Effectiveness of Covid-19 Vaccines over a 9-Month Period in North Carolina

Abstract

Background The duration of protection afforded by coronavirus disease 2019 (Covid-19) vaccines in the United States is unclear. Whether the increase in postvaccination infections during the summer of 2021 was caused by declining immunity over time, the emergence of the B.1.617.2 (delta) variant, or both is unknown. Methods We extracted data regarding Covid-19–related vaccination and outcomes during a 9-month period (December 11, 2020, to September 8, 2021) for approximately 10.6 million North Carolina residents by linking data from the North Carolina Covid-19 Surveillance System and the Covid-19 Vaccine Management System. We used a Cox regression model to estimate the effectiveness of the BNT162b2 (Pfizer–BioNTech), mRNA-1273 (Moderna), and Ad26.COV2.S (Johnson & Johnson–Janssen) vaccines in reducing the current risks of Covid-19, hospitalization, and death, as a function of time elapsed since vaccination. Results For the two-dose regimens of messenger RNA (mRNA) vaccines BNT162b2 (30 μg per dose) and mRNA-1273 (100 μg per dose), vaccine effectiveness against Covid-19 was 94.5% (95% confidence interval [CI], 94.1 to 94.9) and 95.9% (95% CI, 95.5 to 96.2), respectively, at 2 months after the first dose and decreased to 66.6% (95% CI, 65.2 to 67.8) and 80.3% (95% CI, 79.3 to 81.2), respectively, at 7 months. Among early recipients of BNT162b2 and mRNA-1273, effectiveness decreased by approximately 15 and 10 percentage points, respectively, from mid-June to mid-July, when the delta variant became dominant. For the one-dose regimen of Ad26.COV2.S (5×10 10 viral particles), effectiveness against Covid-19 was 74.8% (95% CI, 72.5 to 76.9) at 1 month and decreased to 59.4% (95% CI, 57.2 to 61.5) at 5 months. All three vaccines maintained better effectiveness in preventing hospitalization and death than in preventing infection over time, although the two mRNA vaccines provided higher levels of protection than Ad26.COV2.S. Conclusions All three Covid-19 vaccines had durable effectiveness in reducing the risks of hospitalization and death. Waning protection against infection over time was due to both declining immunity and the emergence of the delta variant. (Funded by a Dennis Gillings Distinguished Professorship and the National Institutes of Health.)

Demographic Characteristics and Status of Vaccinated Individuals with a History of COVID-19 Infection Pre- or Post-Vaccination: A Descriptive Study of a Nationally Representative Sample in Saudi Arabia

“…In addition, more than two-thirds of those admitted to ICUs received one injection of a COVID-19 vaccine (Oxford-AstraZeneca or Pfizer-BioNTech). These findings are in accordance with the published literature that reported the effectiveness of vaccines in reducing mortality and the importance of full immunization against COVID-19, which results in lower rates of hospitalization and mortality [47][48][49]. Even though there was no difference in the odds of mortality between the two vaccines (Oxford-AstraZeneca and Pfizer-BioNTech), each one of these vaccines resulted in significant reduction in the odds of mortality, as previously reported [30].…”

Estimating COVID-19 Vaccination Effectiveness Using Electronic Health Records of an Academic Medical Center in Michigan

“…Studies during mid-2021 reported VE of 79.8% 7 and 79.9-98.4% 4 against infection and 95.3% 7 , 86% (CI 82-88%) 5 , 80-97.5% 4 , and 80.0% (CI 76.8-82.7%) 9 against hospitalization across different variants. A recent study that looked further at the waning VE from late 2020 through Q3 of 2021 found VE rates for mRNA vaccines to be the highest two weeks after a two-dose vaccination regimen (94.5%; CI 94.1-94.9%), lining up with our estimates of VE in Q2, and lowest at 66.6% (CI 65.2-67.8%) after seven months 8 , which corresponds with our VE estimates in Q3. Taken together, these results highlight the need for appropriate adjustment for patient covariates, timing of vaccination, booster status, and for replication across different regions and time periods to more fully understand VE and potential VE modifying factors.…”

Breakthrough infections after COVID-19 vaccination: Insights, perspectives and challenges

“…The drop of anti-Spike IgG levels is apparent as early as 70 days after the completion of a full vaccination scheme, with a two- and five-fold reduction compared with the levels at 20–40 days for BNT162b2 and ChAdOx1 recipients, respectively [ 36 ]. Given that there is a parallel trend regarding neutralizing antibody titers [ 35 ], which may serve as a surrogate of immunity against SARS-CoV-2 [ 37 ], this humoral phenomenon coincides with a gradually increasing susceptibility of fully vaccinated individuals for breakthrough infections in the months following immunization [ [38] , [39] , [40] , [41] ]. As immunity diminishes over time, the most notable decreases in vaccine effectiveness have occurred in milder forms and asymptomatic infections, in those vaccinated earliest, in older subjects and in those infected with the Omicron variant [ 15 , 23 ].…”