mRNA COVID-19 Vaccines Are Effective Against Most Variants, Including Delta

The Pfizer/BioNTech COVID-19 vaccine. Image Credit: Jeppe Gustafsson/

The emergence of new variants of viruses is an unfortunate consequence of the pathogens' ability to mutate. The more they infect, the higher the chance that new variants will emerge. When it comes to the COVID-19 pandemic, the major concern is that an emerging variant will render vaccines ineffective.

New data suggests that things still look good, at least when it comes to mRNA vaccines. As reported in Nature, the vaccines from Moderna and Pfizer/BioNTech retained neutralization capacities against most variants.  

"Vaccines induce high levels of antibodies against Delta and most variants," corresponding author Professor Akiko Iwasaki, from Yale University, said in a statement. "And two shots are better than one."

Analysis shows that the vaccines bolster the immune system response against the infection. The team collected blood samples from 40 healthcare workers before, between, and after the two vaccinations doses. They then exposed the blood to 16 different variants of SARS-CoV-2, the virus that causes COVID-19. The immune responses were generally really strong, which is positive.

Among the interesting details, the immune response was much stronger after the second dose as was expected from the clinical trial. And the work confirms why there have been cases of breakthrough infections among the vaccinated.

While the spread of the Delta variant was mostly among the non-vaccinated, seeing cases among those who had received both doses raised some concerns. Could the vaccines have lost a huge fraction of effectiveness against the new variants, the delta in particular? The study says it’s not about the vaccines. The delta variant is a lot more dangerous and can more easily overcome our defenses.  

"The Delta variant is more infectious than earlier variants," co-author Nathan Grubaugh, also at Yale, added. "The high transmissibility of the variant, not its escape from our vaccine-induced immune response, best explains infections among the vaccinated."

The health workers whose plasma was studied were divided into two groups. One for those who caught the disease and one for those who didn’t. The team showed that those that had the disease, even in its original form, had a better response to the new variants, than people who hadn't. 

"Recovering from an initial infection is like getting a first vaccine shot," Iwasaki said.  

The team believes that a booster shot might deliver a similar response as having been infected without the health risks of actually catching COVID. Such shots have already been distributed in some parts of the world to at-risk populations. 


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