I’ve been arguing that we should delay the second dose (or at least not hold back first doses) in order to hit the virus hard and inoculate more people on the first dose. I wrote:
We should vaccinate 6 million people with first dose NOW. It is deadly cautious to hold second dose in *reserve*. Supply chain will be ok and the exact timing of the second dose is not magical and likely not critical. In the accidental low-dose, standard-dose regime for the AZ vaccine, people got the second dose 7 to 8 weeks after the first dose and that was the 90% efficacious regime. [A different vaccine obviously but ] Exact timing of the second-dose does not seem critical, although everyone should get a second dose.
Today epidemiologist Michael Mina and writer Zeynep Tufekci, who has been ahead of the curve on much of the discussion, make the case even more strongly in the NYTimes:
First, the science. While the vaccine trials were designed to evaluate a two-dose regimen, some immunity might be acquired before a second dose is administered. We know, for instance, that a Covid-19 infection appears to yield protection for at least six months. While infections are not vaccinations, and while we need more data on this, it’s plausible that the immunity gained from a vaccination may turn out to be even stronger than what comes from an infection. The reason we do a second — booster — vaccination is that these later doses help to solidify immune memory, in part by giving extra training to the cells that produce antibodies, a process called affinity maturation. But this process begins with the single dose, and the evidence collected between the time of the first and second doses in tens of thousands of people in the Phase 3 trials suggests that the level of affinity maturation may provide enough protection to meet the standards we have set for vaccine approval during this pandemic even without the second dose.
While we know that the single dose can protect against disease, we don’t yet know how long this immune protection will last, and at what level. However, there is no rule that says that vaccines must be boosted within weeks of each other. For measles, the booster dose is given years after the first dose. If the booster dose could be given six months or a year after the first dose, while maintaining high efficacy before the second dose, that would allow twice as many people to get vaccinated between now and later next year, accelerating herd immunity — greatly helping end the crisis phase of the pandemic in the United States.
… we should begin immediate single-dose trials, recruiting volunteers from low-risk populations who are first in line for the vaccinations. For example, among health care workers protective equipment works, rates of infection among this group have fallen sharply and severe disease is much more rare.Younger essential workers without risk factors are less likely to be severely affected if they are exposed since this disease’s impact rises steeply with age. Just as tens of thousands of people volunteered for the earlier vaccine trials, many may well volunteer to test a placebo against a second dose, allowing us to quickly ascertain questions of durability and effectiveness of the single dose.
Two additional points. First, mix and match, as I argued earlier, may be beneficial:
…we could mix and match vaccines. The UK will run a trial on this question. Mix and matching has two potentially good properties. First, mix and matching could make the immune system response stronger than either vaccine alone because different vaccines stimulate the immune system in different ways. Second, it could help with distribution. It’s going to be easier to scale up the AZ vaccine than the mRNA vaccines, so if we can use both widely we can get more bang for our shot.
Second, an economics issue. If we want Pfizer and Moderna on board we need to pay them not just to run the clinical trials but to be happy with potentially selling half as many doses. Incentives matter.