Single-dose vaccine may be effective for Covid-19 survivors

Pfizer-BioNTech COVID-19 doses are prepared at a vaccine outreach clinic at Mt. Zion Baptist Church in Kalamazoo Michigan on Tuesday

'In South Africa, where the B.1.351 lineage is prevalent and 800 participants were enrolled, nine cases of COVID-19 were observed, all in the placebo group, indicating vaccine efficacy of 100%,' the company said.

Some 100 people aged 80 to 96 received their vaccine doses three weeks apart, before the United Kingdom adopted a policy of stretching the time between jabs to 12 weeks. Six of the nine cases were confirmed to be of the South African variant. And it appeared to be fully effective against the worrying B.1.351 variant of the virus, which is the dominant strain circulating in South Africa and which researchers feared had evolved to evade the protection of vaccines, the companies said.

"Both of these revisions positively impact the supply of Moderna Covid-19 vaccine, which will help provide more vaccine doses to communities and allow shots to get into arms more quickly", said Dr Peter Marks, director of FDA's Centre for Biologics Evaluation and Research. It did not list the side effects for the younger group, but the adult trial's side effects generally were mild to moderate and included injection-site pain, headaches, fever and fatigue.

"Our findings extend those from smaller studies reported elsewhere and support a potential strategy of providing a single dose of vaccine to persons with a confirmed prior history of coronavirus infection, along with two doses for people not previously infected", said Susan Cheng, Associate professor at the Cedars-Sinai Medical Centre in California, US.

The study found cellular T cell responses developed in 63% of the older people given two doses of the Pfizer jab.

The workers also underwent antibody tests to gauge the response of their immune systems to the vaccinations. More than 300 cases of the South African variant have been detected in more than 25 USA states and jurisdictions, according to federal data.

"The antibody levels were so high that they'd gone above the thresholds so they had to dilute them". And the combination of having very high levels of antibodies and persistent levels of protection are the recipe for a very long level of protection against these variants, ' Hensley added.

More doses of Moderna's COVID-19 vaccine could soon be available after the FDA revised how many doses could be available per vial, up to 50% more.

There have been doubts raised about the effectiveness of vaccines on variants. Johnson & Johnson is planning its own pediatric studies.

The vaccine remains more than 91% effective against disease with any symptoms for six months, the companies said in a statement.

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