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Researchers also found that COVID-19 vaccine effectiveness waned over time.
By: Naveen Athrappully
Flu shots provide moderate protection against COVID-19 infection and could reduce the risk of hospitalization and mortality from the illness, according to a recent study.
The Oct. 31 preprint study, published on MedRxiv, looked at data from 210,136 individuals to estimate the effectiveness of influenza vaccine (flu shot) against COVID-19 infection during the Delta and Omicron waves. The study found that taking an influenza vaccine provided “moderate protection” against COVID-19 infection.
Researchers claimed that earlier studies suggested a “large degree of protection” against COVID-19 from the flu shot. However, “our study was conducted in a larger patient population, and we were able to control for a larger set of confounding factors, including comorbidity,” it said.
Other studies have shown that COVID-19 vaccine protection against COVID-19 infection waned over time, a pattern that was “confirmed by our results,” the study stated.
Researchers said that flu shots had a “much lower estimate of effectiveness” compared to COVID-19 vaccination. However, “taking a flu shot is still advisable due to some extra protection and the risk of co-infection with influenza and SARS-CoV-2.”
Only individuals who had received COVID-19 vaccines manufactured by Pfizer or Moderna were included in the study.
“Some studies have found that individuals who have COVID-19 and the flu at the same time are at much greater risk of hospitalized disease and death compared with patients who have COVID-19 alone or with other viruses,” the study stated.
“Given the higher risk of hospitalized disease caused by co-infection, taking a flu shot should be encouraged to reduce the risk of COVID-related hospitalized outcomes and mortality.”
Among the 210,136 study participants, 31.9 percent were flu-vaccinated prior to the COVID-19 PCR test, out of which 14.2 percent had not received the COVID-19 vaccine. Out of the 68.1 percent of individuals who were not flu-vaccinated, 46.9 percent did not receive the COVID-19 shots.
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Researchers collected patient data from three sources—Corewell Health East, Corewell Health West, and Michigan Medicine healthcare system.
There were 18,468 (26.2 percent) flu-vaccinated subjects from Corewell Health East, 23,306 (22.7 percent) from Corewell Health West, and 25,272 (67.9 percent) from Michigan Medicine.
The study was funded by the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health. The authors declared that they had no competing interests while preparing the study.
“The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript,” the study clarified.
The findings of this study contradict an August 2022 study published in the Nature journal, which reported finding no significant positive impact of influenza vaccines on COVID-19.
The August study looked at 191,496 COVID-19 patients. An analysis of the health data “indicated no statistically significant differences between vaccinated and non-vaccinated groups in the term of mortality rate, hospital admissions, intensive care admissions.”
“There were no significant differences between those who had received the influenza vaccine and those who had not in COVID-19 clinical outcomes, except for mechanical ventilation which showed a significantly lower risk in the influenza vaccinated group compared to the non-vaccinated one,” it said.
Influenza Vaccine and COVID-19 Shots
The Oct. 31 MedRxiv study comes as the U.S. Centers for Disease Control (CDC) is recommending Americans to take the flu, RSV, and COVID-19 shots as part of the immunization plan for Fall and Winter 2023-2024.
“Immunization against these viruses remains the best protection for reducing the risk of serious illness, hospitalizations, long-term health impacts, and death,” the agency said.
Meanwhile, several studies show that there could be side effects from taking influenza and COVID-19 shots.
A CDC study from July last year found that out of the 61,390 individuals who received a Pfizer COVID-19 vaccine together with the seasonal flu shot, 58.9 percent reported experiencing “systemic reactions” in the week following the vaccination.
Among those who received a Moderna COVID-19 vaccine along with an influenza vaccine, 68.6 percent experienced “systemic reactions.”
Such dual vaccine receivers were also “slightly more likely to report any systemic reaction” compared to individuals who only received a COVID-19 jab.
“The most frequently reported systemic reactions following simultaneous administration were fatigue, headache, and myalgia (muscle pain).”
“Inability to perform normal daily activities in the week following vaccination was reported by 9519 respondents (15.5 percent) who simultaneously received Pfizer-BioNTech COVID-19 booster and influenza vaccines, and 6811 respondents (22.2 percent) who simultaneously received Moderna COVID-19 booster and influenza vaccines.”
Among the study participants, less than 1 percent required medical care. Twenty-two individuals received care at a hospital.
Hospitalized people listed the following reasons for getting admitted—excessive vomiting, supraventricular tachycardia, cardiac arrhythmia, chest discomfort, autoinflammatory disease flare, kidney infection, hypoxia, and stroke.
In an Oct. 15 preprint paper published on MedRxiv, researchers from the U.S. Food and Drug Administration (FDA) said that people aged 65 and above who received a COVID-19 vaccine together with influenza shot were found to have “an increased risk” for non-hemorrhagic stroke.
Another Oct. 15 study from researchers at Kaiser Permanente found an “elevated risk” among people aged 65 and above who received a Pfizer vaccine and influenza shot on the same day.
Meanwhile, cardiologist Dr. Peter A. McCullough recommended against following the CDC’s immunization recommendation for the fall season.
In an Oct. 20 Substack post, Dr. McCullough said that he is “not recommending COVID-19 XBB.1.5 boosters, influenza, or respiratory syncytial virus vaccines for healthy adults or children. None of these vaccines are compelling, and conditions are easily treatable.”
