Is a fourth dose of the covid-19 vaccine necessary?
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(CNN) --
As the world approaches the second anniversary of the World Health Organization's declaration of the Covid-19 pandemic on March 11, more countries are launching or discussing the possibility of fourth doses. of the coronavirus vaccine for the most vulnerable.
In the United States, top public health officials say they are monitoring "very carefully" whether or when a fourth dose is needed.
Israel was the first nation to implement fourth doses, announcing in December that adults over 60, medical workers and people with weakened immune systems were eligible to receive the additional injection if at least four months had passed since their third dose.
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More recently, the Swedish Public Health Agency announced last week that second booster doses are recommended for all people over the age of 80 in the country.
In the United States, health officials stressed late last year that fourth doses were not yet needed and said it was too early to discuss a possible fourth dose of the coronavirus vaccine for most people.
Now, the US Food and Drug Administration (FDA) "is continually analyzing emerging data on the pandemic and its variants in the United States and abroad to assess the potential usefulness and composition of booster doses," FDA spokeswoman Alison Hunt wrote in an email.
to CNN on Friday.
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why autumn
She confirmed that although Dr. Peter Marks, director of the FDA's Center for Biological Evaluation and Research, has noted that there is still a lot of uncertainty about how the pandemic may evolve, he has also said that it is possible that a fourth dose could be administered to as we move into the fall.
The fall window coincides with the administration of flu shots, which could be convenient for people and makes scientific sense because respiratory viruses, such as coronavirus and influenza, tend to peak in the winter months that follow.
"As more data becomes available on the safety and efficacy of COVID-19 vaccines, including the use of a booster dose, we will continue to evaluate the rapidly changing science and keep the public informed," Hunt wrote.
"Any determination that additional booster doses are needed will be based on data available to the agency."
On whether or when the FDA authorizes a fourth dose for the public, the next step would be for the US Centers for Disease Control and Prevention to review the data before making a recommendation for use, as the FDA has done. agency for other coronavirus vaccine recommendations.
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“Vaccination and reinforcement will be critical”
The United States has seen significant improvements recently in Covid-19 cases, hospitalizations and deaths.
Through Friday, cases were down 44% from the previous week, hospitalizations were down 26% and deaths were down 13%, according to data from Johns Hopkins University.
"Vaccination and boosting will be critical to maintaining that downward trajectory, particularly when you're talking about the red curve of severe disease leading to hospitalization," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, during a White House Covid-19 Task Force briefing on Wednesday.
The "potential future requirement" for an additional booster or a fourth injection of the Pfizer/BioNTech or Moderna mRNA vaccines or a third dose of the Johnson & Johnson vaccine is "very carefully monitored in real time," Fauci said.
"And the recommendations, if necessary, will be updated based on the data as it evolves."
The CDC does not recommend fourth doses of the coronavirus vaccine for the general public, but the agency updated its guidelines in October to note that certain people with moderate or severe immunosuppression may receive a fourth dose of Moderna or Pfizer/BioNTech vaccines.
"For immunocompetent people, a single booster injection continues to provide high levels of protection against serious illness caused by omicron," Fauci said Wednesday.
"This should not be confused with the fact that for many immunocompromised people, a second booster injection, that is, a fourth dose of an mRNA, is already recommended because of what we know about their poor response to the initial regimen."
Meanwhile, vaccine manufacturers continue to study fourth doses in larger populations.
Fauci: Current vaccination regimen gives strong protection 0:59
“We recognize the need to be prepared”
Pfizer announced in January that it has studied the safety and efficacy of a fourth dose as part of its ongoing investigation of an omicron-specific coronavirus vaccine among healthy adults ages 18 to 55.
For that study, the participants have been separated into three cohorts.
One includes 600 people who received three doses of the current Pfizer/BioNTech coronavirus vaccine before enrolling in the study.
As part of the research, they will receive either a fourth dose of the current vaccine or one dose of the omicron-emphasis vaccine.
"While current research and real-world data show that boosters continue to provide a high level of protection against serious illness and hospitalizations due to omicron, we recognize the need to be prepared should this protection decline over time and potentially help to combat omicron and new variants in the future," Kathrin Jansen, senior vice president and chief vaccine research and development officer at Pfizer, said in the company's announcement of the study.
A study published by the CDC last week showed that protection against COVID-19 hospitalization and visits to the emergency department or urgent care is much greater after a third dose of vaccine than a second dose, but that protection decreases over time.
With the dominant omicron variant in the United States, the effectiveness of the vaccine was 87% against visits to the emergency department or urgent care for COVID-19 and 91% against hospitalizations within two months after a third dose.
Effectiveness fell to 66% and 78%, respectively, by the fourth month, the data showed.
“However, the 78 level is still a good area of protection,” Fauci said Wednesday.
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Will omicron disappear?
Dr. Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington, told CNN on Friday that he thinks having a fourth dose "makes very little sense" at this point, but possibly makes more sense. this coming fall or winter.
"And because omicron is going to wear off," he said, "the immunity to the third dose goes down, so the fourth dose will probably go down as well. So maybe we want to schedule a fourth dose booster for when there's a new variant or for next winter. So I think right now, unless you're immunocompromised or older, unless you have some personal risk, it doesn't make a lot of sense."
Research showing some decline in immunity after a third dose has led to further debate about whether or when a fourth dose might be necessary.
"As with everything else, health departments are looking at this data coming out and waiting for guidance from the CDC and from drug manufacturers. Drug manufacturers have been keeping an eye on the effectiveness of vaccines," he told CNN. on Friday Lori Tremmel Freeman, executive director of the National Association of County and City Health Officials.
The timing of the fourth dose not only depends on waning immunity "but also depends on whether we see more variants emerging and what we find out in terms of additional vaccine effectiveness for any new emerging infections," Freeman said.
If fourth doses are needed, "health departments would go into preparation mode to administer the fourth dose the way they have for previous doses," Freeman said.
What worries local public health officials most, however, is the slow — and declining — rate of people completing their third dose, she noted.
About 65% of the US population is fully vaccinated with at least their initial series, and about 28% of the population has received a booster dose, according to the CDC, as of Friday.
But the rate of booster doses being given has slowed to one of the slowest rates yet.
"As time goes on, if there is a need for a fourth dose, we are already behind in people getting the third dose," Freeman said.
"Then all of a sudden we could have a pretty large segment of the population that is not up to date on vaccines because they are two doses behind, potentially, and more people could get sick."
CNN's Katherine Dillinger contributed to this report.