- A team of researchers from Israel and the United States recently analyzed the effectiveness of a third dose of Pfizer’s COVID-19 vaccine for preventing severe COVID-19 outcomes.
- They found that an additional “booster” shot can reduce the risk of serious complications, compared to just two doses of vaccine.
- However, global inequalities and hesitation about vaccines are ongoing challenges to vaccination efforts.
SARS-CoV-2 infections have increased again in many parts of the world in 2021, mainly driven by the
Health care officials are concerned that the effectiveness of the current vaccination is declining, not against this new strain. In response, many governments want
The Israeli government has deployed the third dose of the Pfizer vaccine before and during the country’s fourth wave of pandemic in the summer of 2021.
A team led by scientists from Harvard University and Israel’s Clalit Research Institute recently concluded that this additional inoculation could significantly reduce the risk of serious complications from COVID-19.
Their paper, which appears in
The team analyzed data from Clalit Health Services, Israel’s largest healthcare organization.
The scientists tracked 728,321 individuals who received a third Pfizer COVID-19 vaccine between July 2020 and September 2021. These participants were matched with an equal number of people who received only two doses of the vaccine.
The authors explain: “In this study, we estimated effectiveness from day 7 after the third dose, which is comparable to the period used to define full vaccination after the second dose. Our choice is supported by high levels of antibodies in individuals 7 days after administration of the third dose.”
Primary outcomes were hospitalization related to COVID-19, major illness, and mortality, according to National Institutes of Health (NIH) criteria.
As part of their analysis, the researchers adjusted for possible confounding factors, including sociodemographic factors, pre-existing health problems and behavioral factors.
The data showed that people who received the COVID-19 booster injection had a 93% lower risk of hospitalization, compared to people who received their second injection at least 5 months earlier.
Similarly, people on a third dose had a 92% lower risk of serious illness and an 81% lower risk of death from COVID-19.
According to the team, the estimated effectiveness of the third dose against hospitalizations and serious complications was “comparable between men and women, and between those aged 40-69 and those aged at least 70.”
- 65 years or older
- 18 years or older and an underlying medical condition
- 18 years or older and living or working in a high-risk environment
- 18 years or older and received a Johnson & Johnson COVID-19 vaccine
The CDC also says people can choose which COVID-19 booster vaccine they want to receive.
In a survey by the Kaiser Family Foundation, 43% of fully vaccinated adults said they will “definitely” receive a COVID-19 booster vaccine when it becomes available. Another 24% said they “probably will” if it’s recommended for people like them. By the time the survey was completed in October 2021, 10% of respondents had already received a booster.
Suitable but not informed
Donald J. Alcendor, Ph.D., is an assistant professor of cancer biology at Meharry Medical College. He is also an associate professor of pathology, microbiology, and immunology at Vanderbilt University School of Medicine.
In an interview with Medical news todaynoted Dr. Alcendor notes that many people in the US qualify for boosters but don’t realize this.
He explained that the CDC’s eligibility guidelines apply to people who are at least 18 years old and have an underlying medical condition, such as:
- diabetes mellitus
- heart condition
- chronic lung diseases
- overweight or obese
- a substance use disorder
dr. Katherine O’Brien is a professor at the Bloomberg School of Public Health and the Executive Director of the International Vaccine Access Center, at Johns Hopkins University.
“The first is […] if you belong to a category of people who did not respond adequately to the first two doses you received. We have some information that some immunocompromised people may need to get a third dose because those first two don’t do what they do in normally healthy people.”
dr. O’Brien also said vaccine protection may deteriorate over time. However, she noted, “We don’t see strong evidence that it is necessary to provide a third dose to people who have already been vaccinated.”
dr. Alcendor is concerned that millions of people in the US have not been vaccinated against COVID-19. He has also observed that doubts are growing among individuals who are hesitant to receive vaccines and among parents who protest against vaccine mandates for children.
“This will result in unvaccinated populations in the US allowing this virus to continue to evolve and cause breakthrough infections in the general population to expand this pandemic.”
He further warns that “global inequalities in vaccine distribution represent a quiet storm that must be dealt with in the same way as for polio and smallpox.”
In the WHO podcast, Dr. O’Brien on this point in:
“We are currently in a very unequal situation as to who has already received the first and second dose to protect against the serious consequences. In low-income countries and low [to] middle-income countries, they only received about 1%, 2%, 5% of the population [the] vaccine already.”
“So the focus for delivery should now be on protecting those people who are not yet protected by vaccines at all. It will reduce transmission, it will reduce the likelihood of more variants developing, and it will give us time to see more evidence about whether or not booster doses are needed.”
– dr. Katherine O’Brien
The authors of this study cite several limitations. First, they were unable to generate reliable estimates of secondary outcomes; namely infection and symptomatic infection.
Also, as an observational study, this analysis could not explain all factors that may have influenced the outcomes.
In addition, the authors state, “Due to the relative scarcity of events in individuals younger than 40 years of age, we were unable to evaluate the vaccine’s effectiveness in this age group.”
The scientists also acknowledge that “this vaccine effectiveness study did not investigate potential adverse clinical events and health care overuse associated with the administration of a third dose.”
The study excluded people who probably got their booster dose early; this included health professionals and residents of long-term care facilities.
Meanwhile, several authors were affiliated with or compensated by Pfizer. MNT asked Dr. Alcendor, who was not involved in the investigation, whether these ties to the company may have influenced the results of the investigation.
He replied, “Vaccine manufacturers are always trying to minimize harm to their bottom line, but that’s why we have a data safety oversight board, the FDA Advisory Committee. […] and the CDC Advisory Committee, who are impartial and watch over us. There is always a chance of misuse of data, but the oversight of vaccines is quite strict.”
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