Thread by @michaelzlin

Turns out there were 2 studies last week comparing J&J + J&J booster to J&J + Pfizer booster! One was NIH, as most know. The other is from Singapore and it looks like a solid study too.

Most interesting: they looked at T cells too, not just antibodies!

medrxiv.org/content/10.110…

We see again that J&J+Pfizer gave higher antibody levels and neutralizing activity than J&J+J&J, and similar to Pfizer+Pfizer. Note wide range of interdose intervals (43-71d for J&J+J&J, 11-180d for J&J+Pfizer) but Ab levels actually quite tight.

While antibodies are the first line of defense and what block you getting infected, it's essential to have T cells for avoiding late complicatinos. It's widely proposed that the Ad vaccine of J&J may elicit more T cells.

This appears true when comparing 1 dose J&J ("fully vaxxed") to 1 dose Pfizer (not fully vaxxed), but not vs 2 doses Pfizer (fully vaxxed). So in T cells too, J&J single-dose vaccine is not as good as fully vaxxed Pfizer

Regarding the question of which booster is better for T cells, J&J+J&J is worse than J&J+Pfizer in T cell responses too. So if you're J&J and wondering if you'd miss out on good T-cell stimuli with a RNA boost, it appears the answer is no; the RNA boost seems as good/better.

In summary, the number of subjects is small in each group and there's some variability in timings, but actual responses turn out with low variability in the J&J+Pfizer cases. And both antibodies and the T cell response, often mentioned but never compared, are best in J&J+Pfizer.

There was actually study way back in July (and just updated last week) comparing T cell responses between the 3 vaccines, and J&J was also inferior to 2-dose Moderna and trending to inferiority over 2-dose Pfizer. medrxiv.org/content/10.110…

I didn't make a big deal of the July result because samples were taken 24 days postvax and J&J claimed response would improve over time. But the Singapore study includes later dates too. Thus, so far no evidence J&J actually is better at T cells than full Moderna or full Pfizer

In this week's study from Singapore, median sampling times were 80 vs 94 days after J&J vs Pfizer full vaccination, and 50 vs 32 days for J&J boost vs Pfizer boost

That's plenty of time after full vax for J&J to ramp up if it needs time, and J&J booster got more time than Pfizer

So it seems at middle times (24 days) and at late times (80-94 days), 2x RNA vaccines elicited a stronger T cell response than J&J. And RNA boosters work better than J&J boosters for T cells (and much better for B cells)

As I mentioned before, the J&J booster suffers from getting cleared so that can explain some of the inferiority to RNA in the booster context, both for antibodies as discussed in the thread on the NIH study (linked below) and for T cells as discussed here

https://twitter.com/michaelzlin/status/1448335699866836993?ref_src=twsrc%5Etfw

In summary, since strong T cell stimulation was a reason for developing Ad vaccines like J&J's to begin with, what these studies are suggesting is that 2xRNA vaccines are turning out to be an even stronger way to stimulate T cells (and a much stronger way to induce antibodies)

Based on the NIH and Singapore heterologous boost studies, and the Phase 1-2 data I referred to in my thread, I came up with this guide to boosters.

The numbers are rough, but the idea is to present clearly the antibody and T cell responses of different COVID19 vaccine regimens.