BNT162b2 XBB1.5-adapted Vaccine and COVID-19 Hospital Admissions and Ambulatory Visits in US Adults (preprint)

ImportanceData describing the early additional protection afforded by recently recommended XBB1.5- adapted COVID-19 vaccines are limited. ObjectiveWe estimated the association between receipt of BNT162b2 XBB1.5-adapted vaccine (Pfizer- BioNTech 2023-2024 formulation) and medically attended COVID-19 outcomes among adults [≥]18 years of age. Design, Setting, and ParticipantsWe performed a test-negative case-control study to compare the odds of BNT162b2 XBB1.5- adapted vaccine receipt between COVID-19 cases and test-negative controls among adults in the Kaiser Permanente Southern California health system between October 11 and December 10, 2023. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated from multivariable logistic regression models that were adjusted for patient demographic and clinical characteristics. ExposureThe primary exposure was receipt of BNT162b2 XBB1.5-adapted vaccine compared to not receiving an XBB1.5-adapted vaccine of any kind, regardless of prior COVID-19 vaccination or SARS-CoV-2 infection history. We also compared receipt of prior (non-XBB1.5-adapted) versions of COVID-19 vaccines to the unvaccinated to estimate remaining protection from older vaccines. Main Outcomes and MeasuresCases were those with a positive SARS-CoV-2 polymerase chain reaction test, and controls tested negative. Analyses were done separately for COVID-19 hospital admissions, emergency department (ED) and urgent care (UC) encounters, and outpatient visits. ResultsAmong 4232 cases and 19,775 controls with median age of 54 years, adjusted ORs for testing positive for SARS-CoV-2 among those who received BNT162b2 XBB1.5-adapted vaccine a median of 30 days ago (vs not having received an XBB1.5-adapted vaccine of any kind) were 0.37 (95% CI: 0.20-0.67) for COVID-19 hospitalization, 0.42 (0.34-0.53) for ED/UC visits, and 0.42 (0.27-0.66) for outpatient visits. Compared to the unvaccinated, those who had received only older versions of COVID-19 vaccines did not show significantly reduced risk of COVID-19 outcomes, including hospital admission. Conclusions and RelevanceOur findings reaffirm current recommendations for broad age-based use of annually updated COVID-19 vaccines given that (1) XBB1.5-adapted vaccines provided significant additional protection against a range of COVID-19 outcomes and (2) older versions of COVID-19 vaccines offered little, if any, additional protection, including against hospital admission, regardless of the number or type of prior doses received. KEY POINTS QuestionsDoes receiving the BNT162b2 XBB1.5-adapted vaccine offer additional protection against COVID-19 hospital admission and ambulatory visits in US adults [≥]18 years of age compared to not receiving an XBB1.5-adapted vaccine of any kind? Do older versions of COVID-19 vaccine still provide any protection compared to the unvaccinated? FindingsThe BNT162b2 XBB1.5-adapted vaccine (Pfizer-BioNTech 2023-2024 formulation) provided significant additional protection against a range of COVID-19 outcomes during a period when XBB sub-lineages were predominant but JN.1 was also co-circulating and rapidly increasing in prevalence. Older versions of COVID-19 vaccines offered little, if any, additional protection compared to the unvaccinated, including against COVID-19 hospital admission, regardless of the number or type of prior doses received. MeaningOur findings reaffirm current recommendations for broad age-based use of annually updated COVID-19 vaccines.

Ischemic Stroke after Bivalent COVID-19 Vaccination: A Self-Controlled Case Series Study (preprint)

Introduction The potential association between bivalent COVID-19 vaccination and ischemic stroke remains uncertain, despite several studies conducted thus far. The purpose is to evaluate the risk of ischemic stroke following bivalent COVID-19 vaccination. Methods A self-controlled case series study was conducted among members aged 12 years and older who experienced ischemic stroke between September 1, 2022 and March 31, 2023 in a large California health care system. Ischemic strokes were identified using ICD-10 codes in Emergency Department and inpatient settings. Exposures were Pfizer-BioNTech or Moderna bivalent COVID-19 vaccination. Risk intervals were pre-specified as 1-21 days and 1-42 days after bivalent COVID-19 vaccination; all non-risk-interval person-time served as control interval. We conducted overall and subgroup analyses by age, history of SARS-CoV-2 infection, and co-administration of influenza vaccine. When an elevated risk was detected, we performed chart review of ischemic strokes, and re-evaluated the risk. RESULTS With 4933 cases, we found no increased risk within 21-day risk interval across vaccines and by subgroups. However, an elevated risk emerged within 42-day risk interval among individuals <65 years who received co-administration of Pfizer-BioNTech bivalent vaccine and influenza vaccine on the same day; relative incidence (RI) was 2.14 (95% CI, 1.02-4.49). Among those who also had history of SARS-CoV-2 infection, RI was 3.94 (95% CI, 1.10-14.16). After chart review, RIs were 2.35 (95% CI, 0.98-5.65) and 4.33 (95% CI, 0.98-19.11), respectively. Among individuals <65 years who received Moderna bivalent vaccine and had history of SARS-CoV-2 infection, RI was 2.62 (95% CI, 1.13-6.03) before chart review and 2.24 (95% CI, 0.78-6.47) after chart review. CONCLUSIONS The potential association between bivalent COVID-19 vaccination and ischemic stroke in the 1-42-day analysis warrants further investigation among individuals <65 years with influenza vaccine co-administration and prior SARS-CoV-2 infection.

Increased vaccine sensitivity of an emerging SARS-CoV-2 variant (preprint)

Host immune responses are a key source of selective pressure driving pathogen evolution. Emergence of many SARS-CoV-2 lineages has been associated with improvements in their ability to evade population immunity resulting from both vaccination and infection. Here we show diverging trends of escape from vaccine-derived and infection-derived immunity for the emerging XBB/XBB.1.5 Omicron lineage. Among 31,739 patients tested in ambulatory settings in Southern California from December, 2022 to February, 2023, adjusted odds of prior receipt of 2, 3, 4, and [≥]5 COVID-19 vaccine doses were 10% (95% confidence interval: 1-18%), 11% (3-19%), 13% (3-21%), and 25% (15-34%) lower, respectively, among cases infected with XBB/XBB.1.5 than among cases infected with other co-circulating lineages. Similarly, prior vaccination was associated with greater protection against progression to hospitalization among cases with XBB/XBB.1.5 than among non-XBB/XBB.1.5 cases (70% [30-87%] and 48% [7-71%], respectively, for recipients of [≥]4 doses). In contrast, cases infected with XBB/XBB.1.5 had 17% (11-24%) and 40% (19-65%) higher adjusted odds of having experienced 1 and [≥]2 prior documented infections, respectively, including with pre-Omicron variants. As immunity acquired from SARS-CoV-2 infection becomes increasingly widespread, fitness costs associated with enhanced vaccine sensitivity in XBB/XBB.1.5 may be offset by increased ability to evade infection-derived host responses.

Effectiveness of nirmatrelvir-ritonavir against hospital admission: a matched cohort study in a large US healthcare system (preprint)

ABSTRACT Background In the United States, oral nirmatrelvir-ritonavir (Paxlovid™) is authorized for use among patients aged ≥12 years with mild-to-moderate SARS-CoV-2 infection who are at risk for progression to severe COVID-19, including hospitalization. However, effectiveness under real-world conditions has not been well established. Methods We undertook a matched, observational cohort study of non-hospitalized individuals with SARS-CoV-2 infection to compare outcomes between those who received or did not receive nirmatrelvir-ritonavir within the Kaiser Permanente Southern California healthcare system. Individuals were matched on testing date, age, sex, treatment/care setting, symptoms status (including presence or absence of acute COVID-19 symptoms at testing, and time from symptom onset to testing), history of vaccination and SARS-CoV-2 infection, Charlson comorbidity index, and prior-year healthcare utilization. Time to hospital admission was compared between matched COVID-19 cases who received or did not receive nirmatrelvir-ritonavir. Primary analyses evaluated treatment effectiveness against any hospital admission and acute respiratory infection (ARI)-associated hospital admission, with dispense occurring 0–5 days symptom onset. Secondary analyses evaluated effectiveness against the same endpoints for all treatment dispenses. We measured treatment effectiveness as (1–adjusted hazards ratio [aHR])×100%, estimating the aHR via Cox proportional hazards models accounting for match strata and additional patient characteristics. Results Analyses included 4,329 nirmatrelvir-ritonavir recipients and 20,980 matched non-recipients who were followed ≥30 days after a positive SARS-CoV-2 outpatient test. Overall, 23,603 (93.3%) and 19,564 (78.1%) of 25,039 participants had received ≥2 and ≥3 COVID-19 vaccine doses, respectively. A total of 23,858 (94.2% of 25,039) patients were symptomatic at the point of testing, with a 2.1 day mean time from symptom onset to testing. For patients dispensed nirmatrelvir-ritonavir 0–5 days after symptom onset, effectiveness in preventing all hospital admissions was 88.1% (95% confidence interval: 49.0–97.5%) over 15 days and 71.9% (25.3–90.0%) over 30 days, respectively. Effectiveness in preventing ARI-associated hospital admissions was 88.3% (12.9–98.8%) and 87.3% (18.3–98.5%) over 15 and 30 days, respectively. In expanded analyses that included patients receiving treatment at any point during their clinical course, effectiveness was 86.6% (54.9–96.3%) and 78.0% (46.2–91.4%) in preventing all hospital admissions over 15 and 30 days, respectively, and 93.7% (52.5–99.4%) and 92.8% (53.9–99.1%) in preventing ARI-associated hospital admissions over 15 and 30 days. Subgroup analyses identified similar effectiveness estimates among patients who had received ≥2 COVID-19 vaccine doses. Implications In a real-world setting with high levels of COVID-19 vaccine and booster uptake, receipt of nirmatrelvirritonavir 0–5 days after symptom onset was associated substantial reductions in risk of hospital admission among individuals testing positive for SARS-CoV-2 infection in outpatient settings. Funding US Centers for Disease Control and Prevention, US National Institutes of Health

Association of SARS-CoV-2 BA.4/BA.5 Omicron lineages with immune escape and clinical outcome (preprint)

Expansion of the SARS-CoV-2 BA.4/BA.5 Omicron lineages in populations with prevalent immunity from prior infection and vaccination has raised concerns about the association of these lineages with immune escape. Here we show that COVID-19 vaccination and documented prior infection are associated with reduced protection against infection with BA.4/BA.5. Compared to time-matched BA.2 cases, BA.4/BA.5 cases had 9% (95% confidence interval: 2-17%) and 27% (15-41%) higher adjusted odds of having received 3 and 4 COVID-19 vaccine doses, respectively, and 55% (39-71%) higher adjusted odds of documented infection [≥]90 days previously. However, BA.4/BA.5 infection was not associated with differential risk of emergency department presentation, hospital admission, or intensive care unit admission following an initial outpatient diagnosis. This finding held after correcting for potential exposure misclassification resulting from unascertained prior infections. Despite increased risk of BA.4/BA.5 breakthrough infection observed among previously vaccinated or infected individuals, the reduced severity associated with prior (BA.1 and BA.2) Omicron lineages has persisted with BA.4/BA.5.