The impact of vaccination against the new coronavirus infection on the morbidity of university students

BACKGROUND: Vaccination is currently considered the most successful strategy against the SARS-CoV-2 virus. However, cases of infection despite vaccination, so-called breakthrough infections, have been reported worldwide.

AIM: To evaluate the impact of vaccination against the new coronavirus infection COVID-19 on the morbidity of university students.

MATERIALS AND METHODS: The incidence of new coronavirus infection (COVID-19) among the students of North-Western State Medical University named after I.I. Mechnikov (further University) from September 1 to December 15, 2020 and 2021 was analyzed. There were 4876 and 4681 students under observation. Data on vaccination, probable site of transmission infection were collected by interviewing the ill people. Statistical processing of data was performed using EpiInfo software.

RESULTS: For the analyzed period 191 cases of COVID-19 among students were detected, the incidence of COVID-19 was 4.08 per 100 students, for the same period of the academic year 2020 it was 5.50, despite the fact that the incidence among St. Petersburg residents in 2021 was 1.75 times higher than in 2020. Re-infection was detected in 35 (18.3%) cases, 18 of whom were also vaccinated against COVID-19. A probable place of transmission infection was established in 36.1% of the cases, the most frequent being contact with a patient at their place of work in a health-care facility. By December 15, 2021, a total of 62.8% of students had been vaccinated against COVID-19. The incidence among vaccinated students was 2.72 per 100 students and 4.94 per 100 among unvaccinated students. A risk factor for breakthrough infections after vaccination was close contact with the source of infection: vaccinated persons had close contact in 50% of cases, compared with 28.9% of unvaccinated persons. The most important were contact with a patient in a health care setting and having multiple sources of infection, 31.1% and 5.6%, respectively.

CONCLUSIONS: Vaccination against COVID-19 was an effective preventive intervention. A risk factor for disease after vaccination is close contact with the source of infection. Establishment of collective immunity after vaccination is decisive for the vaccination-to-disease ratio, which starts to develop with 70-80% of vaccinated individuals. The use of a mask in public places and social distancing remain important preventive measures.