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Dangerous coronavirus strains: a consequence of delaying the second vaccine dose?

With so many variables on the table, the world is still contemplating the consequence of taking the new rolled-out coronavirus vaccines. On one hand, the vaccine presents a safe solution to a problem that has been plaguing our world for a year. On the other, there is so much confusion behind key steps regarding it. One of them is the consequence of delaying the second vaccine dose. 

A risky plan

As a solution for the limited amount of coronavirus vaccines available, some countries are planning to approve a dangerous plan that revolves around holding back the second dose of the vaccine. Basically, for the tested vaccine to work, the patient must take two doses with a certain amount of time left between each one. However, with the slow rollout, only a limited number of people are getting the vaccine. Thus, by delaying when people receive the second vaccine dose, the number of people receiving the currently available doses will double. 

That plan is now taking place in the United Kingdom, where a new coronavirus variant appears to be more contagious than other known ones. Thus, the concerned officials are choosing to extend the time needed between each vaccine dose, from three or four weeks to up to three months. 

On the other hand, the United states scratched the idea of holding back second shots of COVID-19 vaccines after president Joe Biden suggested he will release all the shots. However, the mere consideration of the plan raises the possibility and concern of it happening in case of manufacturing problems. Moreover, Norman Baylor, former director of the U.S. Food and Drug Administration (FDA), called the possibility of the plan“very risky”. “I understand some of the rationale to do this, but again, it’s not really data-driven,” Baylor stated. “It’s a very risky venture because if it fails, you’re in worse shape.”

 Harmful mutations

Since we’re navigating unknown waters, delaying the second dose of the vaccine is a gamble that experts are warning against. According to Ramón Lorenzo-Redondo, a virologist at Northwestern University Feinberg School of Medicine in Chicago, officials “shouldn’t gamble [their] best tools” to fight the pandemic. Then he adds “we don’t want to fuel [potential viral evolution] by doing suboptimal immunization of the population.”

Delaying the second dose will mean millions of people going about their normal day with only partial immunity. Therefore, this could open a window for or harmful mutations of the virus to arise.

Weaker immune response

With complete vaccination, patients will probably become fully immune to the virus. Hence, the immune system will, in theory, spawn large numbers of neutralizing antibodies to stop viruses from getting into cells while immobilizing harmful mutations before they arise. On the other hand, with only partial immunity, the immune system response will be likely weaker. 

Furthermore, only partially fighting the virus may provide it with more time for variants with immune-dodging mutations to arise. Therefore, it might give the virus the chance to thrive and be transmitted to other people. It may also increase the virus’s chances to accumulate vaccine-evading mutations than in the case of lower infection numbers.

Controlling the coronavirus changes

On the other hand, some experts aren’t worried about the delayed doses. In fact, some believe that it will eventually help in the fight against the pandemic. According to Sarah Cobey, an epidemiologist and evolutionary biologist at the University of Chicago, increasing the amount of the vaccinated population with only the first dose will aid in controlling the amount of change the coronavirus undergoes. Even the partial protection from a single vaccine dose “will almost certainly lower the prevalence of infection,” she says. Moreover, fewer infections should probably equal fewer coronavirus variants circulating among people.

However, this fact doesn’t eliminate the possibility of risky viral evolution happening as a result of delaying doses. “I think this is something we need to study and we need to look at for sure,” Lauring, an infectious disease physician and virologist at the University of Michigan Medical School, said. As things stand now, “I’m not sure we know enough that we can really confidently say what one or other [vaccine-dosing] strategy is going to do.” 

In brief, delaying the second dose is a risky gamble. The plan prevailing can aid in the overall fight against the pandemic. However, losing it will leave drastic consequences. 


Jan. 7, A. K. |. (2021, January 7). “Very risky” to delay the second dose of the COVID-19 vaccine, says the former. TheHill., D. (2021, January 14). Experts Debate Wisdom of Delaying Second COVID-19 Vaccine Dose. Medscape., H. (2021, January 15). Could delaying a second vaccine dose lead to more dangerous coronavirus strains? Science News.