With the virus running amok in the country and vaccines in short-supply, the U.K. is attempting an untested strategy of delaying the second dose of both AstraZeneca and Pfizer vaccine even in the absence of data from large trials. The intent is to rapidly but partially protect more individuals who are at risk.
With the U.K. regulator on December 30 granting an emergency use authorisation for AstraZeneca’s COVID vaccine, three vaccines have now been greenlighted for use even before a full approval is granted.
Unlike the mRNA vaccine platform of Pfizer and Moderna vaccines, AstraZeneca uses a weakened version of a common cold virus (adenovirus) that carries the genetic material of the spike protein to elicit an immune response. Requiring only 2-8 degree C for transport and storage, the vaccine can be administered in existing healthcare settings, allowing rapid deployment.
Together with the cost, which is much cheaper than the mRNA vaccines, this is particularly critical to help end the pandemic in the global south. The emergency use approval by the U.K regulator — Medicines & Healthcare products Regulatory Agency (MHRA) — makes it easier for a similar approval of the vaccine tested and manufactured here.
EMA yet to approve
While the U.K. regulator has granted emergency use approval, the European Medicines Agency, on the same day, clearly said that “additional scientific information on issues related to quality, safety and efficacy of the vaccine is deemed necessary” to give a similar nod.
While published results show only 62% efficacy when two full-strength doses are administered four weeks apart, the U.K regulator has relied on unpublished data showing efficacy increasing to 73% 22 days after the first dose when the second jab was delayed. A majority of the participants in the phase-3 trial in the U.K. included in the primary analysis received the second dose more than nine weeks after the first.
Delaying the second dose
Based on this information, the regulator has permitted the second dose to be administered 4-12 weeks after the first jab. The intent is to maximise the benefits of the vaccine by stretching the time between two doses to allow more people to get vaccinated, an untested strategy to rapidly but partially protect more individuals who are at risk.
With the virus running amok in the country, the U.K. has revised its policy to delay the second dose of Pfizer vaccine too despite no trial data to support this; the second Pfizer jab is originally scheduled three weeks after the first. While the regulator says there is 89% short-term protection from day 14 after the first dose, Pfizer insists that there is “no data to demonstrate that protection after the first dose is sustained beyond 21 days”. Two doses of both vaccines complete the course and prolong the duration of protection.
More trials needed
If the pandemic forced scientists, companies and regulators to quickly make available safe and efficacious COVID vaccines, delaying the second dose to maximise the benefits of the vaccine is altogether a new strategy.
The untested approach might probably be appropriate for U.K., which is facing the brunt of the virus, as a desperate measure. Since delaying the second dose appears to be increasing the efficacy, and as U.K. has approved a delayed second dose, India should carry out large trials to test this.
Science Chronicle 