Pfizer’s COVID-19 vaccine works very well against the Delta variant – but only after 2 doses

Charles Muro, 13, celebrates being inoculated by Nurse Karen Pagliaro at the Connecticut Convention Center in Hartford, Connecticut on May 13, 2021.

A UK study of 19,000 people suggests Pfizer and AstraZeneca’s vaccines work well at preventing COVID-19 infections with Delta, but only if you get both doses.
After one shot, Pfizer and AstraZeneca’s vaccines were only 30-36% effective against Delta infections.
But with two shots, given two weeks to take effect, Pfizer’s vaccine was 88% effective against COVID-19 symptoms. AstraZeneca’s was 67% effective.

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A study of more than 19,000 teens and adults across the UK provides some of the first compelling, peer-reviewed, large-scale evidence that you really need both doses of two-dose vaccines in order to get good protection from the Delta variant.

The findings from Public Health England suggest that vaccine protection against Delta is still very strong when people get both shots.

However, the research, published in the New England Journal of Medicine on Wednesday, showed that just one dose of either Pfizer or AstraZeneca’s COVID-19 vaccine only protected people from symptomatic infections about a third of the time.

“It’s clear how important the second dose is to secure the strongest possible protection against COVID-19 and its variants,” UK Health and Social Care Secretary Matt Hancock said when an unreviewed preprint of the study was released back in May.

When patients were fully vaccinated, with two shots both given at least two weeks to take effect, Pfizer’s COVID-19 vaccine became about 88% effective against symptomatic COVID-19 with Delta, while AstraZeneca’s vaccine was 67% effective against it.

That is almost as good as those vaccines performed in clinical trials before the new variant was detected, but it does suggest that breakthrough infections in vaccinated people will become slightly more common, now that Delta is here.

One shot was only about 30% effective against COVID-19 symptoms with Delta
Melvin Dixon gets his second vaccine dose at a mobile COVID-19 vaccine clinic in Bridgeport, Connecticut on April 20, 2021.

This study was possible because the UK maintains a national vaccination register, and because the proportion of positive COVID-19 cases that are sequenced in the UK is far higher than in the US (around 60%, as of May 2021).

Comparing a patients’ vaccination status, their COVID-19 test results, and variant sequencing to determine whether their infection was caused by the Alpha (B.1.1.7) variant, or Delta, researchers were able to determine how well the Delta variant evaded vaccine protection.

With only one shot on board, Pfizer’s vaccine was just 36% effective against symptomatic Delta cases, while AstraZeneca’s vaccine was 30% effective, the researchers found.

Other research already suggests that the Delta variant is more contagious (easier to catch), and that may be, in part, because people who are infected tend to shed more virus while they are sick.

The researchers did not estimate vaccine effectiveness for severe disease and death in this study, but other research (and hospital …read more

Source:: Business Insider


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