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British medical directors – faced with the increased threat of the most transmissible variant and a pressured health service – now recommend that the gap between the first and second dose of vaccine be lengthened to allow more people to receive the first dose and therefore a certain level of protection. He says a second dose of the vaccine can be given within 12 weeks.
The United States, on the other hand, said it would not make any changes to the 21-day interval between doses. Denmark allows up to six weeks between doses.
The WHO Strategic Advisory Group of Experts on Immunization (SAGE) sets the maximum interval between doses at six weeks, as clinical data is available for up to 42 days between doses.
Delay of 2nd dose acceptable “ for a few weeks ”
The committee notes the difficulties countries may face in deploying limited doses of vaccine and their eagerness to immunize as many people as possible in the face of an increasing number of cases.
“SAGE recommends the administration of two doses of this [Pfizer/BioNTech] vaccine within 21 to 28 days ”,SAGE President Dr Alejandro Cravioto said at a press briefing this week.
“While we recognize the lack of safety and efficacy data after a dose beyond the three / four weeks studied in clinical trials, SAGE has arranged for countries in exceptional circumstances to vaccine supply constraints and epidemiological context delay the administration of the second dose for a few weeks in order to maximize the number of people benefiting from a first dose. “
While it recommends that the maximum time between doses be six weeks, the SAGE committee also says that a person who was late to receive the second dose – for whatever reason – can still receive a second dose: “There is no outer limit where we say ‘you cannot get your second dose’.”
Responding specifically to the UK dose spacing strategy, Dr Kate O’Brien, Director, Immunization, Vaccines and Biologics at WHO, said each country weighs the risks and benefits of the strategy against the backdrop of his own situation.
The UK’s chief medical officers say the second dose of authorized COVID-19 vaccines – whether Pfizer / BioNTech or AstraZeneca – should be given within 12 weeks. This is less of a problem with the AstraZeneca vaccine – clinical trials have looked at longer times between doses (albeit in a relatively small group) – but the majority of participants in the Pfizer / BioNTech trials received the second dose after a period of time. defined for 21 days (a small number of participants received the second dose up to 42 days later).
“I think everyone realizes that we operate in a space where the amount of evidence to guide policy decisions is evidence that evolves. What many communities are doing is weighing the evidence we have on efficacy and immunogenicity [been] derived from clinical trials where the schedule of doses is administered within a specified schedule, with respect to what to do around the possibility and some evidence that shows the possibility that the effectiveness of a single dose between the time of the first and second dose is quite high. “
Countries with limited supply need to think about how they distribute the first doses of vaccine in the context of how the supply unfolds; weigh a wider deployment of a first dose versus a second dose delay; and if they want to take the risk of administering the vaccine outside the parameters of clinical trials without proof of efficacy;
“What we are seeing in the world is that different committees assess these risks and discuss these risks in different ways.”
WHO recommendations for pregnant women and people who have had COVID-19
The SAGE committee met on Tuesday (January 5) to review the Pfizer / BioNTech vaccine. Along with the issue of delay between doses, he also made the following recommendations regarding the administration of the vaccine to pregnant women, people who have already had COVID-19, and future research priorities.
Pregnant women: “Due to data limitations, SAGE was unable to provide a recommendation for the use of the vaccine during pregnancy until more safety data became available. However, we have made arrangements for situations in which the benefit of immunizing a pregnant woman outweighs the potential risks, such as health workers at high risk of exposure. We have already done this for other vaccines, such as the use of Ebola vaccine in the Democratic Republic of Congo before.
People who have had COVID-19 in the past: “SAGE recommends that the COVID vaccination be offered regardless of a person’s history of asymptomatic or symptomatic SARS-Co2 infection. Available data currently indicate that symptomatic reinfection within six months of initial infection is rare. Thus, in the context of a limited vaccine supply, people with a PCR-documented SARS-CoV2 infection in the previous six months may choose to delay vaccination until the end of this period.
“This would encourage the use of vaccines for others who have not been exposed to the virus and thus protect a much larger portion of the population.”
Future research priorities: The SAGE committee notes the continued collection of data for authorized vaccines as deployments continue. It sets the priority of vaccine research by evaluating the efficacy of vaccines against SARS-CoV transmission, the duration of protection, the efficacy of the vaccine against variants of the virus (especially in light of new variants emerging from South Africa and the UK), and vaccine efficacy and safety. in children under 16.
It also notes the need to prioritize research on immunogenicity and safety and in particular on co-transmission with other vaccines and the interchangeability of vaccines. “This is especially important with the co-administration for the elderly group with an influenza vaccine if possible.“
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