Big gap between Pfizer, Moderna vaccines seen for preventing COVID hospitalizations

A dose of Pfizer-BioNTech COVID-19 vaccine is being prepared at a mobile vaccine clinic in Los Angeles. (Irfan Khan / Los Angeles Times)
Amid lingering concerns that the protection offered by COVID-19 vaccines may deteriorate, a report released Friday by the Centers for Disease Control and Prevention found America's workhorse syringe is significantly less effective than many in long-term prevention of serious illnesses Experts had noticed.
Data collected between March and August from 18 states suggests the Pfizer BioNTech vaccine reduced the risk of hospitalization with COVID-19 by 91% in the first four months after receiving the second dose. However, after 120 days, the effectiveness of the vaccine drops to 77%.
Meanwhile, Moderna's vaccine was 93% effective in reducing the short-term risk of COVID-19 hospitalization and remained 92% effective after 120 days.
Overall, 54% of fully vaccinated Americans were vaccinated with Pfizer vaccination.
The surprising results came when an advisory panel to the Food and Drug Administration recommended that all Americans 16 and older be offered booster doses of the Pfizer vaccine. 16 out of 18 experts told the agency in a striking rebuke that they had not collected enough data to make a third shot the norm.
In lengthy briefings to the panel, Pfizer officials referred to the results of clinical trials involving 306 mostly healthy participants to argue that a booster dose "restores" the 95% vaccine effectiveness rate previously seen in the pandemic.
Company officials also touted evidence from Israel that Booster launched after the increase in hospital admissions for fully vaccinated people. Those hospital stays dropped dramatically after the third dose was given, Israeli scientists said.
However, the panel members made it clear that despite Pfizer's aggressive stance, insufficient evidence has been gathered that a third shot is safe for young people and for those at lower risk of developing COVID-19 seriously.
"We need age-specific data" about the safety and protective benefits of another booster, said Dr. Ofer Levy, a panel member who directs the Precision Vaccines program at Boston Children's Hospital.
FDA approval for booster syringes for anyone ages 16 and older would be seen as something "close to a mandate," said Dr. Eric Rubin, a panel member and infectious disease expert at Harvard T.H. Chan School of Public Health. Rubin feared that such a move could redefine what it takes to be considered fully vaccinated against COVID-19.
"Neither of us is here," he said.
But others apparently. Dr. Anthony Fauci, President Biden's top vaccine advisor, has strongly advocated booster syringes and said ahead of Friday's vote that it would be a mistake not to endorse vaccinations.
And in mid-August, Biden himself said that from the week of September 20, his government would begin providing booster syringes to those who had been vaccinated for at least eight months.
Biden then warned that his plan was subject to FDA approval. But his announcement raised concerns about political interference in an issue that required the unhindered evaluation of scholars.
"This should show the public that the members of this committee are independent of the FDA," said Dr. Archana Chatterjee, Dean of Chicago Medical School, after the vote. "In fact, when asked to serve on this committee, we bring our voices to the table."
The panel unanimously agreed that a third vaccination of the vaccine, now sold under the Comirnaty brand, should be offered to selected groups: those aged 65 and over, those at risk of serious illness and those, including health workers, whose occupation puts them too high Risk of contagion.
Dr. Peter Marks, who leads the FDA's drug and vaccine evaluation, told panel members that the agency could bless booster vaccinations with an emergency clearance - a regulatory move that falls short of Pfizer’s full approval.
The company did not comment on the panel's vote on Friday.
Researchers in the United States have been warning for months that the immunity conferred by COVID-19 vaccines could weaken. The CDC reported that as of late July, nearly three-quarters of the 469 people recorded in an outbreak in Massachusetts were fully vaccinated. And the agency has launched several studies aimed at uncovering changes in vaccine effectiveness among health care workers and others who were vaccinated early.
But virtually all of these infections appeared to be mild. And health officials eager to get vaccine skeptics to step up their vaccination - including Fauci and Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention - have repeatedly praised the vaccines for keeping most fully vaccinated people out of hospitals.
The new report on the declining effectiveness of vaccines challenges this expectation.
Pfizer-BioNTech COVID-19 vials are on a tray at a mass vaccination clinic in Ontario, California (Irfan Khan / Los Angeles Times)
Researchers from across the country found striking differences between two mRNA vaccines that were long thought to be interchangeable.
When the Moderna vaccine received emergency approval in December, the company reported that 30 people in its clinical trial developed severe cases of COVID-19, including nine who had to be hospitalized. All 30 patients were in the placebo group, which resulted in the vaccine being 100% effective against serious illness.
Ten people in Pfizer's first clinical study developed severe cases of COVID-19. Nine of them were in the placebo group, including seven who were hospitalized, resulting in a vaccine effectiveness of 88.9% against serious illness.
After Moderna and Pfizer's vaccines were released to the public, their records of preventing COVID-19 hospitalizations were head-to-head for the first four months - 93% and 91%, respectively. But the degree of protection differed afterwards.
When they specifically focused on the 120 day period after the second dose, the study authors found that the Moderna vaccine remained 92% effective in preventing COVID-19 hospitalizations. But the equivalent value for the Pfizer vaccine was 77%.
The results were published in the CDC's Morbidity and Mortality Weekly Report.
Both the Pfizer and Moderna vaccines are based on mRNA technology, which gives temporary instructions to the body's muscle cells that help it recognize the spike protein, a key element in the structure of the coronavirus. But "actually they are not necessarily interchangeable," said Dr. Timothy Brewer, Professor of Medicine and Epidemiology at UCLA.
Each vaccine is formulated and administered differently, Brewer said, and those differences could affect the strength and duration of protection of the two vaccines.
Moderna's shot contains 100 micrograms of vaccine, more than three times the 30 micrograms in the Pfizer shot. And Pfizer's two doses are given three weeks apart, while Moderna's two-shot therapy is given four weeks apart.
Brewer also pointed to evidence that the Moderna vaccine appeared to produce higher levels of a major antibody than the Pfizer vaccine.
“We know from other studies that neutralizing antibody levels drop over time. So if you start at a higher level you have to go further before you go down to the point where the effectiveness starts to wear off, ”he said.
Dr. Robert Murphy, who heads Northwestern University's Institute for Global Health, said the Pfizer vaccine's reduced protection against serious diseases could bolster the booster case for anyone who received the vaccine, not just those identified by the FDA advisory panel specific groups.
"Based on the data I've seen, people who received the Pfizer vaccine would benefit from a booster dose at this point," he said. "I don't understand why we have to wait until the younger ones get sick and are hospitalized."
But dr. Arnold Monto, chairman of the FDA advisory panel, welcomed the agency's willingness to withhold a full call for boosters until a stronger case can be made. And he suggested boosters for everyone could still get the nod as more evidence piles up.
“That's the beauty of the emergency approval,” said Monto, an epidemiologist at the University of Michigan. "It can be changed based on changing dates."
This story originally appeared in the Los Angeles Times.

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