Add Lancet "comment" about the efficacy numbers involved with AZ

I think this doesn't touch on "the low-dose + standard-dose cohort happened to be the ones who also got the second dose much later", and overall it's not an enlightening article, but I feel given the mess that AZ has turned out to be, anything is welcome that tries to figure it out

README.md

@@ -300,6 +300,7 @@ Note that the WHO will generally be unable to make statements that their more pr
 * [mRNA vaccine-elicited antibodies to SARS-CoV-2 and circulating variants](https://www.nature.com/articles/s41586-021-03324-6) reports on immune response of recipients of Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2) vaccines and notes that activity of their serum against SARS-CoV-2 variants encoding E484K or N501Y or the K417N:E484K:N501Y combination was reduced by a small but significant margin
 * [Effectiveness of First Dose of COVID-19 Vaccines Against Hospital Admissions in Scotland: National Prospective Cohort Study of 5.4 Million People](https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3789264) shows that the Pfizer/BioNTech (BNT162b2) vaccine was associated with a vaccine effect of 85% against hospitalization at 28-34 days post-vaccination, while the effect of the Oxford/Astrazeneca (ChAdOx1) vaccine was 94%, although the age cohorts in the two vaccines were different, and the efficacy against hospitalization was similar for the two vaccines, at 81%, when looking at people over 80
 * [FDA-authorized COVID-19 vaccines are effective per real-world evidence synthesized across a multi-state health system](https://www.medrxiv.org/content/10.1101/2021.02.15.21251623v2) is a preprint that analyzes more than 60000 individuals at Mayo Clinic, dividing them into a vaccinated cohort (with Pfizer/BioNTech or Moderna) and an unvaccinated one, and retrospectively concluding there was 88.7% efficacy in preventing infection, i.e. a positive RT-PCR test at all, and hence likely also contagiousness, as opposed to just symptomatic cases, which was the benchmark of most of the vaccine trials
+* [Single-dose Oxford–AstraZeneca COVID-19 vaccine followed by a 12-week booster](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00528-6/fulltext#coronavirus-linkback-header) tries to make sense of the confusing dosing issues with the Oxford/Astrazeneca (ChAdOx1) vaccine, and provides some tentative evidence in favor of the UK choice of delaying the booster shot to 12 weeks after the initial shot
 
 
 #### Moderna (mRNA-1273)