Thread by @michaelmina_lab

Thread

This new piece in @nytimes shows great benefits of vax to reduce disease

BUT the evaluation of Vax to reduce cases (ie: 6x higher cases in unvax’d) relies on data that is fundamentally flawed by the @CDCgov’s policies - to not test if vax’d

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nytimes.com/interactive/20…

If we have a National test policy that differs by vaccination status - such that the CDC put out stating to not test once vaccinated, then regardless of the biology, policy will drive detected cases down among vaccinated, regardless of whether they are truly lower.

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This immediately makes interpretation of reported cases between the two groups uninterpretable.

Instead, what we need in the US is a robust mechanism to do ongoing random surveillance testing to actually identify vax effects to cut virus acquisition and transmission

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Luckily, such data do exist for the UK where they have a very robust random testing process to track the virus.

Unfortunately, that data do not show nearly as rosy a picture for the benefits of vax to cut transmission after about 3 months post vax.

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In a very nice paper by Tim Peto, the group looked at over 100,000 index cases and the impact of vax on alpha or delta infections in contacts.

While the vax was effective to cut spread, it’s benefits diminished quickly - over 3 months

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medrxiv.org/content/10.110…

After about 14 weeks post vaccination in the index case, there was no benefit on reducing onward transmission detected among contacts with the adenovectored vax and about a 20% reduction in the mRNA vaccinated

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Of note, the numbers mentioned above were for vax resistance to transmission at 14 weeks post vaccination in the index case with Delta. Efficacy appeared stronger for alpha, but this is not relevant now that Delta is majority of cases.

Additionally, there is better news too!

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If we look at the data not by time since vaccination of the index cases but rather time since vax of the contacts, we see a rosier picture. By 14 weeks post vax, contacts had about half the chances of testing PCR positive compared to unvax’d.

Unfortunately though…

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Unfortunately the trend was continuing towards a reduction in benefit for transmission reduction over time. Which is why many are advocating for widespread boosters.

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What this paper shows is that while there is vax benefit to reduce spread, spread among vax’d is not rare

When we consider that Delta may be more than 2x as transmissible as earlier variants, transmission of Delta among vax’d may be greater than Wuhan strain in unvax’d

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So to sum, get vax’d bc it will reduce disease!

But don’t consider breakthrough cases rare and don’t be disillusioned and think that just bc you have a breakthrough case it means the vax failed. Not true

Breakthrough transmission is common - vax are best to reduce sickness

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