Immunity against COVID-19 Will Take Weeks after Vaccination, Experts Say

Person with mask vaccinating someone else.

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Key Takeaways

  • Pfizer and BioNTech’s vaccine offers immunity at least seven days after the second dose, and Moderna's vaccine offers immunity at least 14 days after the second dose.
  • Johnson & Johnson's vaccine offers immunity at least 28 days after a single dose.
  • Although immunity is offered through the vaccines, building immunity against COVID-19 takes time and will still require social distancing and mask-wearing.
  • While experts think it may last years, immunity duration is unknown. Therefore, more studies will need to be conducted. 

On December 11, the Food and Drug Administration issued an emergency use authorization (EUA) for a COVID-19 vaccine from Pfizer and BioNTech. Just one week later, the FDA issued an EUA for a COVID-19 vaccine from Moderna. On February 27, the FDA issued a third EUA for a COVID-19 vaccine from Johnson & Johnson. Now authorized for usage, these vaccines will offer immunity to millions of people.

In its Phase 3 clinical trial, Pfizer found a 95% efficacy rate for its COVD-19 vaccine. For Moderna, the efficacy rate was 94.1%. Johnson & Johnson found that its single-dose vaccine was 66% percent effective at preventing moderate to severe disease from COVID-19 and 85% effective at preventing severe disease. But despite these companies' impressive results, medical experts tell Verywell that immunity to COVID-19 will take time, even after vaccination.

According to William Lang, MD, MHA, chief medical officer at the telemedicine company WorldClinic, the body doesn't have immunity immediately after the vaccine has been received. “It takes the body time to make adequate antibodies for any vaccine,” Lang tells Verywell.

What This Means For You

You can consult your primary care provider about the vaccines' effects and how they impact you. Even after being vaccinated, it's important to continue practicing COVID-19 safety precautions for some time, like social distancing and mask-wearing.

How Does Vaccine Dosage Impact Immunity?

Effectiveness in Johnson & Johnson's Phase 3 trial was reached at least 28 days after vaccination with its single-dose shot.

Sometimes, one shot is not enough. Both the Pfizer and Moderna vaccines include a two-shot regimen. Pfizer's second dose is given 21 days after the first, while Moderna's second dose is given 28 days after the initial shot. For the Pfizer vaccine, the effectiveness hasn't been demonstrated until at least seven days after the second dose. For the Moderna vaccine, immunity may not be achieved until at least 14 days after the second dose.

To rev up your body’s immune system, two doses are often required. “The first time primes your body [to the virus]," Lang says. "The second time tells the body that we’re serious about this and you really need to make immunity to it."

Two doses or more are very common when it comes to vaccines. For example, the human papillomavirus (HPV) vaccine requires two doses for children under 15 and three doses for 15 to 26 years and immunocompromised people and hepatitis A and hepatitis B require between two and four doses.

Wearing a Mask after Vaccination

According to William Moss, MD, MPH, executive director of the International Vaccine Access Center at John Hopkins in Baltimore, Maryland, it's crucial that people continue wearing masks even after getting their shots.

Even after vaccination, a large percentage of the population may not be protected because the vaccine isn't 100% effective against COVID-19. “If 95% efficacy holds up, 5% of people who get the vaccine will not be protected after receiving vaccination,” Moss tells Verywell. “That sounds like a small percentage, but when you’re vaccinating millions of people, that’s a large number of people.” 

Johnson & Johnson released data to the FDA that suggests the vaccine may prevent most asymptomatic infections and significantly reduces the risk of transmitting the virus. The Pfizer-BioNTech vaccine may offer a similar benefit, according to a study preprint. However, the transmission data is preliminary and more research is still needed.

Concern remains regarding whether enough people will be willing to get vaccinated in order to mitigate the spread. Herd immunity, which occurs when a large portion of a community develops immunity to a contagious disease, would only protect people when a sufficient percentage of the population is vaccinated. Anthony Fauci, MD, the director of the National Institute of Allergy and Infectious Disease anticipates that the country can return to pre-pandemic life by the end of 2021 only if 70 to 90% of the U.S. population gets vaccinated. 

Catching COVID-19 After the First Dose

Pfizer reported that after the first dose, the vaccine yielded 50% efficacy, with roughly three weeks in between the first and second dose. Moss explains that there is a likelihood that anyone can become infected with COVID-19 within that time period. However, it will depend on whether people continue to follow COVID-19 safety guidelines within the immunity window. 

“How likely they are to contract COVID-19 between the two doses is a function of how intense the transmission is in that particular area,” Moss says. “The likelihood of anyone acquiring infection and COVID-19 within a three week period—that’s not uncommon because the pandemic is out of control.” 

Next Steps

With vaccinations authorized and distribution underway, Moss foresees life returning to pre-pandemic times in phased stages. “As more people get vaccinated, particularly the most vulnerable, I see smaller groups, family gatherings, opening up restaurants, and then, maybe later on, we’ll think about large concert halls or sports stadiums,” Moss says. “Hopefully, mid to third quarter of 2021, we can start moving back to a more normal lifestyle.” 

While immunity status remains unknown, further clinical trials and observational studies need to be conducted in order to evaluate the long-term immunity of the Pfizer, Moderna, and Johnson & Johnson COVID-19 vaccines. “I assume it’s going to last several years, but we don’t know yet how long protection will last," Moss says. In addition, more research is needed on how the vaccines impact different populations, including older adults.

“We’re in the midst of a terrible pandemic. Anything we can do as individuals and as a community to get us through these very hard times is going to benefit us all,” Moss says. “It’s going to decrease the burden on the healthcare system, help us get our economy back, and open up businesses that are so crucial to our society.”

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7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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