Objective:

To assess the protective effect of the vaccine against SARS-CoV-2 upon hospitalizations due to COVID-19 during the fourth epidemic wave in Queretaro, Mexico.

Methods:

This investigation was designed as a retrospective cohort study in patients with COVID-19 during the fourth wave of the epidemic (December 19th, 2021, to January 9th, 2022). The exposed group consisted in those subjects who had received a vaccine against COVID-19 (genetically modified adenovirus vaccine and messenger ribonucleic acid vaccine); and the non-exposed group consisted in those people who were not vaccinated. Diagnosis of COVID-19 was made with a rapid antigenic test in oropharyngeal exudate, and the test was performed between the first and fifth day after the onset of symptoms. All patients who came to healthcare facilities because of symptoms, with a positive test and having received two doses of the vaccine. Statistical analysis included chi-square, relative risk, and confidence intervals (CI) for the relative risk.

Results:

Fifty-two patients who received a genetically modified vaccine, 119 who received a messenger ribonucleic acid vaccine, and 336 non vaccinated subjects were included in the study. The frequency of hospitalization was 62,2% in non-vaccinated persons, this rate was 23,1% (p<0.001), and relative risk was 0,37 (95% CI; 0,22-0,61) in those who received a genetically modified adenovirus vaccine, and it was 1.7% (p<0.001), and relative risk was 0,03 (95% CI; 0,006-0,10) in those who received the messenger ribonucleic acid vaccine.

Conclusions:

From a population point of view, the vaccine against COVID-19 was effective for preventing hospitalization in patients with acute COVID-19 disease during the fourth epidemic wave.

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