When you’re infected with the coronavirus, your body pumps out special proteins called antibodies that help protect you from getting sick again. They stick around for months or years, slowly diminishing with time.
Now, a new small study shows antibodies lodged in your airways wane more quickly and completely disappear three months after infection compared to those swimming in your blood, which remain stable for at least eight months.
But vaccination can quickly trigger a strong increase in antibody levels, both in the blood and airways, especially after two doses of a two-dose vaccine, including the Pfizer and Moderna shots, according to the study published Oct. 19 in the journal JCI Insight.
Researchers in Sweden found that antibody levels in airways were even higher in people who had recovered from COVID-19 after two doses of a coronavirus vaccine than those acquired from their infection.
People who never had COVID-19 before vaccination “had much lower or undetectable levels” of antibodies in their airways, however, researchers said in a news release.
The findings are important given lungs are the first organ of the body to be affected by COVID-19, according to the American Lung Association.
Early on in your infection, the coronavirus is busy invading cells that line your airways. These cells, called epithelial cells, are responsible for catching and clearing foreign invaders, like pollen and viruses, the group says. Because the coronavirus is attacking your respiratory system’s first line of defense, your airways become flooded with debris and fluids.
A laboratory study on about a million human airway cells infected with the coronavirus found that over four days, the virus grew from about 1,000 particles to about 10 million.
“The dramatic increase in viral particles helps to explain how COVID-19 spreads so easily from the lungs to other parts of the body and — all too often — on to other individuals, especially in crowded, indoor places where people aren’t able to keep their distance,” Dr. Francis Collins, former director of the National Institutes of Health, wrote in a blog post last year.
The new study shows people who already had COVID-19 can still benefit from vaccination. Boosted antibodies in your airways suggest you may benefit from greater protection against reinfection, and may be less likely to spread the virus to others.
It’s unclear what level of antibodies is required for protection against coronavirus infection or severe disease, but studies on other pathogens suggest higher antibody levels equal greater protection. Scientists are still learning whether this is true of COVID-19.
It’s important to note antibody levels don’t reveal everything there is to know about protection against a disease, including COVID-19. There are other components of the immune system that play similar roles to antibodies.
“Our results demonstrate that to only study blood does not reflect the antibody levels in the respiratory tract, which likely play a major part in neutralising the virus locally,” study co-author Karin Loré, a professor of medicine at the Karolinska Institutet in Sweden, said in the news release. “Completing the vaccination with a second dose may therefore be important for achieving optimal immune responses and reducing the spread of infection between individuals.”
The study included 147 people who had COVID-19 between March and May 2020. Researchers monitored them for up to eight months after infection. Twenty participants’ blood and airways were analyzed for antibodies after vaccination with the Pfizer, Moderna or AstraZeneca vaccines, the latter of which is not authorized for use in the U.S.
People who did not previously have COVID-19 before vaccination were included in the study as a control group.
The team also found that people who had more severe COVID-19 developed more antibodies upon recovery than those who had a mild case. And in people who already had COVID-19, a second dose of a vaccine “did not have such a strong effect on the antibody levels in the blood.”
“This is in line with earlier studies on the antibody response in the blood where people who previously had COVID-19 showed a strong increase in antibodies after the first vaccine dose, but only a small increase – if any – after the second,” the researchers said.