner the infection is detected, the sooner the antibodies are introduced and B and T lymphocytes deal with the virus, allowing for a milder illness.

In Delta and especially Omicron variants of SARS-CoV-2, mutations have been observed on one of the non-structural proteins of the virus, which allow the virus to interfere with the secretion of interferons (the proteins that signal about the infection to the immune system), thereby significantly delaying its detection. Moreover, both variants have mutations in the spike (S) protein that allow for easier and faster infection. The Omicron variant has similar mutations in unprecedented quantities. This means that the variant is able to more quickly create a significant infection in the upper respiratory tract, while keeping the immune system at bay. Numerous copies of the virus easily fill respiratory droplets to leave the body of the infected patient – by them talking, sneezing, or coughing – and lead to the infection of others.

What can we do to protect ourselves?

Since we cannot control how fast the immune system detects the infection, we need to ensure an adequate and rapid immune response after the virus is detected to avoid serious illness. This can happen if the immune system is well prepared and has the necessary resources – antibodies and T and B lymphocytes. The immune system is best prepared by vaccination, so it is extremely important that more people, especially those at risk, be immunised or re-immunised with a booster dose. (Nemet, 2021) (GeurtsvanKessel, 2021)

How will Omicron affect Bulgaria?

It is early to say and extremely difficult to predict the impact of the variant on countries with lower vaccination rates such as Bulgaria. So far, Omicron has spread mainly within European countries that have strong immunity within the population. Due to the high rates of vaccination, most of these states welcomed the variant with almost no anti-epidemic measures in place, allowing it to easily spread. In such countries, the virus seems to be less pathogenic, but there is no way to know what would happen in Bulgaria. Research data in South Africa—a country with low vaccination rate—is extremely contradictory. Data from some studies suggest a reduced risk of hospitalisation with Omicron compared to Delta (Wolter, 2021), while others find an increased risk of hospitalisation even for the vaccinated (Collie, 2021). It’s too early to know, so the best strategy right now is to be more proactive and to try to protect ourselves.


  • Nemet, I., Kliker, L., Lustig, Y., Zuckerman, N., Erster, O., Cohen, C., Kreiss, Y., Alroy-Preis, S., Regev-Yochay, G., Mendelson, E., & Mandelboim, M. (2021). Third BNT162b2 Vaccination Neutralization of SARS-CoV-2 Omicron Infection. New England Journal of Medicine.

  • Wolter, N., Jassat, W., Walaza, S., Welch, R., et al. (2021). Early assessment of the clinical severity of the SARS-CoV-2 Omicron variant in South Africa. MedRxiv, 2021.12.21.21268116.

  • Collie, S., Champion, J., Moultrie, H., Bekker, L.-G., & Gray, G. (2021). Effectiveness of BNT162b2 Vaccine against Omicron Variant in South Africa. New England Journal of Medicine.

  • GeurtsvanKessel, C. H., Geers, D., Schmitz, K. S., et al. (2021). Divergent SARS CoV-2 Omicron-specific T- and B-cell responses in COVID-19 vaccine recipients. medRxiv, 2021.2012.2027.21268416.

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