The advice to date has, quite rightly, to get any COVID vaccine that’s available to you. For me, that’s meant a double dose of AstraZeneca, and I’m happy about that.
But as the pandemic progresses, we need to be aware that some vaccines are more effective than others. This working paper, building on one published in Nature earlier this year, looks at how ‘fractional dosing’ of the Moderna and Pfizer vaccines could reach more people more quickly.
Needless to say, we shouldn’t be in the position where people in less developed countries are getting access to vaccines much more slowly than the rest of the world. But, pragmatically speaking, this may help.
We supplement the key figure from Khoury et al.’s paper to show that fractional doses of the Moderna and Pfizer vaccines have neutralizing antibody levels (as measured in the early phase I and phase II trials) that look to be on par with those of many approved vaccines. Indeed, a one-half or one-quarter dose of the Moderna or Pfizer vaccine is predicted to be more effective than the standard dose of some of the other vaccines like the AstraZeneca, J&J or Sinopharm vaccines, assuming the same relationship as in Khoury et al. holds. The point is not that these other vaccines aren’t good–they are great! The point is that by using fractional dosing we could rapidly and safely expand the number of effective doses of the Moderna and Pfizer vaccines.
One more point worth mentioning. Dose stretching policies everywhere are especially beneficial for less-developed countries, many of which are at the back of the vaccine queue. If dose-stretching cuts the time to be vaccinated in half, for example, then that may mean cutting the time to be vaccinated from two months to one month in a developed country but cutting it from two years to one year in a country that is currently at the back of the queue.