Symptoms, vaccine efficacy …: what you need to know about the delta variant

Although vaccines provide effective protection against the virus, they are not 100% effective.

PSeveral new symptoms emerged when the alpha variant was supplanted by the delta variant in the UK, there now appears to be a difference between the symptoms reported by people who have been vaccinated and those who have not.


In people who have not been vaccinated, the five most common symptoms are: headache, sore throat, runny nose, fever, and persistent cough. These correspond to the symptoms of the delta variant, which has become the dominant strain in the UK (and also in Belgium).

For people who have received a dose of the vaccine, the most common symptoms are headache, runny nose, sore throat, sneezing and a persistent cough. Not only has the order changed, but the fever is no longer in the top 5 and has been replaced by a new symptom: sneezing.

Those who have been fully vaccinated currently report headache, runny nose, sneezing, sore throat, and loss of smell as the most common complaints. Again, the order is different. And this time, not only the fever but also the persistent cough disappeared from the list. The loss of smell, a symptom of the original strain of the coronavirus, reappears.

Vaccine efficacy

The efficacy of Pfizer and Moderna’s vaccines against covid infection has fallen from 91% to 66% since the delta variant became dominant in the United States, according to data released Tuesday by U.S. health officials.

This data comes from a study of thousands of healthcare workers and hospital workers in six states to examine the performance of vaccines in real conditions. Participants are tested weekly for both symptomatic and asymptomatic infections.

Between December 2020 and April 2021, the effectiveness of vaccines in preventing infection was 91%, according to data released by the Centers for Disease Control and Prevention (CDC), the country’s main federal public health agency.

But over the weeks when the Delta variant became dominant, that is, when it was responsible for more than 50% of the cases according to the sequencing, the efficiency fell to 66%.

The authors of the study warn, however, that this decline may not be caused only by the Delta variant, but also by an efficiency eroding over time.

“Although these interim data suggest a moderate reduction in the effectiveness of covid vaccines in preventing infection, the fact that the reduction in infections remains at two-thirds underscores the continued importance and benefit of vaccination,” write the authors of this work.

Predominance of the variant in contaminations

During the bulletins that Sciensano issues for the surveillance of the spread of the virus in Belgium, the Institute also examines the presence of the delta variant in us. According to the last report dated August 27, the delta variant represents 99.4% of the samples sequenced in the baseline surveillance carried out over the period from August 9 to 22.

As regards the other variants over this same period, the alpha and gamma variants both represented 0.1% while the beta variant, 0%.


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