What to Know About a Fourth COVID-19 Vaccine Dose

Most people ages 12 and older are considered “up to date” with their COVID-19 vaccines if they received either three doses of the mRNA shots from Pfizer-BioNTech or Moderna, or two doses of Johnson & Johnson’s Janssen vaccine. However, some experts believe that a second dose will be necessary in the future.

Washington Post ReportsPfizer and BioNTech today announced plans to apply for authorization by the U.S. Food and Drug Administration, (FDA), for a fourth dose their vaccine. The request will be made for people aged 65 and above. In the past few days, Albert Bourla, Pfizer’s CEO, has said that he believes everyone will one day need a fourth dose in order to help prevent infections (a move that would have obvious benefits for the company’s bottom line.)
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In order to authorize a fourth shot, the FDA will consider troubling signs that the immunity provided by the vaccines is starting to wane, which could make people more vulnerable to COVID-19’s more severe effects. Recent DataThe U.S. Centers for Disease Control and Prevention published data showing that COVID-19 protection declined even after a booster of the Pfizer BioNTech and Moderna vaccines. From Aug. 2021 to Jan. 2022—a time span that includes waves of both Delta and Omicron variants—the booster was 91% effective at protecting against hospitalization in the first two months after people received it, but dropped to 78% four months after the shot. The booster’s efficacy in preventing COVID-19 symptoms-related hospitalizations was also declining. From 87% two months prior to the shot, to 66% three to five months later.

“We don’t know when you get to six months, seven months, or eight months after the third dose whether that 78% is going to go down to 60%, 50%, or 40%,” says Dr. Anthony Fauci, the White House’s chief medical advisor on COVID-19 and director of the National Institute of Allergy and Infectious Diseases. “For that reason, you are going to hear serious consideration for giving a fourth boost to the elderly and those with certain underlying health conditions. What we might be seeing in the reasonable future is that individuals, merely on the basis of age, and perhaps some underlying health conditions yet to be determined, would get an immediate boost.”

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The CDC has already We recommendA fourth dose of mRNA vaccine is available for patients with weak immune systems. This includes transplant patients as well as those who are undergoing chemotherapy. Other countries follow similar guidelines. Israeli officials went one further. On Jan. 22, after hospitalizations and cases increased, they authorized the fourth dose of Pfizer BioNTech’s mRNA vaccine. This was for healthcare workers and those over 60. The decision was based on early data from Israel’s Ministry of Health and researchers at several Israeli universities showing that among nearly a million vaccinated people over age 60, a fourth dose of the vaccine offered up to twice the protection against getting infected, and up to three times the protection against severe illness, compared to those who received three doses.

Evidence is mounting that vaccine-induced immunity continues to decline. Although antibodies that are produced immediately following vaccinations can be quite short-lived, scientists have known for years that vaccines trigger the body to produce additional immune defenses. T cells tend to last longer. These responses do begin to fade after a few months however says Dr. Otto Yang of the University of California Los Angeles. He says that existing vaccines might need additional booster doses to maintain sufficient antibody and T cells numbers to prevent severe diseases.

However, whether every person needs another vaccine and whether they can expect to get one every other year or just once every two years depends on how the vaccines are used. The vaccines are not intended to stop people getting the virus. They were designed to help them avoid getting very sick from COVID-19 and keep them out of intensive and hospital care. Remembering that goal, says Dr. Paul Offit, director of the Vaccine Education Center and professor of pediatrics at Children’s Hospital of Philadelphia, is useful when thinking about whether a fourth dose is necessary for most people.

“We got hung up using the word ‘breakthrough’ in describing mild illness,” he says, referring to the term for any infection occurring among vaccinated and boosted people (most of which were mild or even asymptomatic). “But that’s a win—it meant the vaccine was working for you and protected you from serious illness. We have developed a zero tolerance strategy that we are going to have to get over: the idea that it’s not okay to have mild illness after you’ve been vaccinated.”

Offit claims that the COVID-19 vaccine should be used to protect against severe illness. However, the data is not sufficient to support the use of boosters for healthy adults. “I think we have to accept the notion that this is a three-dose vaccine in certain groups and a two-dose vaccine in others,” Offit says.

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Offit, who serves on the FDA vaccine advisory committee of independent experts that reviews data and makes recommendations to the FDA about whether or not a vaccine is safe and effective, says that trying to protect the world’s population from mild disease with continued booster doses isn’t a realistic or practical public health goal. Now the question is how do you balance the potential side effects of vaccines and any possible marginal benefits in protecting from mild illnesses. For the mRNA vaccines, this includes the possibility of inflammation of the heart tissue. “Everything has costs, including boosting,” he says. “If it doesn’t benefit you in terms of protection against serious illness, then you have to consider the side effects.”

Fauci states that officials from the health department will closely monitor hospitalization rates among those who were vaccinated in the next weeks and months. A rise would indicate a concern about the level of immunity even for severe diseases, and could call for another booster. “We don’t know now if we are going to need it, but as long as this virus hangs around, I would not be surprised if we are going to need one more shot than we have had,” he says.

He and others also don’t anticipate continuing to boost as new variants crop up. That strategy was developed out of an urgency to eradicate the virus from as many people possible. But it’s not a durable or practical game plan over the long term. “We’ve been chasing our tails with every variant, and we will perpetually be behind [the virus],” says Dr. Kirsten Lyke, professor of medicine at University of Maryland, who spearheaded studies about mixing and matching different types of COVID-19 vaccines.

The National Institutes of Health has launched new research to find a better way of providing booster shots. Rather than responding to new variants as they emerge and hoping the existing vaccines continue to protect against severe disease, scientists there are mapping out SARS-CoV-2’s mutations and trying to design vaccines against broad collections of changes that would ideally quell a number of different, but related strains that the virus may generate in the future. This study involves up to 1,500 participants at 25 different sites. “By mid-summer, we would like to put all the data together so we can make a more scientific assessment as to whether additional boosters will work, whether we will need them, and which one we might need to use,” says Lyke.

The future rates of hospitalizations among the vaccinated or boosted population will determine whether a fourth dose is recommended. If they increase, health officials may recommend another dose. In the meantime, Fauci says scientists at the National Institute of Allergy and Infectious Diseases’ Vaccine Research Center are investigating whether that additional dose should come from the same vaccine people have been receiving, or whether that additional dose should be with a new vaccine that targets a specific variant, such as Omicron. The original booster has produced similar immune reactions to the variant-specific boosters used in non-human primates. “Given the fact we have waning immunity, we may need a regular boost at intervals yet to be determined,” Fauci says.


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