The largest real-world analysis of “natural” immunity shows a previous covid infection may protect more against the delta strain than the two-dose Pfizer vaccine. Separately, data show blood clot risks from covid outweigh clotting risks from vaccines.
People who recovered from a bout of Covid-19 during one of the earlier waves of the pandemic appear to have a lower risk of contracting the delta variant than those who got two doses of the vaccine from Pfizer Inc. and BioNTech SE. The largest real-world analysis comparing natural immunity — gained from an earlier infection — to the protection provided by one of the most potent vaccines currently in use showed that reinfections were much less common. The paper from researchers in Israel contrasts with earlier studies, which showed that immunizations offered better protection than an earlier infection, though those studies were not of the delta variant.
In updates on vaccine side effects, Covid-19 patients face a much higher risk of developing blood clots than those vaccinated with AstraZeneca Plc or Pfizer Inc.’s shots, according to a large U.K. study. For every 10 million people who receive the first dose of AstraZeneca, about 66 more will suffer from a blood-clotting syndrome than during normal circumstances, according to the study published in the British Medical Journal. This figure compares with 12,614 more incidences recorded in 10 million people who have tested positive for Covid-19.
The largest real-world study of a COVID-19 vaccine to date shows that Pfizer/BioNTech’s shot is safe and linked to substantially fewer adverse events than SARS-CoV-2 infection in unvaccinated patients. A team led by researchers from the Clalit Research Institute in Tel Aviv, Israel, and Harvard University matched vaccinated Israelis 16 years and older (median age, 38) with similar but unvaccinated people infected with SARS-CoV-2 from Dec 20, 2020, to May 24, 2021. They then derived risk ratios (RRs) and risk differences 42 days after vaccination (short- to medium-term) using the Kaplan-Meier estimator.
As the delta variant spreads in the U.S., updated findings from the Centers for Disease Control and Prevention show that the efficacy of the covid vaccines among essential workers dropped from 90% to 66%. Separately, Johnson & Johnson reports big antibody response boost from a second shot.
The effectiveness of Covid-19 vaccines at preventing infection fell in one study of U.S. frontline workers from roughly 90% to 66% as the Delta variant emerged and became dominant in the country, an updated report from the Centers for Disease Control and Prevention released Tuesday indicated. The study, known as HEROES-RECOVER, includes more than 4,000 health care workers, first responders, and other frontline workers in eight locations across six states, all of whom have been tested weekly for infection with SARS-CoV-2. More than 4 in 5 were vaccinated, and the vast majority of them received the mRNA vaccines from either Pfizer-BioNTech or Moderna.
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