Saturday, January 16

What is the scientific basis for delaying the second dose of the Covid vaccine? | World News

ORK’s health Officials have decided To delay the administration Of second doses Of Covid-19 vaccines and even allow the combination Of doses from different manufacturers, raising international concern. What is the scientific justification for this decision?

Why has the UK decided To widen the gap between the first and second doses Of vaccine?
The original plan was To Offer priority groups an initial injection Of vaccine, followed by a second dose three weeks later. But a rapid increase in the number Of Covid-19 cases, combined with the emergence Of a more transmissible variant and uncertainty about the supply Of vaccine sTocks, led the Joint Committee on Vaccination and Immunization (JCVI) To consider other options.

He calculated that he could get a first injection Of vaccine in more arms faster if he delayed giving the second dose To 12 weeks later, at which point many more doses Of vaccine are expected To be available. ” This is very likely To have a greater public health impact in the short term and reduce the number Of preventable deaths from Covid-19,” said a JCVI statement.

Isn’t this the same strategy proposed by Tony Blair?
The former prime minister proposed giving as many people as possible a single dose Of a Covid vaccine rather than holding sTocks To allow for a second prick, which is slightly different from what is happening now.

The JCVI has emphasized that everyone will receive a second puncture, it will only arrive later than originally planned, with a maximum interval Of 12 weeks between the first and second doses. This second “boost” dose is likely To strengthen and optimize the duration Of the immune response, resulting in longer-term protection.


Why are some scientists concerned?
Mainly because the impact Of extending the two doses has Not been proven in clinical trials. It has also Not given a first dose Of the Pfizer / BioNTech vaccine, followed by a second dose Of the Oxford / AstraZeneca vaccine, or vice versa, which the JCVI advises only in “exceptional circumstances”, for example, if a second dose is Not Received. Of the original vaccine. Not available.

The main risk is that people’s immunity level drops before they receive their second dose, putting them at risk Of contracting Covid-19, although this risk would still be lower than if they had Not Received any vaccines and would increase when they finally did. Received it. his second shot. Pfizer cautioned that its trial only investigated giving two doses 21 days apart, much less than 12 weeks.

However, a consensus statement from the British Society Of Immunologists said delaying the booster dose by eight To nine weeks was unlikely To make much Of a difference in the long run.

What about mixing and matching dosages from different manufacturers?
This has also Not been proven in clinical trials, although scientists from the UK and Russia are investigating whether the combination Of injections Of the Oxford / AstraZeneca and Sputnik V vaccines could result in better protection than two doses Of the same.

Theoretically, combining doses from different manufacturers should trigger an effective immune response, since almost all Covid-19 vaccines being developed are based on the same viral “spike” protein, even if it is presented To our bodies from slightly different shapes. .

Could other countries follow the United Kingdom?
Possibly. The World Health Organization said there was no scientific evidence Of a delay Of more than six weeks in the administration Of the second dose Of the Pfizer / BioNTech vaccine, but Canada and Germany are believed To be considering this, and Denmark said it would allow a gap Of six weeks. To allow more people To receive a first injection. However, US health Officials have ruled out this possibility.

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