- Researchers analyzed over 11,000 hospital admissions and emergency department visits to see how effective COVID-19 vaccines prevent illness.
- They found that the three doses of the Pfizer mRNA COVID-19 vaccine are very effective at preventing hospitalizations initially.
- While that high level of efficacy wanes, experts say the vaccines still provide key protection against COVID-19.
“Pfizer BioNTech COVID-19 booster doses significantly improve protection against Omicron, although that protection seems to wane after 3 months against emergency room visits, and even for hospitalization,” lead author, Sara Y. Tartof, PhD, a research scientist and infectious disease epidemiologist at the Department of Research & Evaluation for Kaiser Permanente Southern California said in a statement.
Researchers analyzed over 11,000 hospital admissions and emergency department visits that didn’t result in hospital admission for acute respiratory infection.
They focused on Kaiser Permanente patient records in Southern California from December 1, 2021, through February 6, 2022, when Delta and Omicron variants were circulating. That time period was also the peak of the Omicron wave in California.
According to researchers, after two-doses of the vaccine, the vaccine effectiveness against Omicron was 41 percent against hospital admission and 31 percent against emergency department visits at nine months.
They found that a Pfizer vaccine booster shot provided roughly 80 to 90 percent protection against severe outcomes caused by Delta and Omicron immediately after it was given.
But the effectiveness against Omicron-related hospitalization started to wane at about the three-month mark.
The vaccine was 85 percent at preventing hospitalization within three months of being administered. But the effectiveness dropped to 55 percent after the three-month mark.
They also looked at how effective the vaccine was at preventing Omicron-related emergency department visits that did not result in hospitalization. They found three doses of the Pfizer vaccine were 77 percent effective within three months of being administered. It declined to 53 percent after the three-month mark.
“Although the Pfizer COVID-19 protection levels against omicron after 3 doses are substantially higher than those seen after 2 doses, they are less than those observed for delta or other COVID-19 strains,” Tartof said in a statement.
She cautioned that additional doses of “current, adapted, or novel COVID-19 vaccines” might be required to maintain high levels of protection against new waves of infection caused by Omicron or future variants with similar potential to escape protection.
Experts stress that COVID-19 vaccines are a vital part of ending the pandemic, and even if their effectiveness wanes, they provide key and important protection against severe disease.
“One of the misunderstandings that people have about the COVID vaccine, and there’s lots of reasons why they are confused – they think that if you’re vaccinated, you won’t get the virus,” said Peter Pitts, Former FDA Associate Commissioner and president of the Center for Medicine in the Public Interest.
While that’s true for many people, he explained, the vaccine doesn’t provide complete protection from infection.
“Especially when we have a mutation that’s highly infectious,’ Pitts said. “It [vaccination] mitigates the symptoms.”
He added that with currently available vaccines, the mitigation of serious symptoms and hospitalizations is “extremely robust, as witnessed by high infection, low hospitalization.”
“The reality is that the vaccines as they currently exist are extremely effective at accomplishing their mission of keeping people out of the hospital and dying,” confirmed Pitts.
Pitts said it is expected that vaccine efficacy will drop over time. This may partly be due to waning antibodies, but this study did not measure antibody levels.
Pitts explained that this research proved a hypothesis that vaccine protection wanes over time, and the vaccine provides greater protection against some variants than others.
“But it’s still effective,” he said. “It isn’t necessarily less effective.”
He compared it to needing 20 dollars to buy an item when you already have 40 dollars.
“And then the price goes up to 25 dollars; you still have enough money to pay for it,” said Pitts. “So the big question is; what is robust enough?”
“This study does not answer that question,” he continued. “Because we don’t necessarily know how to properly create those studies.”
Robert G. Lahita, MD, PhD, Director of the Institute for Autoimmune and Rheumatic Disease at Saint Joseph Health and author of Immunity St explained that vaccines wane over time. He suspects that COVID vaccination may be needed annually, like the flu vaccine.
“This is not an unexpected problem when you consider the nature of the virus,” Lahitatold Healthline.
He pointed out that, although different from COVID-19, some common human coronaviruses are related to the common cold, which people can contract frequently. So he doesn’t find it surprising that vaccine-induced immunity might be short-lived. But he pointed out that the vaccines have been effective enough that hospitalizations are down nationwide.
“I would say that research in the future will show that the vaccine lasts differently for different people,” “This would depend on age, lifestyle, overall health, etc.
He also noted that the vaccine efficacy of 53 percent at three months or longer is similar to the protection a flu shot might provide.
New research finds the efficacy of Pfizer’s COVID vaccine was initially powerful but waned significantly after three months during the height of the Omicron wave.
Experts say it isn’t unusual for vaccine effectiveness to wane over time and that the vaccines are significantly protective at preventing severe disease for many people.