Vaccine Strategy for Winter: Targeting the FDA JN.1 Strain or Its Offspring
As the number of Covid-19 cases in the United States remains low, vaccine scientists are already strategizing to prevent a seasonal increase in the coming winter. A panel of experts who advise the Food and Drug Administration (FDA) unanimously recommended updating the Covid vaccine scheduled for autumn to target the highly contagious FDA JN.1 strain or one of its offspring.
The FDA JN.1 strain appeared in late August in the United States and became the most prevalent strain by January. It was followed by the emergence of several offshoots, including KP.1.1 and KP.2, which are known as FLiRT variations. In mid-May, KP.2 became the predominant strain in the United States, surpassing JN.1, as reported by the Centers for Disease Control and Prevention (CDC). The FDA states that over one in four new infections are caused by this strain.
During a conference on Wednesday, Natalie Thornburg, a research microbiologist at the CDC, noted that the FDA Coronavirus seems to follow a predictable pattern. She explained that in early winter, a dominant strain known as the “parent” strain gains ground, and by spring, a few progeny begin to appear. This behavior was observed in the XBB strain from the previous year as well. It dominated during the winter but generated offshoots in the spring.
The panel’s recommendation did not specify whether to include the “parent” JN.1 strain or one of its progeny, although most panel members expressed a preference for JN.1. Dr. Bruce Gellin, the chief of global public health strategy at the Rockefeller Foundation and a panel member, suggested maintaining the current course of action after the vote.
Dr. Peter Marks, the FDA’s chief vaccine regulator, urged the committee to consider one of the more recent strains, such as KP.2. He emphasized the rapidity with which new mRNA-based vaccination shots can be created and delivered. Marks questioned whether they would regret not being closer to the more recent strains.
The FDA will soon determine which strain manufacturers should focus on to develop the revised dosage for the autumn vaccination program. Pfizer announced that it could distribute the enhanced Covid vaccines immediately upon FDA approval, while Moderna indicated that it could start distributing the doses as early as mid-August.
Novavax is also working on plans to introduce an enhanced vaccination specifically targeting JN.1 in August. However, the company mentioned that if the FDA selects Novavax’s protein-based vaccine, it will not have an updated vaccine available for the autumn immunization program because it requires a lengthier manufacturing time compared to Pfizer and Moderna, which are based on mRNA.
According to data provided by all three drugmakers, the most recent vaccination targeting the now-extinct subvariant XBB.1.5 is expected to produce a lower number of antibodies against circulating strains of the virus than the JN.1 vaccine. The older vaccine will be phased out upon the release of the upgraded version.
Despite indications that the number of cases may be on the upward trend, hospitalizations for Covid-19 remain at their lowest levels since the pandemic began in 2020. CDC data shows that as of May 25, the weekly test positivity rate has increased from 3.4% to 4.2%. However, it was nearly 30% in early 2022 when the Omicron variant rapidly spread.
Thornburg believes that nearly everyone has acquired immunity to Covid-19 through vaccination, infection, or a combination of both. She stated that they are currently at a seroprevalence of approximately 95%, which indicates the percentage of the population that has been exposed to the virus.
The CDC advisory council is expected to issue recommendations later this month regarding the eligibility of the vaccination for autumn administration.