Protective action of natural and induced immunization against the occurrence of delta or alpha variants of SARS-CoV-2 infection: a test-negative case-control study

Dynamics of anti-SARS-CoV-2 antibodies in the Albanian population: Impact of infection- and vaccine-induced immunity during the COVID-19 pandemic

Objectives

Understanding immune response dynamics during the COVID-19 pandemic is crucial for optimizing future vaccine strategies. This study investigated the infection- and vaccine-induced SARS-CoV-2 antibody responses in the Albanian population from August 2021 to August 2022.

Methods

This used a cross-sectional approach, analyzing two independent, randomly selected population samples over 1 year. Participants' demographic, health, vaccination, and COVID-19 data were collected, with blood samples assessed via enzyme linked immunosorbent assay for immunoglobulin G class anti-spike and anti-nucleocapsid antibodies.

Results

By August 2022, all individuals receiving one vaccine dose achieved antibody levels comparable to those receiving two doses (median 7.71 index ratio [IR] vs 7.00 IR). In August 2021, those with previous COVID-19 infection receiving one vaccine dose showed median anti-spike immunoglobulin G levels of 7.22 IR compared with 4.84 IR in those without previous infection receiving two doses. However, individuals aged ≥61 years required two vaccine doses to achieve similar immune responses as younger individuals with one dose.

Conclusions

These findings underscore the importance of hybrid immunity, suggesting one vaccine dose may suffice for individuals with previous COVID-19 infection, whereas older adults require additional doses for optimal protection. This study provides insights into humoral immune response dynamics, which is crucial for refining COVID-19 vaccination strategies in middle-income countries with low vaccination coverage and high infection rates.

Estimating All-Cause Deaths Averted in the First Two Years of the COVID-19 Vaccination Campaign in Italy

Comparing deaths averted by vaccination campaigns is a crucial public health endeavour. Excess all-cause deaths better reflect the impact of the pandemic than COVID-19 deaths. We used a seasonal autoregressive integrated moving average with exogenous factors model to regress daily all-cause deaths on annual trend, seasonality, and environmental temperature in three Italian regions (Lombardy, Marche and Sicily) from 2015 to 2019. The model was used to forecast excess deaths during the vaccinal period (December 2020-October 2022). We used the prevented fraction to estimate excess deaths observed during the vaccinal campaigns, those which would have occurred without vaccination, and those averted by the campaigns. At the end of the vaccinal period, the Lombardy region proceeded with a more intensive COVID-19 vaccination campaign than other regions (on average, 1.82 doses per resident, versus 1.67 and 1.56 in Marche and Sicily, respectively). A higher prevented fraction of all-cause deaths was consistently found in Lombardy (65% avoided deaths, as opposed to 60% and 58% in Marche and Sicily). Nevertheless, because of a lower excess mortality rate found in Lombardy compared to Marche and Sicily (12, 24 and 23 per 10,000 person-years, respectively), a lower rate of averted deaths was observed (22 avoided deaths per 10,000 person-years, versus 36 and 32 in Marche and Sicily). In Lombardy, early and full implementation of adult COVID-19 vaccination was associated with the largest reduction in all-cause deaths compared to Marche and Sicily.

Elevated risk of infection with SARS-CoV-2 Beta, Gamma, and Delta variants compared with Alpha variant in vaccinated individuals

The extent to which severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) break through infection- or vaccine-induced immunity is not well understood. We analyzed 28,578 sequenced SARS-CoV-2 samples from individuals with known immune status obtained through national community testing in the Netherlands from March to August 2021. We found evidence of an increased risk of infection by the Beta (B.1.351), Gamma (P.1), or Delta (B.1.617.2) variants compared with the Alpha (B.1.1.7) variant after vaccination. No clear differences were found between vaccines. However, the effect was larger in the first 14 to 59 days after complete vaccination compared with ≥60 days. In contrast to vaccine-induced immunity, there was no increased risk for reinfection with Beta, Gamma, or Delta variants relative to the Alpha variant in individuals with infection-induced immunity.

Evaluation of the risk of SARS-CoV-2 infection and hospitalization in vaccinated and previously infected subjects based on real world data

The objective of our study was to determine the joint protective effect of a previous SARS-CoV-2 infection and vaccination on the risk of a new infection and hospitalization. Two case-control studies nested in a cohort of COVID-19 patients cared for by the Local Health Unit (LHU) of Vercelli, Italy, were performed, one to estimate the risk of infection and the second to estimate the risk of hospitalization. Each new infection and hospitalization was matched with up to 4 disease-free subjects who were the same age, sex and index date (i.e., controls). Study subjects were followed up from cohort entry date to disease outcome, end of follow-up or emigration. Vaccination was associated with a 36% (OR 0.64; 95%CI 0.62-0.66) and 90% (OR 0.10; 95%CI 0.07-0.14) reduction in the risk of infection and hospitalization, respectively. Prior infection was associated with a 65% (OR 0.35; 95%CI 0.30-0.40) and 90% (OR 0.10; 95%CI 0.07-0.14) reduction in the risk of infection and hospitalization, respectively. Vaccinated and recovered subjects showed a 63% (OR 0.37; 95%CI 0.34-0.14) and 98% (OR 0.02; 95%CI 0-0.13) reduction in the risk of infection and hospitalization, respectively. Vaccination remains an essential public health tool for preventing severe forms of COVID-19. Our study shows that vaccination or previous infection has a strong protective effect against Sars-CoV-2 hospitalization. The protective role against infection appears to be present although with a lower efficacy rate than that presented in the RCTs.

SARS CoV-2 reinfection rate is higher in the Omicron variant than in the Alpha and Delta variants

Background and objectives

Many mutations in variants for instance Delta and Alpha are associated with immune evasion and higher infectious potential. There are uncertainties regarding Omicron. In this regard, we aimed to compare the frequency of reinfection of SARS CoV-2 variants in our hospital between April 22, 2021 and January 26, 2022.

Method

The reinfection rates and demographic characteristics of a total of 27,487 COVID-19 patients infected with different SARS CoV-2 variants were examined.

Results

Reinfection was found in 26 (0.46%) of 5554 Alpha, 209 (1.16%) of 17,941 Delta, and 520 (13.0%) of 3992 Omicron variants. A statistically significant difference was observed between the reinfection rates of the variants (p = 0.000). The mean reinfection days were calculated as 204.4 ± 51.1 in the Alpha variant, 291.2 ± 58.2 in the Delta variant, and 361.2 ± 131.6 in the Omicron variant (p = 0.000). It was observed that 16.5% of reinfection cases caught COVID-19 for the second time 3–6 months after the first COVID-19 infection, 36.7% after 6–12 months, and 46.8% after more than 12 months. There was a significant difference between the times in reinfection cases. Most reinfections occurred more than 12 months apart. Among those with a reinfection time > 12 months, 0% had Alpha, 3.4% had Delta, and 96.6% had Omicron variants.

Conclusion

The highest reinfection rate was observed in the Omicron variant. Reinfection was approximately 30 times more frequent in the Omicron variant than in the Alpha variant and 10 times more frequent in the Delta variant.