Efficacy of XBB.1.5 COVID-19 Vaccines Decline Over Time, Study Finds

United States: The latest iteration of the monovalent XBB.1.5 COVID-19 vaccines demonstrated efficacy against the circulating Omicron subvariants during the recent respiratory virus season, though their potency diminished over time, as indicated by a concise report.

The trio of vaccines, updated to combat the SARS-CoV-2 XBB.1.5 subvariant—namely, Moderna’s, Pfizer-BioNTech’s mRNA vaccines, and the Novavax vaccine—exhibited a 66.8% efficacy against hospitalization at the four-week mark, which decreased to 57.1% by ten weeks, detailed Dan-Yu Lin, PhD, from the UNC Gillings School of Global Public Health, and his collaborators.

Efficacy against infection stood at approximately 52% after four weeks, waning to 33% after ten weeks, and further declining to 20% at the twenty-week mark, as shown in correspondence in the New England Journal of Medicine, according to Medpage Today.

“We anticipated these vaccines would be efficacious, particularly in preventing hospitalizations and fatalities. We also foresaw a decline in effectiveness over time,” Lin conveyed to MedPage Today. “However, the precise levels of efficacy and duration of protection were unknown to us beforehand.”

Although the protection against mortality was higher—72% after four weeks and 61.4% after ten weeks than that against infection or hospitalization, the authors noted “considerable uncertainty” due to the low number of deaths in the study cohort.

The data suggested reduced efficacy against infection, hospitalization, and death with the emergence of the JN.1 subvariant, which became the predominant strain in the US by the end of March of this year.

For individuals vaccinated prior to October 26, 2023—before the JN.1 variant’s predominance—the vaccines were 64.4% effective against infection after four weeks, decreasing to 40.9% after ten weeks and 22.4% after eighteen weeks. Conversely, for those vaccinated between October 26, 2023, and February 10, 2024—during JN.1’s dominance—vaccine efficacy against infection was 44.3% after four weeks, dropping to 17.4% after ten weeks.

In the pre-JN.1 period, effectiveness against hospitalization was 73.7% after eight weeks and 59.1% after ten weeks, while effectiveness against mortality was 86.2% at week four and 72.9% at week eight. Among those vaccinated post-JN.1’s emergence, effectiveness against hospitalization was 60.1% after four weeks, with mortality protection at 59.8% after four weeks, both declining progressively over time, as highlighted by MedPage Today.

“It would be prudent to develop and deploy new vaccines targeting JN.1 or future variants,” the authors suggested.

The FDA’s Vaccines and Related Biological Products Advisory Committee is scheduled to meet on June 5 to discuss and vote on the format of the influenza vaccine for the next two seasons 2024-2025. Indications are that JN.1 or one of its more recent off springs such as KP. 2, which currently accounts for an estimated 29% of US cases, will be the one selected.

In September this year, the World Health Organization (WHO) Technical Advisory Group on COVID-19 Vaccine Composition suggested that the subsequent generation of COVID-19 vaccines should be of JN. 1 lineage as the antigen for future formulations will be recommended. The FDA was in a position to follow WHO’s recommendations last year by choosing an XBB. 1-based strain, endorsing the monovalent XBB. 1. Five-targeted mRNA vaccines by September of 2023.

Further analyses from Lin’s team revealed that the XBB.1.5 vaccines were effective across various age demographics and among individuals who had neither been previously infected nor vaccinated. Lin remarked that the durability of these vaccines “was broadly consistent with our earlier findings on the longevity of bivalent boosters against BQ.1-BQ.1.1 and XBB-XBB.1.5.3,” as per MedPage Today.

For their research, the scientists utilized data on vaccine uptake from the Nebraska Electronic Disease Surveillance System and the Nebraska State Immunization Information System. They scrutinized all hospital discharge data from the Nebraska Hospital Association and reviewed all death certificates in Nebraska to identify COVID-19-related deaths.

In a cohort of 1.8 million individuals, 218,250 received one of the XBB.1.5 vaccines between September 11, 2023, and February 21, 2024. Of those vaccinated, 61.1% received the Pfizer-BioNTech vaccine, and 38.6% received the Moderna vaccine.

The primary outcomes examined were COVID-19 infection, hospitalization, hospitalization or death (whichever occurred first), and death. During the study period, there were 21,988 reported SARS-CoV-2 infections, 1,364 COVID-related hospitalizations, and 237 COVID-related deaths.

The study did not incorporate results from at-home COVID-19 antigen tests.

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