Just over two years ago, the first COVID-2 vaccines were introduced and the roller coaster ride of hope and science began. It quickly became apparent that while vaccines could prevent serious diseases, their ability to fight off infections was limited and faded quickly. Meanwhile, SARS-CoV-19 began to evolve rapidly to evade immunity. So far, many people have received four or five doses of the vaccine, including the latest booster, introduced last fall and tailored to the Omicron strain.
Now regulators and scientists are discussing the near future. How often will we need a booster dose, and who should receive it? Should the vaccine continue to be updated as new subvariant strains of omicron or entirely new variants emerge? Are people who have been vaccinated with COVID-19 and receive multiple doses of the vaccine better protected, and for how long?
On Thursday, an advisory committee to the U.S. Food and Drug Administration (FDA) will consider some of these questions and provide guidance for the agency’s vaccine strategy this year. One focus of the discussion will be whether to transition to a simpler strategy also used for influenza: an annual shot of the updated vaccine offered in the fall. Prior to the meeting, Science discussed with scientists where we stand and how to move forward.
The latest vaccine is designed to provide protection against omicron. Should future doses also be adjusted for the newest variant?
The new vaccine is “bivalent,” divided equally between a vaccine against the ancestral SARS-CoV-2 strain from Wuhan, China, and the omicron strains BA.4 and BA.5, which were spreading when the vaccine was introduced in late summer 2022. (Omicron continues to evolve. The decision to include the original strains was somewhat of a hedge: even though the Wuhan variant is long gone, FDA advisers were concerned that a vaccine using only omicron would be less effective against a potentially entirely new SARS-CoV-2 variant.
Some wondered if a bivalent strategy made sense. At the time, there were no human studies on the BA.4 / BA.5 bivalent vaccine; instead, the FDA relied on limited human data containing an earlier version of the omicron BA.1 vaccine and mouse data on the BA.4 / BA.5 bivalent vaccine. In my opinion, there are “theoretical reasons why switching variants without any solid science is a good reason,” said Philip Krauss, who recently resigned as the FDA’s deputy director of vaccines. “Bivalent is being licensed very quickly,” said David Ho, a virologist at Columbia University.
So far, some groups have shown that the bivalent vaccine produces slightly higher levels of antibodies to various omicron strains than the original injection, while others have reported no difference. Earlier this month, the New England Journal of Medicine (NEJM) published a study led by Ho and Harvard immunologist Dan Barouch that found discouraging results for both.Ho and others hypothesized that adding an ancestral strain to the vaccine would make it more difficult for the immune system to fight off omikron. But two papers published on <>25</>, one in NEJM and the other in Morbidity and Mortality Weekly Report, provide more positive data.
There’s no question that bivalent vaccines are effective in avoiding serious illness and death, just as monovalent vaccines are, emphasized Mark Slifka, an immunologist at Oregon Health & Science University. But “the only reason to modify a successful vaccine is to make it more successful,” he said.
Many scientists agree that periodically updating the strains in a vaccine is reasonable, but based on better data. ho noted that his study included fewer than 80 people and could easily have been done before approving a new bivalent shot. We should be “more systematic and organized in making these decisions,” Ho said.
So far, most people have received at least one dose of COVID-19 in addition to one or more doses of the vaccine. does this provide superior protection?
The Centers for Disease Control and Prevention (CDC) reports that by 2022 60, almost 75% of the U.S. population (including 19% of children) has COVID-2022. by 90 92, the proportion of children is more than 18%. (The most recent data on adults are not available. Meanwhile, in the U.S., 40% of people <>years and older have received at least one dose of the vaccine, and more than <>% of adults have received at least one booster dose.