Early COVID-19 symptoms may be mistaken for vaccine side-effects, study warns

LONDON — If you recently received a COVID-19 vaccine shot and feel under the weather, those may not be vaccine side-effects — you may actually have COVID-19. That’s the warning of a new study by King’s College London researchers, who find that early COVID-19 symptoms are indistinguishable from typical vaccination side-effects. In other words, don’t assume how you’re feeling is because of the vaccine, and if possible, arrange for a coronavirus test quickly.

This large-scale study encompassed 362,770 U.K. citizens vaccinated between December 2020 and May 2021. Additionally, all participants had dealt with at least one COVID-19-related symptom within their first week of vaccination. Within the entire group, 14,842 people ended up taking either a PCR or lateral flow test, with 150 testing positive for COVID-19.

Researchers used traditional machine learning models to sift through and differentiate between COVID-19 symptoms and post-vaccination side-effects among patients. They focused on three “core symptoms” specifically: fever, a persistent cough, and changes in a patient’s sense of smell.

Even AI can’t tell the difference

Even the machine learning models were unable to reliably differentiate between COVID-19 and post-vaccination symptoms. Moreover, study authors say there is virtually no way to know with 100-percent certainty that a headache, fever, general feeling of fatigue, or aches and pains are due to a coronavirus infection or not without taking a test.

The research team adds that at the time they collected this data, COVID-19 cases were generally low in the United Kingdom. Now, infections are spiking again as COVID variants spread. They caution that community transmission is even more likely today than it was a few months ago and advise everyone feeling any symptoms, post-vaccination or otherwise, to stay home.

Vaccination remains extremely important, to help protect yourself, your family, and your community from COVID-19.  However, if you do have symptoms afterwards, you should not assume that it’s just side-effects of the vaccination – although fortunately this was the most likely outcome. You should check to make sure you don’t have early COVID-19, by getting tested. This is particularly important now, when the UK is experiencing high levels of SARS-CoV-2 infection circulating in the community and particularly while we are still learning about the new variant, Omicron,” says lead study author Professor Emma Duncan in a university release.

COVID tests may save the holidays

“It takes time to develop immunity after vaccination; and if you are infected it’s important to know this – both for your own sake, so that you can receive appropriate care, and for the sake of other people, so that you can ensure you don’t pass it along to vulnerable individuals. Being tested if you have symptoms – even if you’ve been vaccinated – will help stop the spread of COVID-19,” Prof. Duncan adds.

“To identify differences in symptom types between early signs of COVID-19 and post-vaccination symptoms, we used traditional machine learning models, which considered all 28 symptoms reported in the app, and a clinical model using the three core symptoms used for testing referencing by the NHS at the time of our study,” says Dr. Liane Canas from King’s College London.

“Both the machine learning models (using all symptoms) and the clinical model (three symptoms) found it difficult to differentiate between symptoms associated with a positive test result and vaccine side effects. This is why anyone with symptoms should have a test. Ultimately, this will help us avoid spreading the virus this Christmas,” Dr. Canas concludes.

Researchers published their findings in the journal EClinicalMedicine. 

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