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When and how will we know if we need Covid-19 booster shots?

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There’s a lot we don’t yet know about the data behind Pfizer and BioNTech’s renewed push to change its two-shot Covid vaccination series to a three-shot regimen. But as the sides bicker about whether a third shot is going to be needed, one thing is certain: The final decision will not rest with the company.

Public health officials, not pharmaceutical executives, will be making the final call on when and whether booster shots will be needed. Pfizer and other manufacturers will surely try to push for approvals; Moderna is already testing a Delta-variant-specific booster. Depending on how their conversations go with vaccine regulators at the Food and Drug Administration, companies may apply for a change to their emergency use authorizations (or to the vaccine license, if they secure one before applying to change their vaccine label to a three-dose one).

But unless the FDA agrees to the change, and unless the Centers for Disease Control and Prevention recommends use of an additional booster — in some or all of the people who got the Pfizer shot — this will remain a two-dose vaccine.

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Anthony Fauci, President Biden’s Covid adviser, made that clear after a Monday meeting with Pfizer, where the company briefed key administration advisers on its as-yet-unpublished data. The company has said the data show that “a third dose may be needed within 6 to 12 months after full vaccination.”

Fauci said that anyone who thinks a decision on booster shots is imminent isn’t reading the situation correctly.

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“As [FDA acting commissioner] Janet Woodcock reminded everyone, we’re talking about issues that are regulatory issues and public health recommendation issues and Advisory Committee on Immunization Practices issues,” Fauci told STAT. “We’re a long way from that.”

“People are jumping the gun here.”

Pfizer has said explicitly that it’s ready to work with regulatory agencies and let scientific data guide the next steps — a point it made clear, again, in a statement after that Monday meeting. “Both Pfizer and the U.S. government share a sense of urgency in staying ahead of the virus that causes Covid-19, and we also agree that the scientific data will dictate next steps in the rigorous regulatory process that we always follow,” the company said.

Fauci, director of the National Institute of Allergy and Infectious Diseases, said the meeting was a courtesy discussion about the data. He would not comment on the results, saying they were shared confidentially.

Deciding to add a third shot to the Pfizer series comes with all sorts of other opportunity costs, too — including further delaying access to vaccine for low- and middle-income countries. The director-general of the World Health Organization, Tedros Adhanom Ghebreyesus, was highly critical Monday of Pfizer’s push for boosters, stressing health workers and older adults in countries without access to vaccine must be a higher priority than people who are already fully vaccinated.

“There are scientific issues. There are ethical issues,” said John Moore, an immunologist at Weill Cornell Medicine. “What is the priority? In America, at the moment, it’s getting doses 1 and 2 out to as many people as possible, particularly in undervaccinated regions. … And a booster for people who got their vaccine less than six months ago doesn’t seem to be on the same degree of urgency.”

Then there’s the question of how to pay for it. The U.S. has already spent billions of dollars on acquiring mRNA vaccines: So far, it’s bought 500 million doses from Moderna and another 300 million from the Pfizer-BioNTech partnership, with options for more. It’s not clear whether the administration and pandemic-response agencies like BARDA can buy the additional doses without cash from Congress. Practically, there’s little chance that Capitol Hill would refuse to fund the extra vaccine doses — it’s just a question of whether formally approving the new spending could pose an unnecessary delay.

“[W]e want to have maximum optionality, including depending on what is most effective with children under the age of 12, including if there is a booster shot needed,” Jen Psaki, the White House press secretary, said on Monday. “So that certainly has long been in our planning, even in advance of knowing whether that will be a recommendation made by our health experts.”

Moore said all experts he has spoken to believe people may need additional Covid shots later. “Nobody is saying ‘never,’” he said. But the decision will need solid science behind it.

“Public policy should not be determined by pharmaceutical companies. They need to be determined by CDC, FDA, NIH — all of the science and health specialists available in the Biden administration.”

Below, we lay out how we got here and the implications of a booster decision.

What do we know about Pfizer’s data so far? 

Pfizer and BioNTech’s doozy of an announcement last week said that data from the Israel Ministry of Health showing that vaccine efficacy declined six months post-vaccination was “consistent with an ongoing analysis” from their own Phase 3 studies — the ones that justified the approval of the vaccine.

The crucial Phase 3 data that support that conclusion — and the company’s push for a third booster — have not yet been made public in any other way. Pfizer has since said that it has submitted that data to a medical journal, but it’s not clear when that will be published. “We’re still finalizing our plans to share the data including whether or not we’ll issue [them] on the preprint server,” a Pfizer spokesperson said.

Why is the Biden administration pushing back on the idea of boosters? 

Federal agencies rushed to dismiss Pfizer’s conclusions. In a rare joint statement last week, the Food and Drug Administration and the Centers for Disease Control and Prevention emphasized that fully vaccinated Americans “do not need a booster shot at this time.” And during a briefing on Monday, Psaki also stressed that Pfizer’s surprise announcement might not have much bearing on U.S. vaccination policy — especially not immediately.

Still, the Biden administration isn’t pushing back on the idea of booster shots so much as it’s pushing back on Pfizer’s acting as a messenger of public health guidance. Psaki stressed Monday that the U.S. makes policy decisions after “holistically” examining data, not in response to a single company’s claims.

There might be a more pressing concern, too: vaccine hesitancy. Already, the Biden administration’s vaccination campaign has hit a wall, and any discussion that makes Americans more nervous about finally getting immunized would be poorly timed. Premature speculation about booster shots would fit the bill: Focus groups conducted by the pollster Frank Luntz have shown that some people are less likely to be vaccinated when they’re told they might need another shot months later.

Does this mean Pfizer and the Biden administration are fighting? 

Probably more about the way this information is coming out, not the process itself. On CNN, Fauci said that Albert Bourla, the CEO of Pfizer, had given him a call to apologize for not giving the government a heads-up. “We are on the same page,” Fauci said. He also called Bourla “a really great guy.”

Pfizer has been saying it expects boosters might be needed from the beginning. The strategy of using a third vaccine dose was announced by Pfizer and BioNTech in February. At that time, the company started the clinical trials referenced in its press release. Part of the reason could be that drug companies hope that there will be a booster market in the future. But they also are likely worried about what happens if boosters are needed and they didn’t develop them. It’s not surprising, given that Pfizer conducted trials of a booster, that the next step is to file that data with the FDA and to meet with the CDC.

Because of rules designed to make sure investors find out about important news, drug companies are used to flagging newsworthy clinical results in short press releases and revealing full data early. Here, that habit is rubbing public health experts and government experts the wrong way.

How much of this is being driven by concerns about the Delta variant?

There are two key scenarios that could determine whether and when people need Covid-19 vaccine boosters: one, if vaccine-generated immunity just generally wanes over time (which could happen in some groups, such as older adults, faster than others), or two, if a variant emerges that can “escape” that elicited immune response in ways that render the vaccines less effective. Companies have been preparing for the possibility of either scenario with two strategies: considering deploying another dose of their existing vaccines to boost immune system fighters and developing variant-specific boosters.

In its statement last week, Pfizer seemed to indicate both those scenarios could be at play, suggesting that its vaccine’s potency generally waned after six months or so, but also that the global rise of the Delta variant could be contributing to some loss of potency. While Pfizer said it was working on a Delta-specific booster, the company said it and its partner BioNTech believe that a third dose of its existing vaccine “has the potential to preserve the highest levels of protective efficacy against all currently known variants including Delta.”

Other studies, however, have indicated that full regimens of the vaccines (in the U.S., two doses of either the Pfizer or Moderna immunization, or the one-shot Johnson & Johnson vaccine) retain their protective power against Delta, particularly when it comes to preventing the worst outcomes of a Covid-19 infection. In fact, Delta seems to have less ability to get around the body’s immune response than another variant, Beta (also known as B.1.351), though that variant is not as prevalent as Delta. Pfizer, in its statement about the possibility of boosters, also acknowledged this.

The hubbub about boosters gets at a bigger debate about what we expect from vaccines. Pfizer’s statement noted that while its vaccine may have lost a step in terms of preventing infection entirely or any symptomatic illness, it was still maintaining its ability to protect people from serious illness. So if waning immunity or the rise of variants leads to more infections — but they’re almost universally mild or moderate cases and aren’t driving waves of hospitalizations or deaths — does that justify giving people a booster to protect them from any infection? The question becomes more fraught when considering the global inequity in vaccine access.

If there are boosters, what does that mean for the businesses of Pfizer and other drug makers?

The U.S.’s big three makers of Covid-19 vaccines — Pfizer, Moderna, and Johnson & Johnson — have already made tens of billions of dollars during the pandemic, and the continued global demand for doses suggests they’ll make billions more. But the sustained profitability of those vaccines depends on wealthy nations deciding they need to buy third, fourth, and umpteenth doses to sustain immunity among their populations. Pfizer is leading the way in filing for authorization of a third dose, but J&J and Moderna, which is also developing a variant-specific booster, are likely to follow.

The debatable need for boosters is of particular importance to the makers of second-generation Covid-19 vaccines. Novavax, whose vaccine is yet to secure emergency authorization, is counting on a market for booster shots to make a return on its investment. Sanofi, whose GlaxoSmithKline-partnered vaccine ran into a delay last year, is in a similar position.

SVB Leerink analyst Geoffrey Porges expects Pfizer and Moderna to dominate the U.S. market for Covid-19 vaccines into 2023. But if boosters become a necessity, as Porges assumes they will, the market will become more fragmented, with space for a multitude of competitors to build sustainable businesses off of endemic Covid-19.

Should the U.S. and other wealthy countries really roll out booster shots when many people around the world haven’t yet had their first jab?

Vaccine inequity is a deeply troubling problem in this pandemic. Tedros, the WHO’s director-general, has repeatedly appealed to wealthy countries to find a solution — and castigated them for not moving quicker. If affluent countries begin to dole out third doses to large segments of their populations, the problem he has railed against will only worsen.

The Bloomberg vaccine tracker notes that of the 3.41 billion doses of vaccine that have been administered so far, 22% have been given in 27 countries that have only 10.4% of the global population. In a number of African countries, less than 1% of the populace has been vaccinated. And in a number of countries, health workers remain unvaccinated, Tedros said.

“We’re making conscious choices right now not to protect those most in need,” he said.

Helen Branswell, Matthew Herper, Lev Facher, Damian Garde, and Andrew Joseph contributed reporting.

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Tracy Carr
Tracy is a veteran journalist and medicine graduate. she mostly writes about the health industry and biotech.
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