COVID-19: Understanding vaccine immunity and antibodies

The COVID-19 vaccine is designed to keep people out of the hospital and prevent them from becoming seriously ill.

According to the Centers for Disease Control and Prevention (CDC), nearly two-thirds of the United States population have received their initial vaccination against COVID-19. However, there are still periodic increases in the number of COVID-19 infections across the country. 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.

While breakthrough cases weren't as common with the Delta variant, they have become 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, says 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. Booster shots are now an important part of being optimally protected from COVID-19.

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 or Moderna) or one dose of the Johnson & Johnson 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 says.

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 did, 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 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, notes 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 infection, but it's not clear whether you're protected six months on," Dr. Sands says.

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?

With many places loosening restrictions or ending mask mandates, vaccination is just one way to protect yourself against COVID-19.

"It's most important to mask when you are in a small or enclosed space with lots of people," Dr. Sands says. "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.