US pharma giant Pfizer's new bivalent mRNA-based Covid booster vaccine has shown to be highly effective in reducing hospitalisation and deaths, particularly in vulnerable patients aged 65 years and above, according to a study published in The Lancet Infectious Diseases.
The bivalent mRNA-vaccines contain elements from both the original wild type Covid strain and an updated component from the Omicron strain.
These vaccines were designed to help improve vaccine-induced immunity against the Omicron variant and subsequent sub variants; and have replaced older style monovalent boosters used in the US, Israel, and other countries since September 2022.
To probe the novel vaccine's effectiveness, a team of Israeli researchers in a study looked at 569,519 people aged 65 years and above between September 27, 2022, and January 25, 2023.
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Of these, 134,215 participants received a bivalent mRNA booster vaccination during the study period.
The team found that those who received the bivalent booster dose had a 72 per cent lower risk of Covid related hospitalisation and a 68 per cent lower risk of Covid related death.
"Bivalent mRNA booster vaccination in adults aged 65 years or older is an effective and essential tool to reduce their risk of hospitalisation and death due to Covid-19. Vaccination remains the primary tool for avoiding severe Covid-19," explains Dr. Ronen Arbel, Community Medical Services Division, Clalit Health Services, Tel Aviv, 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 enhanced protection against severe outcomes," Arbel said.
However, the team acknowledged some limitations of their study, including the low numbers of hospitalisations and deaths, and that use of only the Pfizer bivalent vaccine means that generalisation of the results to other bivalent vaccines should be done with caution.
Also, the study was not a direct comparison between bivalent and monovalent vaccines, since both were not administered at the same time in Israel during the study period.
They also note adverse events are outside the scope of the study, but said that "preliminary short-term safety results published by the CDC have shown a comprehensive safety profile for the bivalent booster and reassured that adverse events reported after a bivalent booster dose are consistent with those reported after monovalent doses."
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"Our results suggest that the bivalent mRNA vaccine booster dose is associated with a reduced risk of severe Covid-19 outcomes in adults aged 65 years or older. Our findings highlight the importance of bivalent booster vaccination in populations at high risk of severe Covid-19 and the necessity to increase efforts to encourage eligible people to be vaccinated," the researchers said.
The findings will also be presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID 2023) to be held in Copenhagen between April 15 and 18.
