Two new studies suggested that the bivalent Pfizer/BioNTech mRNA COVID-19 vaccine offered children and adolescents good protection against severe outcomes brought on by the Delta and Omicron strains of COVID-19. The bivalent vaccine was replaced with a monovalent vaccine in fall 2023.
Researchers from the University of Pennsylvania and Children’s Hospital of Philadelphia (CHOP) analyzed the effectiveness of the vaccine against infection among 250,000 never-infected COVID-19 patients at various pediatric health systems. Around half of the participants, who were all between the ages of 5 and 20, had received at least one dose of the Pfizer vaccine sometime during the Delta and Omicron waves beginning in mid-2021 and 2022, respectively.
The study, published in the Annals of Internal Medicine, determined that estimated vaccine effectiveness (VE) was “98.4% against infection among adolescents” between the ages of 12 and 20 during Delta, with “no significant waning after the first dose and no significant difference in cardiac complications between vaccinated and unvaccinated groups.”
Then, during Omicron, estimated VE in children aged 5 to 11 was 74.3% compared to 85.5% in adolescents. However, VE did wane about 4 months after dose one before leveling off. Among children, there was increased VE against moderate or severe illness (75.5%) and intensive care unit admission (84.9%). In adolescents, estimated VE against moderate or severe illness was 84.8% and 91.5% against ICU admission.
The study authors concluded that the vaccine has a “pivotal role in reducing SARS-CoV-2 transmission, minimizing COVID-19-related sick leaves, and alleviating economic burdens during the pandemic.” Co-senior study author Christopher Forrest, MD, PhD, of UPenn and CHOP, urges that “more information is needed on effectiveness of vaccination delivered to children and adolescents during recent time periods.”
A separate study published in Cell saw Ohio State University researchers analyze “neutralizing antibodies in serum samples from healthcare providers who received three monovalent vaccine doses or two monovalent doses followed by a bivalent booster and from first responders infected with COVID-19 during the Omicron XBB.1.5 wave. They compared the ability of neutralizing antibodies to prevent infection by BA.2.86 [which is the ancestor of the currently dominant Omicron JN.1 variant], the FLip XBB-derived variant, the wild-type virus, and several other variants.” Bivalent vaccine-induced serum antibodies were more efficient at neutralizing BA.2.86 than other Omicron variants, but monovalent vaccines (and previous XBB.1.5 infection) were only marginally effective in preventing BA.2.86 infection.
Senior study author Shan-Lu Liu, MD, PhD of Ohio State, said in a news release that “antibodies generated by infection are low – almost 10-fold lower than vaccine-induced antibodies. That is why you cannot rely on natural infection alone for immunity.” Liu also recommended getting a booster since the bivalent COVID-19 vaccine is less effective against BA.2.86 than the currently available monovalent booster.
CIDRAP has the news release on the two studies.