COVID vaccine: 12-week dosing interval more effective than 28 days?
M3 India Newsdesk Feb 16, 2021
According to the FDA, the interval for the first and second doses is 21 days for the Pfizer-BioNTech COVID-19 vaccine. And for the vaccine Moderna COVID-19, the time between the first and the second dose is 28 days. Spacing between 2 doses of Oxford AstraZeneca COVID-19 vaccine has been about 4 weeks at many centres. In India, presently Oxford AstraZeneca COVID-19 vaccine Covishield and Covaxin has been rolled out.
So far, the use of two prescribed doses of each approved vaccine at specified intervals continues to complement the available evidence. But now, according to new evidence, the UK's method of offering a three-month gap after each dose of the Oxford AstraZeneca COVID-19 vaccine appears effective. The study, a preprint currently under review at The Lancet, is an overview of additional evidence from studies comprising 17,177 patients in the UK, Brazil, and South Africa.
In the first 90 days after vaccination, a single regular dose of vaccine offered 76% total protection against symptomatic COVID-19. However, it is not clear how long protection could last with a single dose, as there were very few cases to make any relevant decision after 90 days.
The study shows that it is the dosing interval that has the biggest influence on the potency of the vaccine, not the dosing level. These findings are in line with previous studies demonstrating greater effectiveness with longer periods between doses such as influenza and Ebola vaccine.
The study also showed that vaccine effectiveness in people with a dosing period of 12 weeks or more was 82.4 percent after the second dose (95 percent confidence interval 62.7 percent to 91.7 percent). The effectiveness was just 54.9 percent if the two doses were administered less than six weeks apart (CI 32.7 percent to 69.7 percent).
In order to screen for infections, researchers received frequent nose and throat swabs from volunteers. In avoiding asymptomatic infection, the vaccine seems to be very poor; its effectiveness improved with a longer period between doses, but there were wide confidence intervals.
The researchers find, however, that total PCR test positive cases of COVID-19 (both symptomatic and asymptomatic) decreased by 67 percent after a single dose of vaccine, raising expectations that it could have a major effect on spread by decreasing the population's number of infected individuals.
The 12-week delay between the first and second doses is obviously the best option, putting all this data together, since more patients will be covered more easily and the overall preventive benefit is stronger. The vaccine will not eliminate COVID propagation because of the low effectiveness in stopping asymptomatic infections, but will also go a long way to minimise the R value and spread because there will be much less symptomatic infections because those who are symptomatic are more contagious than others who are asymptomatic.
Implications for India
According to the Indian Health ministry recommendations, the 2nd dose of Oxford Covishield vaccine is to be administered after 28 days of the 1st dose. Vaccination campaigns targeted at vaccinating a significant majority of the population with a single-dose followed by a second dose provided after 3 months is an appropriate disease-reduction technique which could be ideal for a pandemic vaccine to be phased out while resources are reduced in the short term.
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Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.
The author, Dr. Monish S Raut is a Consultant in Cardiothoracic Vascular Anaesthesiology. His area of expertise is perioperative management and echocardiography with numerous publications in various national and international indexed journals.
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