Is another bivalent COVID booster shot on the way? Here's what we know.

Last fall, U.S. health officials authorized new COVID-19 booster shots designed to target the original strain of the coronavirus and some of the Omicron subvariants that were circulating around that time. The Centers for Disease Control and Prevention has said that the new booster, known as the bivalent COVID-19 vaccine, offers the highest protection against the virus at the moment.

But uptake has been low. Even though the bivalent booster has been shown to be safe and to increase protection against infection and severe disease, so far only 16% of Americans have received it.

However, many of those who were early adopters of the shots are coming up on six months post-vaccination and are now wondering if they need a second dose, and if so, when.

“This is probably the most common question I get asked: ‘Hey, doc, I got that back in September. It's been a few months. Shouldn't I be getting another booster by now?’” Dr. Peter Hotez, co-director of the Texas Children’s Hospital Center for Vaccine Development and dean of the National School of Tropical Medicine at Baylor College of Medicine, told Yahoo News.

On Tuesday, vaccine advisers in the U.K. recommended a spring booster dose for high-risk groups, including those who are over 75, immunosuppressed or residents of nursing homes.

Many early adopters of the bivalent vaccine don't want to wait until the fall

Federal health agencies such as the Food and Drug Administration and the CDC have not officially made a recommendation on whether a second bivalent booster dose is needed right now. However, the FDA recently proposed switching to an annual COVID-19 booster plan, similar to the flu model. Under this strategy, most healthy people will receive one dose every fall. The agency said some Americans, including older people, unvaccinated young children and those who are immunocompromised, may need to be offered two or more doses a year.

Paula Lazor, 68, from Arlington, Va., told Yahoo News that she and her husband — who is 75 years old and has underlying health conditions — got the bivalent booster as soon as it became available. They’re both now eager to get a second dose.

“My husband and I feel very strongly about getting a second bivalent shot. In fact, we planned to contact our primary care doctor next week … to see if that is possible,” Lazor said, adding that she wants her family to have the highest protection possible against the virus.

The CDC has reaffirmed several times that the primary goal of the country’s COVID-19 vaccination strategy is to prevent severe disease, but people like Lazor also worry about getting "long COVID" and getting others sick.

“We particularly do not want to pass this virus on to our grandchildren,” she said.

Lazor’s concern that the bivalent booster shot’s protection may be waning by now is not unfounded, given what we know about past boosters.

Booster doses were first recommended in the fall of 2021 for high-risk groups. The initial boosters were the same formulation as the primary series, which was designed to target only the original strain of the virus. This is also known as a monovalent vaccine. While these shots proved highly effective at protecting people against severe disease and death, scientific evidence began to show that vaccine effectiveness against COVID-19 hospitalization declined over time. This reduction in protection was significant in particular for those 65 and older. Experts have said the decline in vaccine effectiveness is likely due to a combination of factors, including waning immunity and the emergence of new variants.

“In the past, for the monovalent boosters, when you look at some of the data, the protection against hospitalization starts to fall off after around five months,” Hotez explained. If the bivalent boosters are similar, he said, “we are approaching that time, and that's why I think it's important for the CDC or FDA or both to issue a statement, so we know where we stand at this point.”

Not enough data to make a recommendation right now, CDC says

The CDC’s Advisory Committee on Immunization Practices — a group of outside experts who advise the agency on vaccines — recently met to discuss the COVID-19 shots. During the meeting, the agency presented some data on the effectiveness of the bivalent booster dose.

According to this data, bivalent vaccines continue to offer protection against hospitalizations, but protection against infection seems to wane over time, particularly among older adults. But the agency said, “Waning for bivalent VE [vaccine effectiveness] against hospitalization, including among older adults, isn’t yet known.” This is in part because not enough time has passed since the shot was deployed. At the end of the meeting, the panel of scientists concluded there was “insufficient evidence” available to make a recommendation on whether older adults and those who are immunocompromised need another booster dose at this time. They noted, however, that this can change in the future.

But some experts think federal health agencies should at least authorize the additional booster dose so people have the option to choose for themselves — especially because community transmission continues to be high in many areas of the country, according to CDC data.

At an expert briefing on COVID-19 vaccines recently held by the Johns Hopkins Bloomberg School of Public Health, Dr. William Moss, a professor in the departments of epidemiology and international health as well as molecular microbiology and immunology at that institution, told Yahoo News that authorizing another bivalent booster shot for vulnerable populations would be a sensible idea.

“Officially there’s not a recommendation yet for an additional booster dose for those individuals, but based on what we’ve been saying, I think that would be quite reasonable in vulnerable populations, for whom the last booster was some time ago,” Moss said. “There would have been some waning protective immunity, certainly against mild and perhaps moderate disease. There’s no right answer. It’s also going to depend on the level of community transmission, but I would say that would be a reasonable consideration.”

Dr. Monica Gandhi, an infectious disease specialist and a professor of medicine at the University of California, San Francisco, said it’s understandable that those who are older or immunocompromised feel anxious about not knowing when they can receive another bivalent booster. But she said some studies have shown that the initial doses of the vaccines are still doing a good job at protecting them against severe disease. In addition, she said the COVID antiviral pill Paxlovid continues to be an important tool for those in high-risk groups who catch the virus.

“I would say that the original doses of the vaccines you received seem to be working very well, and I would not worry about needing another dose before the fall, based on the level of evidence that we have,” Gandhi said.