25/ One dose is good enough against the original strains of the virus (B VIC01).
But you really need two doses of vaccine against the B.1.1.7 and B.1.351 variants.

26/ https://www.sciencedirect.com/science/article/pii/S0092867421002981
See Fig 4:
Persons who received only one dose of Pfizer or Moderna vaccine had lower and in some cases undetectable neutralization of the B.1.1.7, P1 & other variants of concern even though they had activity against the original strains of SARS-CoV-2.

27/ Among those who received only one dose of Pfizer or Moderna vaccine, none had neutralizing activity against B.1.351 EXCEPT for those who had previously been infected or had a significant exposure.

28/ https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(21)00068-9/fulltext
Serum taken from people who received TWO doses of Pfizer vaccine had lower neutralizing efficiency against SARS-CoV-2 virus with the E484K EEK immune-evasion mutation versus against the original strains of the virus.

29/ Vaccines should induce the highest neutralizing antibody titers possible to maximize protection against SARS-CoV-2 mutation and evolution to evade vaccine-induced immune responses.

30/ In summary, we have evidence that neutralizing antibody levels after 1st dose of Pfizer and Moderna vaccines are NOT very effective against B.1.1.7 (now the dominant variant in the U.S.) or the B.1.351 variant.

31/ Moreover, we know that 2nd doses of vaccine are necessary to provide a significant boost to neutralizing antibody levels.

Here’s the data on the Pfizer vaccine: https://twitter.com/celinegounder/status/1358443839640502272?s=20

32/ Studies have shown that 2nd doses of Moderna vaccine boost antibody levels significantly: https://twitter.com/celinegounder/status/1358444252875915264?s=20

33/ Here’s another study showing that 2nd doses of Moderna vaccine boost antibody levels significantly (day 29 = day of 2nd dose):
https://www.nejm.org/doi/full/10.1056/NEJMc2103916

34/

35/ Here’s the publication they’re referring to: https://www.nature.com/articles/s41577-021-00544-9
This op-ed really got me rethinking my opinon: https://twitter.com/celinegounder/status/1378081650580586504

36/ But it’s important to note that the this is an op-ed published in a scientific journal, not published research. https://www.nature.com/articles/s41577-021-00544-9
This isn't based on modeling or empirical evidence. And they make numerous assumptions.

37/ As I’ve argued above, there are very REAL (not theoretical) risks of selecting for new variants with a 2nd dose delay strategy.

38/ We may be observing the benefits of delaying 2nd doses and spreading out first doses now, in the short term. We won't observe the harms of delaying 2nd doses until later, in the longer term.

39/ Here’s an analogy from the world of TB & HIV. For many years, experts debated when to start treatment for HIV in patients who had both TB and HIV.

40/ It was thought that you should treat a patient for TB x months before starting treatment for HIV because patients with TB could develop immune reconstitution inflammatory syndrome (IRIS) if they got antiretroviral therapy and their immune systems got stronger.

41/ This was a real short-term harm of early treatment for HIV in patients with TB and HIV.

42/ But when clinical trials looked at this formally (e.g. the STRIDE Study https://clinicaltrials.gov/ct2/show/NCT00108862), we realized that there was significant mortality benefit to starting treatment for HIV early.

43/ Just as we’re seeing the short-term upside of delaying 2nd doses… the TB docs who treated these patients only saw the short-term downside (IRIS) of early HIV treatment. They didn't see the long-term downside of dying from AIDS.

44/ I worry about complicating vaccine rollout. The President’s Emergency Plan for AIDS Relief https://www.state.gov/pepfar/  was in part successful in scaling up treatment for HIV in sub-Saharan Africa was that it was based on simple protocolized treatment algorithms.

45/ The more complicated you make a big public health program, the harder it is to execute. COVID vaccination is the biggest public health program the U.S. has ever taken on.

46/ I disagree with this. The assumption is that people would not die or be harmed by dose delay. We don't know that.

47/ This was also the argument made about letting patients try experimental drugs during the early years of the AIDS pandemic or for loosening the FDA approval process for HIV treatments.

48/ Even some of the most strident HIV activists like @PeterStaley and @TAGTeam_Tweets Mark Harrington understood the importance and necessity of clinical trials to answer these kinds of difficult questions. https://www.justhumanproductions.org/podcasts/e10-dr-tony-fauci-from-one-pandemic-to-another

49/ And so the answer to the question: to delay 2nd doses of the Pfizer and Moderna COVID vaccines? Or not to delay?

50/ It’s a decidedly un-Shakespearean one.

Fear of death makes us all cowards, but we do NOT become weak from study and thought.

We must not delay 2nd doses without first doing the research to support it.