Effectiveness of Bivalent mRNA COVID-19 Vaccines in Preventing COVID-19–Related Thromboembolic Events Among Medicare Enrollees Aged ≥65 Years and Those with End Stage Renal Disease — United States, September 2022–March 2023

Results

Bivalent Vaccine Coverage

During September 4, 2022–March 4, 2023, among 12,706,176 immunocompetent Medicare beneficiaries aged ≥65 years who had previously received an original COVID–19 vaccine, 5,683,208 (44.7%) received a bivalent dose (Table 1). Overall, higher percentages of bivalent vaccine recipients than nonrecipients resided in an urban area (83% versus 78%), had received an influenza vaccine during the 2021–22 season (82% versus 55%) and 2022–23 season (87% versus 50%), and had received an original monovalent booster vaccine dose (96% versus 73%).

Among 78,618 Medicare beneficiaries aged ≥18 years with ESRD receiving dialysis who did not have additional immunocompromising conditions and had previously received original COVID-19 vaccine, 23,229 (29.5%) received a bivalent dose, including 7,239 (31.2%) aged 18–64 years and 15,990 (68.8%) aged ≥65 years. Similar to beneficiaries aged ≥65 years, among recipients with ESRD receiving dialysis, a higher percentage of those who received a bivalent vaccine dose compared with those who had not, had also received an influenza vaccine during the 2021–22 season (90% versus 82%) and the 2022–23 season (92% versus 79%) and had received an original monovalent booster vaccine dose (90% versus 74%). In addition, a higher percentage of bivalent COVID-19–vaccinated ESRD beneficiaries were older (69% were aged ≥65 years) and non-Hispanic White (53%) compared with those who did not receive the bivalent COVID-19 vaccine (59% and 47%, respectively).

Vaccine Effectiveness in Preventing COVID-19–related Thromboembolic Events

During the study period, COVID-19–related thromboembolic events were recorded among 22,001 immunocompetent beneficiaries aged ≥65 years and 1,040 immunocompetent beneficiaries aged ≥18 years with ESRD receiving dialysis (Table 2). A total of 1,505,533,898 original-vaccine–only person-days were contributed by immunocompetent beneficiaries aged ≥65 years, during which 17,746 COVID-19–related thromboembolic events were identified (Table 3). Among adults aged ≥65 years, 694,184,995 bivalent-vaccine person-days were contributed, during which 4,255 COVID-19–related thromboembolic events were identified. Adjusted VE against COVID-19–related thromboembolic events among immunocompetent beneficiaries aged ≥65 years was 47%, with lower VE estimates ≥60 days after bivalent vaccine receipt (42%) compared with VE estimates 7–59 days after bivalent vaccine receipt (54%).

Similarly, a total of 10,395,534 original-vaccine-only person-days were contributed by beneficiaries aged ≥18 years with ESRD receiving dialysis, during which 917 COVID-19–related thromboembolic events were identified. A total of 2,394,731 bivalent vaccine person-days were contributed, during which 123 COVID-19–related thromboembolic events were identified. Adjusted VE against COVID-19–related thromboembolic events was 51%, with lower VE estimates ≥60 days after bivalent vaccine receipt (45%) than 7–59 days after bivalent vaccine receipt (56%); however, these differences were not statistically significant (i.e., the 95% CIs overlapped).

Similar results were seen among beneficiaries aged ≥65 years with immunocompromise (overall bivalent VE = 46%, with 55% VE 7–59 days after receipt of vaccine, and 39% VE ≥60 days post-vaccination) and among beneficiaries with ESRD receiving dialysis and who had additional immunocompromising conditions (overall bivalent VE = 45%, with 60% VE 7–59 days after receipt of vaccine, and nonsignificant 30% VE at ≥60 days post-vaccination) (Supplementary Table 1; https://stacks.cdc.gov/view/cdc/140316). A supplementary analysis estimating VE against all-cause thromboembolic events also indicated a protective effect of bivalent vaccination (Supplementary Table 2; https://stacks.cdc.gov/view/cdc/140315).