Does delaying the 2nd dose allow it to inactivate?


The decision taken by the UK government at the end of last year to allow a delay of up to 12 weeks between doses of the two vaccines authorized in the country has divided the opinion of infectologists and provoked heated debates among experts.

Concerned about the alarming increase in cases and terrified by the spread of a new highly contagious strain of coronavirus, the UK health authorities wanted to increase, even with a half dose, the protection of a greater number of people.

The British were not alone with the idea. Last Monday (11), the Russian government revealed a clinical trial in which the application of the two-dose Sputnik V vaccine in a single dose, with the name Sputnik Light, is being tested as a “temporary” solution to assist countries with high infection rates.

On Tuesday (12) it was the United States’ turn to adhere to the half-dose strategy with the announcement that the country would no longer retain 50% of the vaccine supply to ensure the delivery of the second dose in a timely manner.

What do virologists say?

The reaction of healthcare professionals began the day after the UK decision. British-American virologist Paul Bieniasz, of Rockefeller University in New York, tweeted: “I developed a remarkable two-dose vaccine, administered it to millions of people, but was late on the second dose …” He then made a sarcastic warning, arguing that letting a person’s immunity diminish for a while could allow him to reach an ideal point to “create a virus that is capable of neutralizing the vaccine”.

What Bieniasz and several of his fellow virologists fear is that extending the interval between the two doses to vaccinate more people can result in a multitude of half-vaccines over a considerable period, a time when the virus can take advantage to develop mutations resistant to vaccine.

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Experts have not yet reached a consensus on the exact size of the risk of a long delay between the two doses. Microbiologist Andrew Read of Pennsylvania State University warns in Science Magazine that “it’s a carnage out there,” which suggests that “twice as many people with partial immunity have to be better than full immunity for half of them “.


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