The advice of the FDA’s advisory panel on the matter will not be binding, but the agency is likely to consider it. If the FDA authorizes a booster dose, the decision on whether to give them broadly will be taken up by a separate advisory committee convened by the Centers for Disease Control and Prevention. There has been no date set yet for a meeting of that group, the Advisory Committee on Immunization Practices.
Still, any decision by the FDA that limits the approval for booster shots, or even expresses hesitancy about how they should be used, will be seen as a rebuke to the Biden administration, which in August took the unusual step of unveiling a plan to offer boosters to the U.S. population, ahead of decisions from the FDA and the CDC.
Among those who have challenged the need for boosters at this point are two senior FDA officials who recently announced they will retire from the agency this fall, a move seen to be motivated by their disagreement with the administration on the booster question. Marion Gruber and Phil Krause, director and deputy director, respectively, of FDA’s Office of Vaccines Research and Review, were also co-authors of a paper published Monday in The Lancet that argued against the need for booster shots for the general public at this time.
In the briefing documents made available Wednesday, Pfizer argued that the effectiveness of its vaccine is declining and that a third dose would return efficacy to the 95% level seen in clinical trials.
Recent data from Israel showed the efficacy of the vaccine against infection with SARS-CoV-2 dropped from 95% in January to 39% in June. In an analysis of Pfizer’s own Phase 3 trial, which resulted in the vaccine’s approval, the incidence of breakthrough cases was higher among patients who received their second dose before December 2020 than in those who received their second dose after March.
The company also released new data from a study conducted by Kaiser Permanente in Southern California that showed the waning efficacy is likely due to the vaccine becoming less effective over time, not because the new Delta variant is more resistant to the vaccine.
In the Kaiser data, the efficacy of the vaccine at preventing SARS-CoV-2 infection with the Delta variant dropped from 93% for those vaccinated less than one month to 53% for those vaccinated more than four months ago. For other variants, this drop was from 97% to 67%. At this point, about 88% of SARS-2 viruses detected globally are from the Delta family.
However, the vaccine still did a very good job preventing hospitalizations in this dataset, reducing hospitalization by 93% in cases infected with the Delta variant.
“It should be recognized that while observational studies can enable understanding of real-world effectiveness, there are known and unknown biases that can affect their reliability,” FDA scientists state in their report. “Due to these biases some studies may be more reliable than others. Furthermore, US-based studies of post- authorization effectiveness of [the vaccine] may most accurately represent vaccine effectiveness in the US population.”
The FDA documents assessed questions about the safety of giving a third dose of the vaccine, noting that for some issues, there are no answers. For instance, it is not known if a third dose would trigger elevated rates of myocarditis and pericarditis, a side effect seen mainly in males under the age of 40.
“It is currently not known if there will be an increased risk of myocarditis/pericarditis or other adverse reactions after a booster dose of Comirnaty. These risks and associated uncertainties have to be considered when assessing benefit and risk,” the agency’s scientists wrote. Comirnaty is the brand name of Pfizer’s vaccine.
Meanwhile, an analysis of vaccine efficacy from the United Kingdom — the first country to begin vaccination with the vaccines developed in the West — gives further ammunition to those who have argued that booster shots for all are not warranted at this time.
The analysis from Public Health England, which has not yet been peer-reviewed, found protection against hospitalization and deaths remains high for the Pfizer jab, even among older adults who are healthy.
“Given the sustained high [vaccine efficacy] against hospitalization and death, the additional benefit of a third dose against these more serious outcomes is limited in the current epidemiological situation,” the authors of the British study concluded. They added that vaccine efficacy “may, however, continue to wane over time and it is likely that booster doses may have a bigger impact on the more severe outcomes with longer intervals between the second and third doses.”
The most significant waning of protection is occurring in people aged 65 and older who have significant health issues, the paper said. It is based on a comparison of the vaccination status of nearly 1.5 million people who tested positive for Covid-19 to nearly 3.3 million people who tested negative for the virus.
“We found that waning was greatest among individuals in clinical risk groups, suggesting that this group should be prioritized for boosters, whenever they are recommended,” the authors said.
Despite the findings, Britain’s Joint Committee on Vaccination and Immunization recommended Wednesday that everyone who was at the front of the line when the country began its vaccine rollout last December should receive a booster shot, once six months had passed since their second jab.
Those listed as being at the head of the priority list for boosters in the U.K. are those living in long-term care facilities, adults 50 years of age and older, front-line health care workers and social workers, people 16 to 49 years old with underlying health conditions that put them at high risk of developing severe disease if they contract the virus, and adults who live with immunocompromised people.