Real-world Pfizer vaccine (& natural infection) efficacy against sars-cov-2 INFECTION
New Lancet paper posted today with fantastic data. papers.ssrn.com/sol3/papers.cf…
Short Thread
tl;dr 1 dose reduces infection 72% on day 21; 7d post 2nd dose, 86%; previous infection 90%
Solid study design (for observational study)
Study of 23K health care workers in England, w/ PCR testing every 2 wks + rapid tests 2x/week & PCR confirmation of + rapid tests. 35% seropositive at start.
Vaccine hesitancy was higher in previously exposed, young, women, black (much lower), poorer.
For people w/out previous exposure ("negative cohort") vaccination reduced infection 72% (21d after 1st dose) or 86% (7d after 2nd dose).
Previous exposure reduced chance of infection 90%.
This is an observational study, so, despite authors best attempts to statistically control for differences, the unvaccinated and vaccinated groups may differ in ways that affect their exposure to sars-cov-2 in either direction & this could alter efficacy estimates.
Nonetheless, I think it provides solid evidence that vaccination reduces infection substantially (70-85%) & not just disease. I wish study had shown data on viral loads so we could assess effects on infectiousness as well.
Note: Estimate from this study (72%) is a bit lower after 1st dose than I estimated for Moderna (not Pfizer, but both mRNA) in this thread (90%):
N(orth)-S(outh) gradients in Lyme disease in US
Very interesting new paper on causes of the sharp N-S gradient in Lyme disease in US
Thread journals.plos.org/plosbiology/ar…
Background
There is a huge gradient in Lyme disease incidence in the eastern US, but no simple explanation. The main tick (I. scap.) is present from ME to FL, as are key reservoir hosts (mice, shrews).
Multiple hypotheses have been proposed for this N-S gradient, including:
-a gradient in host species diversity that results in fewer ticks feeding on the most infectious hosts (called "the dilution effect")
-a gradient in selective feeding by ticks on hosts
(cont)
What is the relative risk of indoor vs outdoor dining?
COVID-19 cases are falling and indoor dining has resumed in NYC & elsewhere.
It should be possible to quantify the relative risk of indoor vs outdoor dining.
Thread nytimes.com/2021/02/12/nyr…
Many people argue that indoor dining represents a high risk for transmission of SARS-CoV-2, b/c people can't wear masks while eating, people from multiple households often sit at 1 table & at least 2 case studies show cross-table transmission is possible. jkms.org/DOIx.php?id=10…
Outdoor dining is thought to be (much) safer, due to much higher ventilation. But we still don't know the relative risk of indoor vs outdoor dining, which would be extremely valuable in determining the relative risk of re-opening these activities.
Vaccine efficacy in blocking infection & transmission
(I think) We can now estimate the (minimum) reduction in transmission from the Moderna vaccine.
Thread
tl;dr Moderna vaccine blocks >90% (87-93%) of infections & 91% (89-94%) of transmission.
*Critiques welcome!
Background
By now, everyone knows there are 4 vaccines "approved for full use" (NY Times wording) in one or more countries: Pfizer, Moderna, Sputnik 5, Astrazeneca nytimes.com/interactive/20…
These 4 have shown moderate (Astrazeneca) to very high efficacy in reducing "symptomatic" infections. bbc.com/news/world-asi…
Viral loads (& age but not symptoms) influences transmission probability, incubation period & symptomatic/asymptomatic outcome.
Fantastic new study @dr_michaelmarks. Tons to learn & haven't seen any detailed thread yet, so here's one. thelancet.com/journals/lanin…
Background
We know that transmission of SARS-CoV-2 is highly heterogeneous, with most cases infecting no one & minority of cases infecting 1 to many. How much of this is due to variation in infectiousness vs... @_akiraendo@AdamJKucharski@sbfnk@seabbs doi.org/10.12688/wellc…
differences in # & type of contacts including setting & activity (indoors, singing, temp/RH, etc.), & susceptibility of contacts? We have evidence that all of these things likely matter, but evidence linking viral loads of index patient to infection of their contacts was missing.
Novavax has shared prelim efficacy data by press release: ir.novavax.com/news-releases/…
90% overall, 50% in S Africa (60%) in HIV-.
But there's more...
@carlzimmer has written a nice story about it here:
Article makes very provocative statement - that previous exposure doesn't protect against new variant B.1.351 found initially in S africa. But where are data to support this?
Press release is vague on this. It just says this.
Hundreds of nursing home residents are dying each day due to slow vaccine rollout in SNFs.
CDC vaccine tracking page shows this huge failure.
We are failing to vaccinate the population where most deaths have occurred: nursing homes.
Thread covid.cdc.gov/covid-data-tra…
As most know, ~40% of all deaths in US (& other countries like UK) have been in nursing homes. kff.org/policy-watch/c…
As a result, nursing home residents were put, w/ health care workers (HCW), in top priority tier for vaccination. Great! But allocating vaccines to this group did NOT magically result in shots in arms. That requires huge logistical plan. Unfortunately that plan has not gone well.