Home Life & Style Pfizer vaccine: Latest study reveals jab only 46 percent effective against Delta...

Pfizer vaccine: Latest study reveals jab only 46 percent effective against Delta variant



The Delta variant, which was first identified in India, is now by far the most dominant strain of coronavirus in the UK and other parts of the world. The Pfizer vaccine may be less effective than the Moderna’s jab against the Delta variant of the coronavirus, according to a new study.

A new study from Mayo Clinic has found the Pfizer vaccine is only 42 percent effective against the Delta variant as opposed to the Moderna jab which is 76 percent effective.

The study took place in Minnesota, USA which saw a surge in Covid cases resulting from the Delta variant which grew from 0.7 percent prevalence in May to more than 70 percent in July.

The study, which has not been peer reviewed yet, was published in MedRxiv and collated data from around 25,000 Minnesotans in the period from January to July.

It was found the vaccines began to dip in effectiveness as the year progressed and as the variant become dominant.

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Researchers wrote in the paper: “Although clinical trials and real-world studies have affirmed the effectiveness and safety of the FDA-authorized COVID-19 vaccines, reports of breakthrough infections and persistent emergence of new variants highlight the need to vigilantly monitor the effectiveness of these vaccines.

“Here we compare the effectiveness of two full-length Spike protein-encoding mRNA vaccines from Moderna and Pfizer/BioNTech in the Mayo Clinic Health System over time from January to July 2021, during which either the Alpha or Delta variant was highly prevalent.

“Both vaccines were highly effective during this study period against SARS-CoV-2 infection, however in July, the effectiveness against infection was considerably lower for Moderna vaccine with an even more pronounced reduction in effectiveness for the Pfizer.

“Notably, the Delta variant prevalence in Minnesota increased from 0.7 percent in May to over 70 percent in July whereas the Alpha variant prevalence decreased from 85 percent to 13 percent over the same time period.”


The effectiveness of Moderna’s vaccine against infection had dropped to 76 percent in July – when the Delta variant was predominant, said Dr Venky Soundararajan of Massachusetts data analytics company nference, who led the Mayo study.

She added: “While both vaccines remain effective at preventing Covid hospitalisation, a Moderna booster shot may be necessary soon for anyone who got the Pfizer or Moderna vaccines earlier this year.”

Dr Anthony Fauci, the nation’s top infectious disease expert, warned last week that he feared a vaccine-resistant variant could form in the near future if the virus continued to spread.

Data from the Centers for Disease Control and Prevention finds that vaccinated people who contract the Delta variant release similar viral loads to unvaccinated people, meaning they may be just as able to spread the virus.

The Delta variant being able to bypass the existing vaccines also confirms what many feared, that the virus could potentially mutate to a point where it can bypass vaccines.

Last month, Pfizer published data showing its vaccine’s efficacy drops to 86 percent after six months.

Almost 40 million people in the UK have now received both doses of the coronavirus vaccine.

Everyone over the age of 18 is now eligible for a Covid jab.

In total, 88 percent of the UK public have been given at least one dose of the vaccine.

If you develop a new cough, a high fever, or a loss of smell or taste, you should book a Covid test as soon as possible.


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