Pfizer's Covid vaccine is only 42% effective against Indian 'Delta' variant while Moderna's jab is 76% effective, Mayo Clinic study suggests

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The current crop of COVID-19 vaccines may not be as effective against the Indian 'Delta' variant compared to the original strain of the virus, a new study suggests.

Researchers from the Mayo Clinic in Rochester, Minnesota, found that the Pfizer-BioNTech vaccine - the most commonly used shot in the U.S. - was only 42 percent effective against infection in July.

Meanwhile, the Moderna vaccine was only 76 percent effective.

The highly contagious Delta variant is the dominant strain in the U.S., and there are fears that it has a unique ability to cause breakthrough cases among those who are fully vaccinated.

There is also growing conversation about booster shots being made available for Americans in the near future to continue immunity against virus variants. 

Effectiveness of the Moderna (yellow) and Pfizer (blue) COVID-19 vaccines began to drop in June and July as the 'Delta' variant became more prevalent. Moderna had an effectiveness of 76%, while Pfizer's vaccine was 42% effective.

For the study, published on pre-printer server - meaning it has not yet been peer review - the team gathered data on more than 25,000 Minnesotans from January to July. 

While the vaccines remained about as effective as advertised, around 90 percent, for the first six months of the year, their effectiveness began to dip in June. 

However, the efficacy largely dropped in July as the variant took hold in the United States.

The change in vaccine effectiveness corresponds with a massive surge in the prevalence of the Delta variant in Minnesota, growing from 0.7 percent prevalence in May to more than 70 percent in July.

Meanwhile, the Kent 'Alpha' variant, the previous dominant strain in the U.S., decreased in prevalence from 85 percent to 13 percent over the same time period. 

Even despite a rise in breakthrough infections, the vaccines were still effective in preventing hospitalizations and severe cases from the virus, with both having a hospitalization rate of under 25 percent. 

While breakthrough cases became more common in July, the rate of hospitalization remained low, with both being more than 75 percent effective

The rise of Delta variant prevalence in Minnesota, from 0.7% prevalence in May to more than 70% in July, correlates with the drop in effectiveness of the vaccines (above)

Unvaccinated people also still made up a vast majority of cases.

Still, vaccinated people being able to contract the virus is a worrying prospect for health officials.

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.    

While the risk is minimal, some vaccinated people still may be hospitalized, suffer long term negative effects, or even die, from COVID-19.

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.

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. 

But booster shots could soon rollout for Americans to enhance immunity to the virus and protect against these more resistant variants. 

NBC News reported on Wednesday that the U.S. Food and Drug Administration (FDA) planned to approve third doses for immunocompromised Americans.

It is a change of tone from other health officials in recent weeks, including National Institute of Health Director Dr Francis Collins, who said last week booster shots were not necessary.  

Currently, there are three available Covid vaccines in the United States.

The Pfizer vaccine is the most popular, having been used 197 million times since it received FDA emergency use authorization (EUA) in December 2020.

The Moderna vaccine, which was also given EUA in December, has been used more than 140 million times.

Only one single dose vaccine is available in the U.S. -  the Johnson & Johnson vaccine - which has been used 13.7 million times.

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