Breakthrough COVID-19 infection according to the infectious diseases hospital

Background. Despite the obvious successes of the world community in the fight against the spread of SARS-CoV-2, attempts to create new drugs that are active against the COVID-19 pathogen do not stop. In parallel, a targeted search for new prevention opportunities is being carried out. Vaccination does not protect 100% against possible infection, but significantly reduces the risk of developing severe forms of COVID-19, the need for hospitalization and death.

Aim. Describe the course of COVID-19 in patients previously vaccinated against this infection.

Material and methods. On the basis of the Republican Clinical Infectious Diseases Hospital of Kazan, from January 15 to August 28, 2021, an observational retrospective analytical study, which included the observation of 1260 patients who applied to the emergency room of the hospital and had a history of immunization against COVID-19, was conducted. Statistical data processing was carried out using an on-line calculator. The significance of differences between the compared groups was calculated using the χ2 test and Fisher's exact test. Gam-COVID-Vac as a specific prophylaxis was received by 87.8% (1106/1260), EpiVacCorona by 9.5% (120/1260), CoviVac by 2.6% (33/1260), Sputnik Light by 0.1% (1/1260). The assessment of adverse events after immunization was carried out taking into account the recommendations of the World Health Organization (2012).

Results. Laboratory-confirmed (or clinico-epidemiologically) “new coronavirus infection” was registered in 53.4% (673/1260) of patients. The proportion of cases of COVID-19 in each group vaccinated with a particular vaccine differed: among those vaccinated with Sputnik V it was 51.3% (567 people out of 1106 who applied), with EpiVacCorona — 71.7% (86 out of 120; p <0.001), KoviVak — 62.5% (20 out of 32). Side effects after immunization due to the action of the vaccine (previously such phenomena were called post-vaccination reactions) were registered in 1% (12/1260) of the vaccinated. Breakthrough infection (developing 14 days after the completed vaccination course) was recorded in 26.4% (333 out of 1260). It was characterized by a milder course and minimal manifestations on computed tomograms. The highest epidemiological efficacy among the three domestic vaccines (Gam-COVID-Vac, EpiVacCorona and KoviVac), according to our results, was shown by Gam-COVID-Vac. Those vaccinated with it fell ill with COVID-19 less frequently (33%, 365/1106) than those vaccinated with EpiVacCorona (56.7%, 68/120) and CoviVac (31.3%, 10/32), p <0.001 and p=0.836, respectively.

Conclusion. Breakthrough COVID-19 infection was characterized by a milder course, even among hospitalized ¬patients, exceptionally low mortality rate (0.9%, 3/333) in vaccinated compared to unvaccinated against SARS-CoV-2. Our study has shown that a full course of immunization reduces the incidence of moderate and severe forms of the disease.