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Six Months of COVID Vaccines: What 1.7 Billion Doses Have Taught Scientists

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Six Months of COVID Vaccines: What 1.7 Billion Doses Have Taught Scientists

As countries race to administer coronavirus vaccines, researchers are analysing the effects while a rash of viral variants raises concern.


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After 1.7 billion doses of COVID-19 vaccinations, scientists still have some remaining questions.

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Now that six months have passed since COVID-19 vaccines were made available to the general public in the United States, scientists are collating data on their safety and effectiveness. They are finding that, just as the clinical trials suggested, the vaccines are safe and exceptionally effective at preventing illness. Some elicit dangerous side effects, but these are rare and pale in comparison to the dangers of getting COVID-19.


COVID-19 vaccines work remarkably well.

Clinical trials of tens of thousands of people demonstrated that the Pfizer-BioNTech vaccine against COVID-19 was 95% effective at preventing symptomatic illness. This was an amazing result, especially given that the vaccine relied on new technology. But clinical trials usually enroll young, healthy volunteers, so it was not clear that the vaccine would be as effective in the general population. Studies of the Pfizer-BioNTech vaccine in Israel and England and of the Sputnik V vaccine in Russia suggest that the vaccines retain this degree of effectiveness in the population at large. The vaccines are slightly less effective among residents of long-term care facilities, who as a whole are older and sicker than the general population. But they still provide some protection even for this vulnerable group. 

COVID-19 vaccines are quite effective, even against variants.

Like all viruses, SARS-CoV-2 (the virus that causes COVID-19) mutates fairly rapidly. A number of “variants of concern” have evolved over the course of the pandemic. More will probably arise before everyone in the world can...

About the Author

Heidi Ledford is a senior reporter for Nature in London. She writes about biology and medicine.

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