A new study by the U.S. Centers for Disease Control and Prevention has found that even though protection from the Moderna and Pfizer COVID-19 booster shots weakens after approximately four months, the boosters still provide significant protection from SARS-CoV-2 after that.
In the recent study, published on February 11, researchers analyzed 241,204 COVID-related emergency department (ED) and urgent-care center (UC) encounters, as well as 93,408 hospitalizations across 10 U.S. states. These cases occurred between August 2021 and January 2022, a period in which omicron was the most contagious COVID-19 strain. In terms of protection against hospitalization, the study found that two months after the third shot, vaccine effectiveness stood at 91%. After four months, it dropped to 78%. When it came to protection against ED or UC visits, vaccine effectiveness slipped from 87% to 66% over that same period. It is still better than no protection at all, but there is a clear decrease.
While there have been numerous studies into the effectiveness of the two primary COVID-19 shots, research into the levels of protection offered by a third shot has been limited. However, the rise of the highly infectious omicron variant has triggered the need for further research. According to the scientific journal Nature, several months after Israel became the first nation to make a third shot available to the public, a study found that older Israelis who received their third shot were far less likely to test positive for COVID-19 or to develop life-threatening symptoms and related illnesses than those who only had their two primary shots.
Like all studies, this one had a few limitations. The main one being that researchers only focused on people who sought medical treatment for COVID-19, meaning that COVID-19 infections that did not require medical treatment were not factored into the data. This aspect means the research could be skewed more toward immunocompromised people or older people.
So, since we know that the third shot can give us further protection against COVID-19 but that it weakens over time, this raises the question: Will we need a fourth shot? “The finding that protection conferred by mRNA vaccines waned in the months after receipt of a third vaccine dose reinforces the importance of further consideration of additional doses to sustain or improve protection against COVID-19,” researchers said in the study. In some countries a fourth shot has already been rolled out to select groups of people. The CDC has already endorsed the idea of fourth shots for immunocompromised people in the U.S., as SELF previously reported. In France health authorities authorized a fourth COVID-19 shot for organ transplant recipients who had not responded to three earlier doses. In Sweden a fourth shot was recently recommended to people over the age of 80 and to those residing in nursing homes. In the U.K. a fourth shot is being offered to people aged 12 and older with severely weakened immune systems.
For now it’s clear that even when vaccine and booster protection wanes, inoculation against COVID-19 remains the best bet for staying safe. “All eligible persons should remain up to date with recommended COVID-19 vaccinations to best protect against COVID-19–associated hospitalizations and ED/UC visits,” researchers said in the study.
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