When the COVID-19 pandemic was officially declared on March 11, 2020, very little was understood about the virus, how it spread, and when we could expect any sort of preventative treatment to be available. However, with the late 2020 approval of two vaccines from Pfizer and Moderna as a two-dose series—as well as the single-dose option from Johnson&Johnson—there was plenty of hope on the horizon. Those vaccines are still working, but there are increasing concerns that major changes may be essential.
Booster doses have also been approved to help sustain vaccines' protective power, but scientists have expressed a need to understand how new and evolving variants and waves of disease impact the ongoing effectiveness of vaccines. According to a pre-release of an April 6 briefing from the U.S. Food and Drug Administration (FDA), these mutations occur rapidly, especially when using an immunocompromised person as a host. When this is combined with varying transmission rates and a large number of people infected, it becomes that much more difficult for experts to predict COVID's evolution.
To account for emerging strains, the current COVID vaccines may need to be updated to ensure effectiveness, according to the FDA briefing. The question will be addressed in the Vaccines and Related Biological Products Advisory Committee meeting slated April 6.
"Although a complete understanding of how emerging SARS-CoV-2 variants impact the effectiveness of current COVID-19 vaccines is lacking, the accumulating data suggest that the composition of vaccines may need to be updated at some point to ensure the high level of efficacy demonstrated in the early vaccine clinical trials," the FDA briefing reads.
In addition to discussing the "optimal strain composition" of the COVID vaccines, virus experts will also discuss how frequently strain changes need to be evaluated, how to implement a formal process for vaccine strain selection, as well as the ideal timing for booster doses within the general population and specific subpopulations.
As reported by CNBC and noted in the FDA briefing, the vaccines currently being administered were developed to target the spike protein (what allows the virus to invade target cells) from the original coronavirus strain, which emerged in 2019. Researchers are seeking a better understanding of how new COVID variants affect vaccine effectiveness, as observational research studies have suggested a decrease in response, particularly to the current dominant variant, Omicron, the FDA said.
While booster shots for both the Moderna and Pfizer vaccines were able to restore waning effectiveness against severe disease and hospitalization as a result of Omicron, the effects have been shown to dissipate over time, providing less protection against mild disease or even hospitalization, the FDA reports. This is also a pressing concern for those who are immunocompromised.
According to a Feb. 18 briefing from the Centers for Disease Control and Prevention (CDC), protection against COVID after two doses of an mRNA vaccine, namely Moderna and Pfizer, wanes over time. When looking at effectiveness after a third dose during the Omicron-predominant period, protection against visits to the emergency department or urgent care declined from 87 percent at two months to 66 percent at four months. Effectiveness against COVID-related hospitalizations also declined from 91 percent at two months to 78 percent at four months.
Experts are also uncertain about how long certain variants will stay dominant, which further complicates the issue of modifying vaccines and how often. To address questions, the FDA suggested referencing the "well-defined process" used to update season flu vaccines.
The World Health Organization (WHO) meets twice annually to discuss flu variants and make a recommendation, and the FDA committee makes its own recommendations for the U.S., the document states. While the two entities normally have the same recommendations, according to CNBC, a COVID vaccine update may be done without a WHO recommendation.
In its briefing, the FDA discussed the potential of a multivalent vaccine, which would target multiple spike proteins from different COVID variants. This could offer benefits over a monovalent vaccine, which targets just one variant; however, any changes to vaccines will need to be supported by data from clinical trials, ensuring safety and efficacy, before they can be authorized by the FDA.