COVID-19: understanding vaccine immunity and antibodies

Woman getting a vaccine. Text: COVID-19: Understanding vaccine immunity and antibodies

As of June 9, 2022, data from the Centers for Disease Control and Prevention (CDC) shows that more than two-thirds of the United States population is now fully vaccinated against COVID-19. However, there are still periodic increases in the number of COVID-19 infections across the country.

Studies show vaccination remains the best protection against the disease, although some people may develop what’s known as a breakthrough infection of COVID-19 after getting vaccinated. Breakthrough cases weren’t as common with the Delta variant, but they became a more regular occurrence with the Omicron variant, raising questions about vaccine immunity and the spread of COVID-19.

How effective is the COVID-19 vaccine?

Designed to prevent people from getting seriously ill and keep them out of the hospital, the COVID-19 vaccine is very effective against the virus, said Dr. Kenneth Sands, chief epidemiologist at HCA Healthcare. Still, the goal of getting vaccinated isn’t to prevent infection altogether — it’s to reduce the severity of the illness if you do get infected.

Antibodies are protein molecules that your immune system produces to help it fight off harmful foreign substances. Vaccines prompt your body to make these antibodies targeted to specific threats. When you are exposed to a virus, such as the coronavirus that causes COVID-19, the antibodies fight it off. Vaccine immunity wanes over time, which is why some vaccinations require booster shots. These booster shots help raise the number of antibodies back up to a level that’s able to fight off an infection.  Recommended for most people, boosters are an important part of protecting yourself from getting seriously ill or dying from COVID-19. The CDC provides an online tool to determine when or if you (or your child) can one or more COVID-19 boosters.

Fully vaccinated vs. up to date

Currently, the CDC uses the term “fully vaccinated” to describe when you’ve received all recommended doses of the COVID-19 vaccine as part of the initial primary series. This would mean two doses of an mRNA vaccine (Pfizer-BioNTech or Moderna) or one dose of the Johnson & Johnson Janssen vaccine.

“Up to date” means a person has received all of the recommended doses in their primary series, plus any recommended booster doses for which the individual is eligible. “The CDC is using the term ‘up to date’ in anticipation that there may be additional booster doses,” Dr. Sands said.

COVID-19 variants and the vaccine

It’s even more important to get a booster dose to protect against variants such as Omicron, says Dr. Sands. “If you are up to date with COVID vaccination, meaning you have received the initial vaccine series as well as the recommended boosters, the likelihood that you’ll get sick with COVID is about three times reduced,” Dr. Sands says. “The likelihood that you’ll end up in the hospital is about five times reduced.” This is especially true for people who are at a higher risk of becoming very sick from the disease, such as the elderly.

Although the Omicron variant travels through the air in much the same way as the Delta variant, it appears to cause infection more frequently, Dr. Sands says. Despite being more infectious, Omicron does not appear to make people as sick as the Delta variant, and there have been fewer hospitalizations.

What are the most current vaccine recommendations?

The CDC recommends everyone ages 5 and older get their primary series of vaccines. This includes two doses of the Pfizer-BioNTech or Moderna vaccines or one dose of Johnson & Johnson’s Janssen vaccine.

People ages 5 and up who received the Pfizer or Moderna vaccine should also receive a booster shot at least five months after getting the primary series. However, only the Pfizer vaccine is approved by the U.S. Food & Drug Administration (FDA) for those ages 5 to 11. People 18 and older who received the Johnson & Johnson vaccine should get a booster of either the Pfizer or Moderna vaccine at least two months after their first dose.

For those who are over 50, or older than 12 with an immunocompromising illness, a second booster is recommended after at least four months from the first booster.

As more data becomes available about the vaccines, it’s important to note that there have been minimal long-term complications reported so far.

Can you get COVID-19 more than once?

Although your chances of getting COVID-19 decrease if you’ve already had it, you won’t have complete immunity against the disease. There have been cases of people catching COVID-19 two or three times, noted Dr. Sands. Subsequent cases are usually less severe than the first, however. If you’re fully vaccinated and have already had COVID-19, you already have antibodies, meaning that you may have a little more protection against getting it again.

“You may be protected for the period of time from that initial COVID-19 infection, but it’s not clear whether you’re protected six months on,” Dr. Sands said.

Your odds of getting COVID-19 also depend on its presence in the community. The more people who are infected, the more likely they are to infect others in greater numbers. You can help prevent the spread by getting vaccinated yourself and helping as many people access vaccinations as possible.

What additional measures should you take to prevent infection?

The CDC introduced a new tool to help determine what prevention measures are needed to protect yourself and your loved ones, as well as decrease strain on hospitals and health systems. Levels can be low, medium, or high and are determined by looking at hospital beds being used, hospital admissions and the total number of new COVID-19 cases in an area.

Precautions that the CDC promotes to protect yourself and others, based on COVID-19 community levels include:

Low COVID-19 Community Level:

Medium COVID-19 Community Level:

High COVID-19 Community Level:

Check your community’s level and learn more at

Woman and teenage daughter wearing protective masks as they stand in line at airport check-in counter.
Wearing a well-fitting mask or respirator is most beneficial in crowded or poorly ventilated location. At this time, for people aged 2 years or older—including passengers and workers— the CDC recommends properly wearing a well-fitting mask or respirator over the nose and mouth in indoor areas of public transportation and transportation hubs.

“It’s most important to mask when you are in a small or enclosed space with lots of people,” Dr. Sands adds. “But I think you are going to see people making individual decisions — whether they want to protect themselves.”

Some masks are better than others. For example, medical grade (surgical) face masks are multi-ply and offer better protection than a standard cloth face mask. Respirators, which typically carry a designation of “N95” or “KN95,” are designed to offer a better fit and greater filtration, and thus even better protection from airborne particles.

In addition to wearing a mask, you may decide to continue practicing social distancing. You should also continue to wash your hands properly. Talk to your doctor if you have any symptoms of COVID-19 or if you have questions about the vaccine.

Related article: Physicians across HCA Healthcare reflect on key moments in the pandemic’s timeline

About HCA Healthcare

HCA Healthcare, one of the nation's leading providers of healthcare services, is comprised of 182 hospitals and more than 2,300 sites of care, in 20 states and the United Kingdom. Our more than 283,000 colleagues are connected by a single purpose — to give patients healthier tomorrows.

As an enterprise, we recognize the significant responsibility we have as a leading healthcare provider within each of the communities we serve, as well as the opportunity we have to improve the lives of the patients for whom we are entrusted to care. Through the compassion, knowledge and skill of our caregivers, and our ability to leverage our scale and innovative capabilities, HCA Healthcare is in a unique position to play a leading role in the transformation of care.

Recent articles