How Long Is Too Long To Wait Between Doses Of The COVID-19 Vaccine?

by Elaine Roth
Hakan Nural/Unsplash

The theme of 2021 so far seems to be vaccines. It’s the thing everyone is talking about and the reason that many of us are finally feeling a little hope after nearly a year of pandemic living.

But so far the country’s vaccination rollout has been less than what we all hoped it would be. The United States missed its projected 2020 vaccination goal by more than 75%, according to Vox, Only 4.8 million first dose vaccinations were given, which is far short of the projected 20 million doses.

President Biden has an ambitious plan to get 100 million doses out in the first 100 days. (I’m hopeful!) To make that happen, obviously we need to ramp up supply and distribution. Currently there are two vaccines that have been authorized for emergency use in the United States—one from Pfizer/BioNTech and the other from Moderna. Both require two doses, given 21 and 28 days apart, respectively.

One of the ideas that has been floated to get vaccines in arms faster is to distribute all the of the doses that have been held in reserve for a second dose. That’s the idea Britain has employed, and to make it happen has extended the 21-day period between doses to 12 weeks. The CDC has taken a more cautious approach, and issued guidance late last month extending the interval between the first and second dose to up to six weeks after the first dose in cases in which receiving the second dose in the recommend time frame is not possible.

Scary Mommy spoke with Dr. Anthony Harris, M.D., M.B.A., M.P.H, the Chief Innovation Officer and Associate Medical Director for WorkCare, about the recent CDC recommendations regarding wait times between second doses and whether there’s risk involved in delaying your second dose.

How Long Is Too Long For Someone To Wait To Get The Second Dose?

National Cancer Institute/Unsplash

The CDC’s most updated guidance confirms that sticking as close to the guidelines provided by the vaccine manufacturers is best—21 days for Pfizer and 28 days for Moderna—because there are “currently limited data on efficacy of mRNA COVID-19 vaccines administered beyond this window.”

All that being said, the CDC does not recommend restarting the vaccination series if longer than six weeks has gone from the day of the first dose. This would suggest that there is no known harm if the vaccine is delayed beyond the recommended window.

Dr. Harris confirms this idea and notes that there is no “known detriment” to a longer interval between doses. He says, “there’s no hard and fast answer” to this question. The COVID vaccine acts similarly to other vaccines, like hepatitis B, for example, and in terms of the immunity we want to achieve, what matters is the dosing and not the timing.

What Kind Of Protection Does The First Dose Offer?

To answer this question, it’s important to understand what we mean when we say studies show a vaccine is 95% effective against COVID. This percent does not relate to the individual—it does not mean that an individual is 95% protected against the virus, but rather that 95% of people who have been vaccinated will have neutralizing antibodies after their second dose. Five percent of people will not form neutralizing antibodies.

With respect to the vaccines currently on the market, Pfizer and Moderna, Dr. Harris notes that 80% of people will develop neutralizing antibodies after the first dose. They will have the neutralizing antibodies to fight off the virus after the first dose takes effect. The purpose of the second dose is, then, not for the individual, but for the collective—to capture the additional 15% of the population who didn’t respond to the first dose because we want (and need) as many people protected as possible to end this pandemic.

Unlike Pfizer and Moderna, the Johnson & Johnson vaccine that will (hopefully) be available soon is a single dose vaccine with a high efficacy after one dose. 90% of vaccine trial participants produced neutralizing antibodies, according to early reports. As a result, a second dose isn’t needed because most of the population is captured after a single dose.

For those who do form neutralizing antibodies in response to the first dose, there’s no harm in getting the second dose.

In fact, there may be a benefit. In an article for the BBC urging folks who’ve received the first dose of the vaccine to act as if nothing happened, Danny Altmann, professor of immunology at Imperial College London, says, “The reason that people are so keen on boosters and consider them so vital is that they kind of send you into this whole other kind of fine-tuning mode of your immune response.” He explains further that, “once you’ve had your boost you’ll have a higher frequency of memory T cells and ditto to some extent for the size of the pool of memory B cells you’ll have. They’ll also be making higher quality antibodies.”

How Do I Know If I’m Protected From The Virus After One Dose?

John Cameron/Unsplash

Unfortunately, there is no way to know if you are in the 80% that develops neutralizing antibodies after the first dose or the 5% that never develops antibodies even after the second dose. At least not yet.

Dr. Harris and his team at Workcare are trying to develop a Titer test that could measure the levels of COVID-19 antibodies in the blood. “The science exists, but commercial scale is not yet there,” he says, but believes a test or product will be available from either Workcare or another initiative by summer.

The availability of a Titer test for COVID-19 neutralizing antibodies could be a game changer when we talk about truly getting back to normal.

Even with questions about antibody levels remaining, Dr. Harris urges everyone to get the vaccine as soon as it’s available to them, because while vaccines do have some unanswered questions, COVID has proven to be the greater risk. “We do know outcomes and side effects of COVID infection—stroke, heart disease, and other vascular diseases—we know these can happen and risk of this is far greater than any risk we’ve seen in studies.”

The vaccines are coming, and by all accounts they are the light at the end of the dark tunnel that will lead us back to normal. The faster we can get more people vaccinated and protected from COVID, and understand what that protection truly means, the faster we can begin to return to some version of normal.

Information about COVID-19 is rapidly changing, and Scary Mommy is committed to providing the most recent data in our coverage. With news being updated so frequently, some of the information in this story may have changed after publication. For this reason, we are encouraging readers to use online resources from local public health departments, the Centers for Disease Control, and the World Health Organization to remain as informed as possible.