published at statnews.com // written by Helen Branswell Feb. 2, 2021
Scientific teams around the world have developed successful Covid-19 vaccines in incredibly short order. In a feat that even a couple of years ago would have seemed completely out of reach, vaccines to protect against the new disease were being used before the first anniversary of the disclosure that a new threat existed. This is truly extraordinary.
In the United States so far, three vaccines have been issued emergency use authorizations — green lights from the Food and Drug Administration to be put into use, even though they have not yet been fully licensed.
A vaccine developed by the partnership of Pfizer and German-manufacturer BioNTech came first in mid-December, followed closely by one developed by Moderna with assistance from the National Institute of Allergy and Infectious Diseases.
In late February came a third. Janssen Pharmaceuticals, the vaccine division of Johnson & Johnson, secured an emergency use authorization for its one-dose vaccine. The vaccine was seen as a potential game-changer. It doesn’t require the fussy cold-chain needed to keep the Pfizer and Moderna vaccines from spoiling. It is cheaper, both on a per-dose basis and because only one dose is needed. Plus it was thought a one-and-done option might entice some people who couldn’t easily get two doses to roll up their sleeves.
But since the J&J vaccine’s arrival on the scene there have been a number of challenges. A production snafu in the hands of a contract production company contaminated 15 million doses, which had to be destroyed. And in mid-April, the FDA and CDC recommended states pause use of the vaccine as they investigate whether the vaccine triggers a rare but serious side effect — the development of diffuse blood clots, even though the few individuals who developed the condition had low platelet levels.
Please note that in the initial rollout of vaccine, individuals may not be offered a choice of which vaccine they want. Supplies are too scarce. The vaccine available at the place where you are being vaccinated is the one you’ll get.
The Pfizer and Moderna vaccines are made using messenger RNA, or mRNA, a technology that delivers a bit of genetic code to cells — in effect, a recipe to make the surface protein (known as spike) on the SARS-2 virus. The proteins made with the mRNA instructions activate the immune system, teaching it to see the spike protein as foreign and develop antibodies and other immunity weapons with which to fight it.
The J&J vaccine uses a different approach to instruct human cells to make the SARS-2 spike protein, which then triggers an immune response. It is what’s known as a viral vectored vaccine. A harmless adenovirus — from a large family of viruses, some of which cause common colds — has been engineered to carry the genetic code for the SARS-2 spike protein. Once the adenovirus enters cells, they use that code to make spike proteins. J&J employed this same approach to make an Ebola vaccine that has been authorized for use by the European Medicines Agency.
The Pfizer vaccine has been authorized for use for people aged 16 and older, though the company has recently asked the FDA to change the label to allow children 12 and older to be vaccinated. Moderna’s has been cleared for use in people 18 and older, though the company is now testing its vaccine in 12- to 17-year-olds. J&J’s vaccine has been tested in people 18 and older, and that’s who it was authorized for. Until testing in children and younger teens is conducted, this vaccine won’t be available for use anyone under 18 years old either.
The Pfizer and Moderna vaccines have shown astonishing — and essentially equivalent — degrees of efficacy, at least in the early stages after vaccination.
The Pfizer vaccine showed efficacy of 95% at preventing symptomatic Covid infection after two doses. The vaccine appeared to be more or less equally protective across age groups and racial and ethnic groups …
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