CNN  — 

Even though the biopharmaceutical company Pfizer has announced that it might be time to consider giving a third dose of its coronavirus vaccine to people, many doctors and public health officials argue that it’s more beneficial to get shots into the arms of the unvaccinated right now than to boost those who are already fully vaccinated.

“It’s wonderful to have a booster approved for emergency use authorization on the shelf – ready to go any time we need it. But I do not think we need it right now,” Dr. William Schaffner, a professor at Vanderbilt University School of Medicine and medical director of the National Foundation for Infectious Diseases, told CNN on Friday.

On Thursday, the companies Pfizer and BioNTech announced that a third dose of their coronavirus vaccine, given six months after a second dose, appears to preserve “the highest levels of protection” in those who were vaccinated.

The companies made their announcement without releasing any new data, but noted plans to publish new information soon. A Pfizer spokesperson later told CNN that the company plans to file for emergency use authorization for a booster dose with the US Food and Drug Administration in August.

Just hours after the Pfizer/BioNTech announcement was made, the FDA and US Centers for Disease Control and Prevention pushed back in an unprecedented joint statement emphasizing that people who are fully vaccinated “do not need a booster shot at this time” and people who are unvaccinated should “get vaccinated as soon as possible to protect themselves and their community.”

The statement also said, “We are prepared for booster doses if and when the science demonstrates that they are needed.”

But that science is unclear, and there is still much to learn about the potential need for booster doses of coronavirus vaccine.

“We respect what the pharmaceutical company is doing, but the American public should take their advice from the CDC and the FDA,” National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci told CNN on Friday. “The message is very clear: the CDC and the FDA say if you have been fully vaccinated at this point in time, you do not need a booster shot.”

Here is what we do and don’t know.

Known – vaccines still work, even against variants

Vaccine makers are looking ahead at what might be needed in the future while public health officials are focused on the present need for vaccinations, Dr. Jerome Adams, former US surgeon general under the Trump administration, told CNN’s John Berman on Friday morning.

“The companies are thinking about where the hockey puck is going,” Adams said during an appearance on New Day. “Whereas the government, FDA and CDC, are looking at where the hockey puck is right now. They want to reassure Americans your best protection still is a vaccine, and you still have great protection – better than for the flu shot in any given year – even in the face of variants and waning immunity.”

Some real-world evidence of waning immunity with Pfizer’s coronavirus vaccine has emerged in Israel, where the Ministry of Health issued a brief statement Monday saying an analysis had shown the coronavirus vaccine was somewhat less protective against severe disease than before, and linked this change to the spread of the Delta variant, a more transmissible and possibly more dangerous strain of coronavirus.

The Israeli government’s statement said that as of June 6, the vaccine provided 64% protection against all infections, including asymptomatic infection and mild disease, and 93% efficacy in preventing severe disease and hospitalizations.

When it comes to whether booster doses might be needed to help protect people against emerging coronavirus variants specifically, Schaffner said that the Pfizer vaccine and others already have been shown to still offer some protection.

“It’s really unusual for a vaccinated person to be admitted to the hospital today for Covid-related illness, reinforcing the notion that these vaccines are still working against the variants,” Schaffner said. The Delta variant now makes up more than half of all new Covid-19 infections in the United States, according to estimates from the CDC.

Overall, since protection from the vaccine against severe Covid-19 still remains high, Schaffner said that fully vaccinated people should not worry.

“Protection against hospitalization and intensive care unit admission and dying continues – and so, those antibodies that are produced by the vaccine are really still providing very solid protection for persons who have received the vaccine,” Schaffner said, adding that he is fully vaccinated with the Pfizer vaccine.

“We had hoped that the vaccines could protect not only against serious disease, but our getting infected. They do have some impact in diminishing our chance of getting infected,” he added. “It’s not as good as we had hoped, but that’s less important, because the main goal of the vaccine was to keep us out of the hospital, and vaccines continue to do that very well.”

Unknown – when we will need third doses of vaccine

Experts say more data is needed to decide on whether people might eventually need booster doses of Covid-19 vaccines.

A rise in so-called breakthrough cases might offer a clue in the future, federal vaccine advisers said during a meeting in June. A “breakthrough” infection refers to Covid-19 cases that occur after someone has been fully vaccinated.

Members of the CDC’s Advisory Committee on Immunization Practices discussed in a meeting last month when it might be time for the agency to make recommendations for booster doses of vaccine.

Committee members mostly agreed that more data around the benefits of boosters is needed – but a rise in “breakthrough” infections could be a sign in the future that immunity is waning and it’s time to reevaluate the need for boosters.

“I think the only thing we can do at this moment is, if we start to see an uptick in reinfections in people, or new infections in people who have been vaccinated, that’s our clue that we need to move quickly,” ACIP member Dr. Sharon Frey, who is a vaccine specialist at St Louis University Medical School, said in last month’s meeting.

In general, “what we are looking for is both a very careful look at breakthrough cases and also whether there is currently an uptick in the elderly – that would be pretty clear because they are currently so well controlled,” said ACIP member Dr. Sarah Long, a professor of pediatrics at Drexel University College of Medicine.

“It would be a mistake to be giving booster doses without both some information about number one: Do they boost? And a little bit of safety data,” Long said. “So that we would have some idea that there would be benefit of the booster before we might incur unknown risk.”

Known – some people might benefit more from a boost than others

In the future, there are some people who might benefit from booster doses of coronavirus vaccine more than others, including those who are immunocompromised. Schaffner said patients who fall into the category represent between 2% and 4% of the US population.

For instance, organ transplant recipients might not have an adequate response to coronavirus vaccines because they take drugs to suppress their immune systems. That helps reduce the risk of the body rejecting new organs but may also limit responses to vaccines.

A third dose of coronavirus vaccine could help boost antibody levels among some organ transplant recipients who have not had robust responses to the standard vaccination schedules, according to a study published in the journal Annals of Internal Medicine in June.

Among patients in the study who had no measurable antibodies after receiving two doses of vaccine, one-third of them saw a rise in antibodies after a third dose – and among those with low antibody levels after two doses, all of them saw an increase after a third dose.

But there’s not much data on vaccinations in immunocompromised people because when pharmaceutical companies tested coronavirus vaccines in clinical trials last year, they specifically excluded people who were taking immunosuppressive drugs due to potential risks.

In last month’s meeting, the CDC’s ACIP panel discussed this and the high-risk groups of people – immunocompromised patients, long-term care facility residents, older adults, and health care personnel – who may benefit from booster doses more than the general public.

“I have personally seen people die well after two full doses of mRNA vaccine because, we believe, they were immunocompromised and didn’t have full protection,” said ACIP member Dr. Camille Kotton, who cares for immunocompromised patients at Massachusetts General Hospital and Harvard Medical School.

“So, for me, this is the next important frontier that we really need to deal with and as rapidly as possible,” Kotton said about booster doses.

Kotton encouraged her colleagues on the committee to consider proceeding with recommendations for booster shots “as soon as we have good science” available on which to base decisions.

“I would wait for the additional data to be available, including the safety data as well,” Kotton said, adding, “This is a hot topic.”

Known – vaccine makers will seek full approval soon

There are three coronavirus vaccines authorized for emergency use in the United States: the two-dose Pfizer/BioNTech vaccine for ages 12 and older, and the two-dose Moderna vaccine and one-dose Johnson & Johnson vaccine for ages 18 and older.

The companies Pfizer/BioNTech and Moderna have begun their applications to receive full FDA approval to use their vaccines and Johnson & Johnson has said it intends to file an application but has not yet done so.

To get more people vaccinated against Covid-19, it could be beneficial for the FDA to consider approving Pfizer’s vaccine before authorizing a booster shot, Dr. Carlos del Rio, executive associate dean at Emory University School of Medicine, told CNN on Friday. He added that he received the Pfizer vaccine in December and is not “running to find a booster” right now.

“The most important thing for the FDA to do right now is not to consider a Pfizer request for a booster shot. It’s actually to get full FDA approval for the vaccine, because that will change the dynamic,” del Rio said, adding that it will be easier to get more people vaccinated.

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Due to the seriousness of the pandemic, vaccine makers originally applied for EUAs because the authorization process takes less time than what would be required for full approval. Emergency use authorization is what its name suggests – a medical product, such as a vaccine, that gets special FDA authorization to be used during an emergency.

Progressing from authorized to approved would allow manufacturers to market and directly distribute their vaccines. It could also have an impact on vaccine mandates – and perhaps sway skeptics hesitant to get the vaccines now.

“I’m worried about the fact that the FDA quite frankly hasn’t yet given us an update on full approval of these vaccines, which we know is causing hesitancy in many people and which also is causing companies and businesses and schools to delay their decisions about vaccine mandates,” Adams said.