Impact of delaying second dose of Pfizer or Moderna vaccine: modelling study
Study (published 12 May): 'Is the longer gap between jabs better?' [Spoiler: Yes, within certain criteria, which the current vaccines used in UK meet] and deductions for Covid-19 vaccination world wide.
The autumn phase 3 RCT trial results suggested, beyond all reasonable expectation, that even single dose efficacy was good. The main constraint on the world (and national) vaccination programmes was and is vaccine availability. UK JCVI decided far more lives could be saved, and hospital and critical care admissions prevented, by providing one dose to as many people as possible, particularly those at highest risk of serious Covid-19 disease outcomes, before providing second doses. For UK this has proven highly effective: well done to the JCVI for having the necessary cojones (and equivalent for the female committee members). Reinforces my pride in UK.
This study demonstrates – using modelling – that the same is likely to apply, not just in-country, but globally; that delaying the second dose worldwide will most quickly control the disease as well as reducing covid-19 mortality, SARS-CoV-2 infections, and hospital admissions due to covid-19.
Concerns about the lack of evidence for effectiveness if a second dose is delayed (beyond the arbitary 3/4 week trial protocol) are misplaced. Knowledge drawn from previous vaccines suggests that a longer gap produces a better immune response, longer-lasting immunity and greater cross-protection against variant strains. The unavoidable paucity of data on Covid-19 vaccines has generated (in nearly all other nations) an uber-precautionary approach.
But one of the current main concerns about Covid-19 is that ‘
vaccine escape' variants may arise. The more viral replication there is the more likely this is to happen. So it's important to control the disease as far as possible globally. If we vaccinate everybody in North America and Western Europe, but as vaccine escape variants arise in countries where vaccination levels are low, they will inevitably return to the vaccinated parts of the world, causing 'break-through' disease there. The international community has a vested interest in ensuring that the whole world is vaccinated as soon as possible (and this may be best achieved by a first jab and a second/booster later).
This study supports that view and raises questions about, for example, the proposed third dose (second booster) apparently planned for the UK in Autumn 2021. On balance it might be in the UK’s interests, as well as global interests, for those doses to be used in countries where they are needed more.
