Italian study assesses COVID-19 reinfection risk in previously infected and vaccinated individuals

In a recent study posted on Research Square* In a preprint server, a team of Italian researchers determined the risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection and hospitalization in individuals with vaccination and previous SARS-CoV-2 infection. I investigated.

Background

As of May 2022, the 2019 coronavirus disease (COVID-19) pandemic had 17 million confirmed cases and 165,000 deaths in Italy. The World Health Organization’s (WHO) proposed mitigation measures, such as lockdowns and wearing masks, were effective but failed to significantly reduce infections and mortality.

Studies have shown that immunity induced from previous SARS-CoV-2 infection reduces the risk of re-infection by almost 90.4% and remains effective for nearly 10 months after recovery. Furthermore, the vaccination program in Italy started in his second half of 2020, with 95.06% of his 12-year-old individuals completing his first vaccination by May 2022 and 92.42% receiving a booster dose. We have you covered.

However, with the emergence of Omicron subvariants containing mutations in SARS-CoV-2, spike protein areas that allow immune evasion, efficacy of Hybrid immunity against reinfection should be evaluated.

About research

In the current study, we conducted two case-control studies in COVID-19 patients enrolled at the Local Health Unit (LHU) in Vercelli, Italy, and tested vaccination against infections and hospitalization and previous SARS-CoV- 2 estimated the efficacy of immunity by infection. The researchers also evaluated the effects of SARS-CoV-2 Omicron variants on hybrid immunity and analyzed the efficacy of booster dosing. The role of chronicity in SARS-CoV-2 infection and hospitalization risk was also assessed.

Data analyzed included patient demographic information enrolled in the LHU, swab test information, vaccine administration dates and doses, admission and discharge dates, and the International Classification of Diseases, 9th Revision (ICD-9-CM ) Codes, Drug Delivery Information, and Chronic Prescription Fee Waivers.

The first case study evaluated the risk of infection in 31,832 individuals who tested positive for SARS-CoV-2 on nasopharyngeal swabs. In contrast, a second case study estimated the hospitalization risk of her 911 patients admitted to her LSU with COVID-19. Each patient was matched with four controls of the same sex and age who were not infected with SARS-CoV-2 or who were not hospitalized on the index day of each case study.

Previous infections were defined based on positive swab tests for SARS-CoV-2 from 1 March to 26 December 2020, but cases were not associated with positive swab tests after 27 December 2020. was decided on the basis of Vaccination was described using complete primary vaccination cycle and booster dose information. situation. Exposure was analyzed treating previous SARS-CoV-2 infection and vaccination status as independent and covariables. Reinfection was determined based on his second positive swab test 90 days after his initial infection.

A list of chronic medical conditions diagnosed in patients prior to the pandemic was used to create the COVID-19 Vulnerability Index. According to the Italian Ministry of Health’s classification of chronic diseases, individuals are classified on a scale of 0 to 3, with 0 being ‘no chronic disease’ to 3 being ‘very vulnerable’.

result

Results showed that vaccination reduced the risk of infection by 36% and the risk of hospitalization by 89% when vaccination and previous infection were assessed separately. Prior SARS-CoV-2 infection reduced the risk of reinfection and hospitalization by 65% ​​and 90%, respectively. Vaccinated individuals previously infected with SARS-CoV-2 had a 62% and 98% lower risk of reinfection and hospitalization, respectively.

A vulnerability index based on chronic health conditions showed that the very vulnerable (score 3) and the frail (score 2) had an 83% and 51% higher risk of hospitalization, respectively.

Adjusting the analysis for vulnerability index, vaccination alone reduced infection and hospitalization risks by 36% and 90%, respectively, whereas previously infected, unvaccinated individuals had a 65% reduction in infection risk. , reduced hospitalization risk by 90%. Vaccinated individuals previously infected with SARS-CoV-2 had a 63% and 98% lower risk of reinfection and hospitalization, respectively.

Omicron variants were highly effective in reducing immunity induced by vaccination and previous infections. After the emergence of the Omicron variant, the risk of disease in vaccinated individuals rose from 43% to 67%. An unimmunized, previously infected individual showed his 45% reduction in reinfection risk after the emergence of the Omicron variant compared to the 89% risk reduction seen before the Omicron epidemic. I was. Vaccinated and previously infected individuals also showed reduced protection against SARS-CoV-2 after the emergence of Omicron variants (60% compared to 79% pre-Omicron epidemic). %).

Conclusion

Overall, the results show that hybrid immunity from completed primary vaccination and previous SARS-CoV-2 infection significantly reduces the risk of reinfection and severe disease, even in individuals with chronic underlying disease. I showed that.

Immune evasion by the Omicron variant reduced the protective effect of vaccination and previous infection. The effectiveness of booster doses in increasing protection against infection and severe her COVID-19 should be investigated.

*Important Notices

Research Square publishes non-peer-reviewed, preliminary scientific reports and should not be taken as conclusive, to guide clinical practice/health-related actions, or to be treated as established information. .