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What do we know about the side effects of flu shots compared to the side effects of COVID-19 vaccines?


by Health Desk
Published on October 1, 2021

What our experts say

Approved COVID-19 vaccines and influenza vaccines (flu shots) have been rigorously tested for safety and efficacy. Side effects for both types of vaccines are typically minor, with more serious complications being rare. Health recommendations are for everyone who is eligible to get these life-saving vaccines, with very few exceptions (e.g. people who are too young, people with medical conditions, etc.).

Claims that data from the Vaccine Adverse Event Reporting System (VAERS) shows worse side effects for COVID-19 vaccines compared to flu shots should be considered with caution. As an open system where healthcare providers, vaccine manufacturers, and the public voluntarily submit reports, VAERS information is unverified and may be incomplete, inaccurate, coincidental, or biased. In fact, VAERS includes a disclaimer that "reports alone cannot be used to determine if a vaccine caused or contributed to an adverse event or illness" and that there are limitations in using the data for scientific purposes.

In addition, VAERS data should be used with caution when comparing adverse events between two different diseases. This is because 1) there are underlying factors influencing people, and 2) VAERS only gives us absolute numbers of events reported when the denominators (amount of people being vaccinated) differs for each type of vaccine.

For instance, on average, about 65.1% of the U.S. population has received at least one dose of a COVID-19 vaccine, whereas in the last flu season, about 51.8% of the U.S. population received a flu shot. The more people that get a vaccine, the more likely there are to be reports on it. If a vaccine requires two doses rather than one, that increases the number of opportunities for an undesired event to take place associated with the vaccine, regardless of whether it was caused by it. Finally, if a certain adverse event is increasing in general, there’s likely to be an increase of it in VAERS as well. Since the start of the COVID-19 pandemic, the rate of many diseases and health conditions has gone up, which could be factoring into the data as well.

When it comes to the differences in COVID-19 vaccines and flu vaccines, some health experts have pointed out that approved COVID-19 vaccines tend to have higher efficacy rates for preventing hospitalization and death compared to flu shots. Flu shots are updated annually based on seasonal circulating strains of the virus and clinical trials are no longer conducted every time, but a study published 2017 shows flu shots can cut the risk of death in healthy children by about 65%.

Additionally, flu shots and COVID-19 vaccines are different types of vaccines for different diseases, so differences in side effects and effectiveness are not unexpected and should not be used as the deciding factor for whether to get either vaccine. A common saying is that this would be like comparing apples to oranges; the comparison does not make sense because of substantial differences in the items being compared. Flu shots are known to come with slightly less side effects than the COVID-19 vaccines, but that is because of the nature of how they are designed and what they are preventing. The COVID-19 vaccine is also known to come with slightly less side effects than other vaccines, such as shingles.

Health recommendations currently include a wide range of vaccines with different potential side effects (e.g., tetanus, measles, polio, shingles), because these vaccines have independently been determined to be safe and effective. Rather than comparing different vaccines side by side, medical and public health experts carefully check that each vaccine individually has benefits (e.g. saving lives, preventing serious health impacts that could be long-term or permanent) that far outweigh the potential side effects before granting approval and including the vaccine in official health recommendations.

Both COVID-19 vaccines and flu shots are recommended, regardless of any differences in side effects and efficacy. COVID-19 vaccines cannot prevent deadly influenza cases and flu shots cannot prevent deadly COVID-19 cases, so health experts recommend getting both types of vaccines rather than comparing the two. Both COVID-19 vaccines and flu shots are important for saving lives.

Context and background

Vaccine hesitancy is a concern because approved vaccines are important for saving lives. Misleading information about approved vaccines is dangerous, because it can make people more hesitant to get vaccinated. Claims about vaccine side effects should be carefully verified before being shared or used for decision-making, by ensuring data sources are reliable and appropriate for how the information is being analyzed. When in doubt, please consult a health expert.

Used with permission by Health Desk, a public health hub that explains emerging COVID-19 science

This article was written and edited by the Tayo editorial desk and has been reviewed by an independent panel of subject matter experts.

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