Does It Matter If Your Second Dose of the COVID-19 Vaccine Is Delayed?

Experts say you shouldn’t be overly concerned if your second dose of the COVID-19 vaccine is delayed for a few days or even a few weeks. MCKINSEY JORDAN/Stocksy

Experts say you shouldn’t worry too much if your second dose of the …

Experts say you shouldn't be overly concerned if your second dose of the COVID-19 vaccine is delayed for a few days or even a few weeks. MCKINSEY JORDAN/Stocksy
  • Experts say you shouldn’t worry too much if your second dose of the COVID-19 vaccine is postponed for a few days or even a few weeks.
  • Nonetheless, they recommend you make certain your follow-up dose is completed within 6 weeks of the first shot.
  • They say second doses are more important now due to the emergence of COVID-19 variants.
  • They add that the new single-dose Johnson & Johnson vaccine makes things easier.

Supply shortages could mean those waiting for a second dose of the COVID-19 vaccine may have to keep waiting, but experts say there's no need to panic.

Both the Pfizer and Moderna vaccines are given in a two-dose series with a 21-day interval between doses for the Pfizer vaccine and a 28-day interval between doses for the Moderna vaccine.

Experts say those waiting for their second shot shouldn’t worry if it is delayed.

“If your dose is delayed for a few days or a few weeks, I would not be concerned about that,” Dr. Dean Blumberg, chief of pediatric infectious diseases at the University of California Davis, told Healthline.

“Ideally, people would get the vaccine on time, but if it is delayed, you don't have to restart the vaccine series. We do know that one dose of vaccine results in about 90 percent protection in terms of the Pfizer-BioNTech and Moderna vaccines. That begins about 2 weeks following the first immunization,” Blumberg said.

According to data from the Centers for Disease Control and Prevention (CDC), more than 60 million people in the United States have received at least one dose of the COVID-19 vaccine. Of them, more than 31 million have been given two doses.

Dr. Grace Lee, an infectious disease specialist at Stanford University in California, says part of the concern in delays of the second dose is a weakening immune response from only one shot.

“We don’t have any information about the durability of that immune response. If you haven't had an infection with the new coronavirus, the first dose is considered your priming dose. Typically, the boost ensures your immune response would be durable over time. So, if you only get one dose, the concern I would have personally is whether or not there would be waning,” she told Healthline.

Whether it’s more important for more people to have had the first shot or completed the whole series with both shots is complex.

“It’s very complicated. On the one hand, modeling suggests the first dose is more important than the second dose, and that getting that first dose into people will have more of a population impact. Yet, we also know that when we have these priority groups, it’s very important to prioritize those who are most at risk, such as older individuals as well as essential and healthcare workers,” Blumberg said.

“I think there needs to be a combination distribution to make sure those older individuals are fully protected as well as healthcare workers and essential workers,” he added.

Clinical guidelines from the CDC state the Pfizer and Moderna vaccines should be given as close to the recommended interval (21 days for Pfizer and 28 for Moderna) as possible.

If it is not feasible to adhere to the recommended interval and a delay in vaccination is unavoidable, the second dose of Pfizer/BioNTech and Moderna COVID-19 vaccines may be administered up to 6 weeks (42 days) after the first dose,” the CDC states.

Currently, there is limited information on how effective the COVID-19 vaccine is if the second dose is given outside a 6-week window.

“What the CDC has said has been ‘don’t let doses sit on the shelves,’” Lee said. “Meaning don’t hold doses trying to make sure that everyone gets a second dose on day 21 or day 28. Make sure that you’re giving whatever doses you have under the assumption that the supply chain will come in and by the time the individuals are ready to get their second dose, there will be additional supply available. I think this is the right principle.”

The variant effect

Dr. William Schaffner is an infectious diseases expert at Vanderbilt University in Tennessee.

He says the emergence of new strains of the virus means getting both doses is more important than ever.

“The amount you get from the first dose actually is enough to protect you from the standard COVID-19 strain, the parent strain,” Schaffner told Healthline. “However, the variants are a little bit variant from that main dose and by taking the second dose you get much more antibody, which is more protective against the variants. Since the variants have come out, it becomes even more important to get that second dose.”

He says follow-up from clinics to ensure people get their second dose may be variable and some responsibility must lie with the individual.

“We don’t want second doses dropped. There is an adage among the vaccine crowd that says a dose delayed is often a dose never received so it is important on the part of the individual who has been vaccinated and whose dose was delayed to do the follow-up,” Schaffner said.

The Johnson & Johnson factor

The recent approval of the single-shot Johnson and Johnson vaccine has experts hopeful more people will be vaccinated.

“That really simplifies things by having one dose,” said Blumberg. “It simplifies record keeping and the vaccine is easier to transport and to store because it has less stringent cold requirements. This makes it well suited for mobile clinics, pop-up clinics, newly established vaccine administration sites that may not have as much experience, and sites that don’t have as much freezer capacity, such as physician’s offices and more rural areas.”

“This will be good for people who want to be vaccinated quickly, who don’t want to return or can’t return for a second dose, or the mobile population, such as farmworkers who may be seasonal or homeless or homebound people who can’t get out much,” he added.

What you should do

Schaffner says those who have already had their first dose of either the Pfizer or Moderna vaccine should remain vigilant about getting their second dose.

“Get your appointment. Get your second dose. Don’t put it off. Try to get it as close to the designated interval as possible. We want you to be optimally protected and for that, you do need a second dose,” he said.

With three vaccines now offered, Schaffner says for those trying to decide what vaccine is best, the solution is simple.

“The vaccine that is available to you today is the best vaccine,” he said. “Roll up your sleeve and get it.”