A fourth dose of the bivalent COVID-19 vaccine has been found to offer significant protection against hospitalization, according to an observational study published in The Lancet Infectious Diseases. The study compared the effectiveness of a fourth dose of the bivalent or monovalent COVID-19 vaccine in preventing medical treatment and hospitalization among 2,749,819 adults in Singapore.
The majority of participants had previously received three monovalent doses and were eligible for a fourth dose. The study found that a fourth dose of the bivalent vaccine was substantially more effective in preventing medical treatment and hospitalization than a fourth dose of the monovalent vaccine, regardless of whether the individuals had previously been infected with COVID-19 or not.
The monovalent vaccine targets the wild-type strain of the SARS-CoV-2 virus, while the bivalent vaccine targets both the wild-type strain and the Omicron variant. The study revealed that a fourth monovalent dose did not provide additional protection against symptomatic infection among individuals who had not been previously infected. However, a fourth dose of the bivalent vaccine offered significant protection, with an 82% reduction in the risk of symptomatic infection.
Furthermore, the study showed that four doses of the bivalent vaccine provided greater protection against hospitalization than four doses of the monovalent vaccine, regardless of previous infection status. The bivalent vaccine was found to be more effective than the monovalent vaccine in preventing hospitalization among both previously infected and never-infected individuals.
Importantly, the study found no evidence of waning effectiveness of the bivalent vaccine against medical treatment after two months, indicating its long-term efficacy. Additionally, the bivalent Pfizer vaccine targeting the BA.4/BA.5 subvariant of the Omicron variant was found to be more effective than the Moderna version, which targets the BA.1 subvariant.
Based on these findings, the study authors recommend considering boosters with an omicron-adapted bivalent mRNA vaccine to provide additional protection against emerging Omicron variants, even in populations with high levels of hybrid immunity.
In response to the study, Ronen Arbel, PhD, and Yael Wolff-Sagy, PhD, both of Clalit Health Services in Israel, emphasized the importance of the study’s findings for COVID-19 vaccine policies. They suggested that countries should consider discontinuing the use of monovalent vaccines and continue vaccinating young adults and individuals with hybrid immunity, as preventing medically attended symptomatic SARS-CoV-2 infections remains crucial.
In conclusion, the study highlights the substantial benefits of a fourth dose of the bivalent COVID-19 vaccine in preventing hospitalization and medical treatment. These findings support the recommendation of boosters with an omicron-adapted bivalent mRNA vaccine for enhanced protection against emerging Omicron variants. As vaccine policies continue to evolve, the focus remains on preventing symptomatic infections and providing effective healthcare support.
