Covid-19 Vaccines for 2023-2024 Campaign should Target Dominant XBB Variant

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The U.S. Food and Drug Administration's (FDA) staff reviewers have recommended that the COVID-19 vaccines being developed and manufactured for the 2023-2024 campaign should target one of the currently dominant XBB variants. This suggestion was made in documents posted ahead of the FDA's independent experts' panel meeting, which is scheduled for Thursday and where recommendations will be made regarding the strain that an updated COVID-19 booster should focus on.

In May, an advisory group to the World Health Organization (WHO) recommended that COVID-19 booster shots for the year should be updated to target XBB subvariants. The previous COVID vaccine boosters in the United States included both the original strain of the vaccine and Omicron in a bivalent shot.

According to CDC data from early May, roughly 17% of Americans had a COVID booster dose during the 2022-2023 immunisation season.

Although COVID-related mortality in the United States increased in January, they have already fallen back, with a 14.3% drop in the last week.

Because the virus is unpredictable, regulators emphasise the importance of updating immunisations. According to the FDA reviewers' recommendations, the COVID vaccination campaign should include a monovalent vaccine targeting either the XBB.1.5, XBB.1.16, or XBB.2.3 variations. They mentioned that XBB subvariants accounted for over 95% of the circulating virus variants in the United States by early June 2023.

Leading COVID-19 vaccine manufacturers such as Pfizer/BioNTech, Moderna Inc, and Novavax Inc are already developing versions of their vaccines targeting XBB.1.5 and other currently circulating strains.

The Food and Drug Administration advisers will convene on Thursday to discuss the necessary updates for the subsequent COVID boosters to target the strains that may circulate in the upcoming fall.

Time is crucial as the FDA needs to select the strain(s) it believes will be prevalent later this year, allowing drugmakers enough time to produce the new shots. This approach mirrors the selection process for the yearly flu shot, where scientists assess the circulating strains and estimate the most prevalent ones to include in the vaccine.

This will be the second time the COVID vaccines have been updated. Last year, the FDA authorized new shots that targeted both the original coronavirus strain and the BA.4 and BA.5 omicron subvariants, which are no longer in circulation in the U.S. The initial vaccines authorized in December 2020 solely targeted the original coronavirus.

FDA experts proposed in briefing documents revealed on Monday that the modified boosters should target at least one of the main XBB types. This strain appeared in October and is the result of two omicron subvariants. Since last autumn, new XBB strains have been appearing.

According to the Centers for Disease Control and Prevention, XBB.1.5 is currently the dominant strain circulating in the United States, accounting for approximately 40% of all new COVID cases. It is followed by XBB.1.16 ("Arcturus" on social media) and XBB.1.9.1, making up around 18% and 12% of all new cases, respectively. The XBB strains have not caused a surge in cases like previous variants.

The FDA scientists stated in the documents that real-world studies indicate that although the currently updated boosters used in the U.S. protect XBB.1.5, the generated antibodies seem to be lower compared to those against BA.4 and BA.5. Therefore, they suggested an updated strain composition of COVID-19 vaccines to more closely match the currently circulating Omicron sublineages for the 2023-2024 vaccination campaign.

If the new vaccines are updated to target some form of XBB, they will align with the recommendations of the World Health Organization. In May, the WHO recommended that the following COVID boosters target XBB subvariants. The European Medicines Agency also supported the WHO's recommendation in June. Notably, countries, including the U.S., generally follow the WHO's guidance for the flu vaccine each year.

The FDA's advisory committee, the Vaccines and Related Biological Products Advisory Committee will determine which specific XBB lineage should be included in the vaccine. The FDA's briefing documents indicate that it is unclear whether the new vaccines will be recommended for everyone in the fall. The CDC's Advisory Committee on Immunization Practices will meet next week to discuss updated COVID boosters, among other vaccines.

Dr. Ofer Levy, director of the Precision Vaccines Programme at Boston Children's Hospital, advised that everyone in the United States get a COVID booster shot every year. He believes it will boost the antibody response and, most likely, benefit T cells as well.

It remains uncertain whether the FDA will require the new vaccines to target the original coronavirus strain, identified in late 2019, and an XBB strain. A vaccine that targets two songs is known as a bivalent vaccine.

Given the significant diversity of the currently circulating strains from the original, Dr. Isaac Bogoch, an infectious disease specialist at the University of Toronto, questions the "added benefit" of putting the original strain in the vaccine.

"It seems like it would make sense to cover XBB," Bogoch added.

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