Here’s a very good news story. New studies show the Pfizer-BNT vaccine works incredibly well, including against the South African variant (the most immune-evading variant known).

But the second dose is critical.

The Novavax vaccine also holds up well against the SA variant. https://abs.twimg.com/emoji/v2/... draggable="false" alt="🧵" title="Thread" aria-label="Emoji: Thread">

Real-world data from Qatar show the Pfizer-BNT vaccine is effective against the UK and South African variants, but only after the second dose.

For example the vaccine was only 39% effective against severe disease after one dose, but this rose to 97% (92-99%) after two doses.

Here’s the effectiveness by first, then second dose:

Infection:
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🇬🇧" title="Flagge des Vereinigten Königreiches" aria-label="Emoji: Flagge des Vereinigten Königreiches"> 29%, 89%
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🇿🇦" title="Flagge von Südafrika" aria-label="Emoji: Flagge von Südafrika"> 17%, 75%

Severe disease:
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🇬🇧" title="Flagge des Vereinigten Königreiches" aria-label="Emoji: Flagge des Vereinigten Königreiches"> 54%, 100% (82-100%)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="🇿🇦" title="Flagge von Südafrika" aria-label="Emoji: Flagge von Südafrika"> 0%, 100% (74-100%)
Any variant: 39%, 97% (92-99%) https://www.nejm.org/doi/full/10.1056/NEJMc2104974?query=featured_home">https://www.nejm.org/doi/full/...

In Israel, where the UK variant is dominant, real world data show the Pfizer-BNT vaccine is effective in all age groups.

Any infection: 95%
Asymptomatic infection: 92%
Symptomatic infection: 97%
Hospitalisation: 97%
Severe disease: 98%
Death: 97% (96-97%)
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00947-8/fulltext">https://www.thelancet.com/journals/...

Finally, Novavax reported 60% (20-80%) efficacy against symptomatic infection in South Africa (in HIV- people) at a time when the SA variant was dominant, and 50% efficacy in analyses specifically looking at the variant (albeit with uncertain precision).
https://www.nejm.org/doi/full/10.1056/NEJMoa2103055?query=featured_home">https://www.nejm.org/doi/full/...

Remember also that more recent data from Novavax (which are yet to be published), show that this vaccine has very high efficacy against the UK variant (86%) and even higher efficacy against the original strain (96%). https://twitter.com/drzoehyde/status/1370244946859495425?s=21">https://twitter.com/drzoehyde...

https://abs.twimg.com/emoji/v2/... draggable="false" alt="🔑" title="Schlüssel" aria-label="Emoji: Schlüssel"> Key message: the Pfizer-BNT and Novavax vaccines work extremely well, and we are incredibly fortunate to have them.

But: the second dose is critical for full protection. People should not let their guard down until they have received both doses.

Don’t forget that vaccines don’t fully block transmission. It’s possible some vaccinated people may still be able to transmit the virus to unvaccinated people.

For that reason, we need to keep various precautions in place until everyone has had the chance to be vaccinated. https://abs.twimg.com/emoji/v2/... draggable="false" alt="😷" title="Gesicht mit Mundschutz" aria-label="Emoji: Gesicht mit Mundschutz">

Addendum: it’s worth noting that for the study in Qatar, it’s not clear how many cases were detected after the first dose, but within 14 days of vaccination (when people are still developing immunity). Effectiveness after a single dose is probably higher than the figures suggest.

However, a previous study conducted in Israel looking at cases detected 14 days after a single dose of the Pfizer-BNT vaccine, clearly shows that the second dose is crucial for maximum protection. https://twitter.com/drzoehyde/status/1382604484820439043?s=21">https://twitter.com/drzoehyde...