Since September 2022, bivalent mRNA vaccines, containing elements of the original wild-type COVID strain and an updated component of the Omicron strain, have replaced older-style monovalent boosters in the US, Israel and other countries. These vaccines were designed to help improve vaccine-induced immunity against the omicron variant and subsequent subvariants.
A new study published in The Lancet Infectious Diseases and presented at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID 2023, Copenhagen April 15-18) is one of the first to evaluate the effectiveness of this new type of COVID-19 vaccine. 19 in vulnerable people. people aged 65 and over. The study evaluated the bivalent Pfizer vaccine, as Pfizer is the main supplier of COVID vaccines to Israel.
The study shows that, compared to people in this age group who were eligible to receive this bivalent booster but did not receive it , those who received it had a 72% lower risk of COVID-19-related hospitalization and a 68% lower risk of death related to COVID-19 .
“Booster vaccination with bivalent mRNA in adults aged 65 years and older is an effective and essential tool to reduce the risk of hospitalization and death from COVID-19. “Vaccination remains the main tool to prevent severe COVID-19,” explains study co-author Dr. Ronen Arbel, Division of Community Medical Services, Clalit Health Services, Tel Aviv, and the Maximization Research Laboratory. of Health Outcomes, Sapir College, Sderot, Israel. “Our findings highlight the importance of new types of vaccines containing different variants of SARS-CoV-2, which are likely to induce broader immune responses and provide greater protection against severe outcomes.”
To date, there are no randomized controlled trials evaluating the clinical efficacy of a bivalent mRNA booster vaccine. Bivalent mRNA booster vaccines are currently prioritized in Israel for people at high risk of severe COVID-19, primarily those aged 65 and older. This made it possible for the authors to conduct a retrospective cohort study to evaluate the effectiveness of a booster dose of the bivalent mRNA vaccine in preventing COVID-19 hospitalizations and deaths.
Between September 27, 2022 and January 25, 2023, 569,519 eligible participants were identified. Of these, 134,215 (24%) participants received a bivalent mRNA booster vaccine during the study period. Hospitalization due to COVID-19 occurred in 32 participants who received a bivalent mRNA booster vaccine and 541 who did not receive a bivalent booster vaccine (with analysis showing this means a 72% reduction in the risk of hospitalization for those who receive bivalent reinforcement).
The adjusted risk of Covid-19 hospitalizations in recipients of the bivalent mRNA booster was 0.035% versus 0.124% in non-recipients. Therefore, the absolute risk reduction of COVID-19 hospitalizations was 0.089%, so one COVID-19 hospitalization was avoided for every 1,118 people vaccinated.
The adjusted risk of death from Covid-19 was 0.013% in recipients of the bivalent mRNA booster versus 0.040% in non-recipients, meaning a relative risk reduction of death of 68% for recipients of the bivalent vaccine . The absolute reduction in the risk of death was 0.027%, so one death from COVID-19 was avoided for every 3,722 people vaccinated.
The authors point out some limitations of their study, including the low number of hospitalizations and deaths, and that the exclusive use of the Pfizer bivalent vaccine means that generalizing the results to other bivalent vaccines should be done with caution. Additionally, the study was not a direct comparison between bivalent and monovalent vaccines, as both were not administered at the same time in Israel during the study period.
They also note that adverse events are outside the scope of the study, but note that "preliminary short-term safety results published by the CDC have shown a comprehensive safety profile for the bivalent booster and were reassuring that the adverse events reported after a bivalent booster doses are consistent." with those reported after monovalent doses.”
The authors conclude: “Our results suggest that the booster dose of the bivalent mRNA vaccine is associated with a reduced risk of severe COVID-19 outcomes in adults aged 65 years and older. “Our findings highlight the importance of bivalent booster vaccination in populations at high risk for severe COVID-19 and the need to increase efforts to encourage eligible people to get vaccinated.”
Interpretation Participants who received a booster dose of the bivalent mRNA vaccine had lower rates of hospitalization due to COVID-19 than participants who did not receive a bivalent booster vaccine, up to 120 days after vaccination. These findings highlight the importance of bivalent mRNA booster vaccination in populations at high risk for severe COVID-19. Additional studies with longer observation times are warranted. |
