Fourth Dose of BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting

BACKGROUND

With large waves of infection driven by the B.1.1.529 (omicron) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), alongside evidence of waning immunity after the booster dose of coronavirus disease 2019 (Covid-19) vaccine, several countries have begun giving at-risk persons a fourth vaccine dose.

METHODS

To evaluate the early effectiveness of a fourth dose of the BNT162b2 vaccine for the prevention of Covid-19-related outcomes, we analyzed data recorded by the largest health care organization in Israel from January 3 to February 18, 2022. We evaluated the relative effectiveness of a fourth vaccine dose as compared with that of a third dose given at least 4 months earlier among persons 60 years of age or older. We compared outcomes in persons who had received a fourth dose with those in persons who had not, individually matching persons from these two groups with respect to multiple sociodemographic and clinical variables. A sensitivity analysis was performed with the use of parametric Poisson regression.

RESULTS

The primary analysis included 182,122 matched pairs. Relative vaccine effectiveness in days 7 to 30 after the fourth dose was estimated to be 45% (95% confidence interval [CI], 44 to 47) against polymerase-chain-reaction-confirmed SARS-CoV-2 infection, 55% (95% CI, 53 to 58) against symptomatic Covid-19, 68% (95% CI, 59 to 74) against Covid-19-related hospitalization, 62% (95% CI, 50 to 74) against severe Covid-19, and 74% (95% CI, 50 to 90) against Covid-19-related death. The corresponding estimates in days 14 to 30 after the fourth dose were 52% (95% CI, 49 to 54), 61% (95% CI, 58 to 64), 72% (95% CI, 63 to 79), 64% (95% CI, 48 to 77), and 76% (95% CI, 48 to 91). In days 7 to 30 after a fourth vaccine dose, the difference in the absolute risk (three doses vs. four doses) was 180.1 cases per 100,000 persons (95% CI, 142.8 to 211.9) for Covid-19-related hospitalization and 68.8 cases per 100,000 persons (95% CI, 48.5 to 91.9) for severe Covid-19. In sensitivity analyses, estimates of relative effectiveness against documented infection were similar to those in the primary analysis.

CONCLUSIONS

A fourth dose of the BNT162b2 vaccine was effective in reducing the short-term risk of Covid-19-related outcomes among persons who had received a third dose at least 4 months earlier. (Funded by the Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.).

Comparing COVID-19-related hospitalization rates among individuals with infection-induced and vaccine-induced immunity in Israel

With the COVID-19 pandemic ongoing, accurate assessment of population immunity and the effectiveness of booster and enhancer vaccine doses is critical. We compare COVID-19-related hospitalization incidence rates in 2,412,755 individuals across four exposure levels: non-recent vaccine immunity (two BNT162b2 COVID-19 vaccine doses five or more months prior), boosted vaccine immunity (three BNT162b2 doses), infection-induced immunity (previous COVID-19 without a subsequent BNT162b2 dose), and enhanced infection-induced immunity (previous COVID-19 with a subsequent BNT162b2 dose). Rates, adjusted for potential demographic, clinical and health-seeking-behavior confounders, were assessed from July-November 2021 when the Delta variant was predominant. Compared with non-recent vaccine immunity, COVID-19-related hospitalization incidence rates were reduced by 89% (87–91%) for boosted vaccine immunity, 66% (50–77%) for infection-induced immunity and 75% (61–83%) for enhanced infection-induced immunity. We demonstrate that infection-induced immunity (enhanced or not) provides more protection against COVID-19-related hospitalization than non-recent vaccine immunity, but less protection than booster vaccination. Additionally, our results suggest that vaccinating individuals with infection-induced immunity further enhances their protection.

The relative degree of immunity to SARS-CoV-2 provided by combinations of natural infection, vaccination, and booster doses is unknown. Here, the authors show that infection-induced immunity provides more protection against COVID-19-related hospitalization than non-recent vaccine immunity, but less than booster vaccination.

The association between real-time reverse transcriptase polymerase chain reaction cycle threshold values, symptoms and disease severity among COVID-19 patients in the community: a retrospective cohort study

BACKGROUND

COVID-19 continues to spread throughout the world. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) is used to diagnose COVID-19, with its cycle threshold (Ct) value inversely related to the viral load. The association between Ct values and COVID-19 related outcomes has been studied in the hospital setting but less so in the community. We aimed to estimate the association between Ct values and the severity of community-diagnosed COVID-19 to provide evidence on the utility of Ct testing in this setting.

METHODS

This was a retrospective cohort study based on data from Israel's largest health organization. The study population included 34,658 individuals who tested positive for COVID-19 by RT-PCR and had available Ct values between June 1^st and December 21^st, 2020. Outcomes included COVID-19 related symptoms, hospitalization, severe disease, and death. Ct values were modelled both as discrete and continuous exposures.

RESULTS

After adjusting for known risk factors for severe COVID-19, low Ct values were associated with symptomatic disease (odds ratio [OR]: 1.51; 95% confidence interval [CI]:1.21-1.84), hospitalization (OR: 1.27; 95%CI: 1.12-1.49), severe disease (OR: 1.80; 95%CI: 1.43-2.27), and death (OR: 1.64; 95%CI: 1.06-2.59). By modelling the exposure as continuous, we noticed a dose-response relationship, with the risk gradually rising with lower Ct values.

CONCLUSIONS

This study found a significant association between low Ct values and severe COVID-19 related outcomes, with a dose-response relationship. This suggests that Ct values could be helpful in identifying high-risk patients diagnosed in the community.