Doctors: Even if you've had COVID-19, the virus doesn't grant total immunity
For those who have contracted COVID-19, there's always a risk of reinfection, especially among the unvaccinated, said Bruce Farber, chief public health and epidemiology officer at Northwell Health. Credit: Charles Eckert
Recovering from a bout of COVID-19 doesn’t provide enough long-term natural immunity to ward off future infections without the help of a vaccine, health experts warn.
Infectious disease experts said people who have recovered from COVID-19 likely have about 90 days of immunity, but only from the initial strain they contracted.
"If you were infected a year ago with what's called the ancestral strain, then your chance of getting reinfected is much greater now with the delta strain," said Dr. Bruce Farber, chief public health and epidemiology officer at Northwell Health and chief of infectious disease at North Shore University Hospital and Long Island Jewish Medical Center.
People who recovered from COVID-19 and were not subsequently vaccinated are more than two times more likely to be reinfected than those who were inoculated, according to a study recently released by the U.S. Centers for Disease Control and Prevention.
The new information comes with pressure mounting to boost the numbers of people vaccinated against COVID-19, as the highly contagious delta variant has led to a surge in cases throughout the country.
More than 80% of new COVID-19 cases in the U.S. were because of the delta variant as of July 31, according to the CDC. The agency said delta causes more infections and spreads faster.
The CDC said about 61.3% of U.S. residents 18 and older have been fully vaccinated against COVID-19.
Those who have recovered from the disease and decide against getting the vaccine should not rely on any natural immunity they might have, said Dr. Bruce Polsky, an infectious disease specialist who is chairman of medicine at NYU Langone Hospital-Long Island in Mineola.
"The amount of natural immunity is highly variable from person to person," Polsky said. "You can measure the amount of antibodies, but that doesn’t correlate with the amount of protection you are going to get … it is strongly recommended even if you have had COVID that you get the vaccine."
There always a risk of reinfection, especially among unvaccinated COVID-19 patients, Farber said.
"You can get the infection over and over again even though you have had it before, and that’s not uncommon with a lot of diseases," Farber said. "There are a few where that is not the case, like chickenpox and measles, but those are exceptions to the rule."
Health officials also warned people should not believe they are protected simply because tests show the presence of antibodies in their system.
"It doesn’t show what strain they're going to protect you against," Polsky said. "They just show the amount of a type of antibody against the virus generically, but they don't tell you anything about neutralization."
Farber said immunity to COVID-19 is anything but simple.
"It’s not just antibodies, it’s T-cells and other factors," he said. "The tests that are being done commercially are not really measuring neutralizing antibodies … your immunity is even better if you’ve had COVID and you get the vaccine."
Even people who are fully vaccinated against COVID-19 are not 100% immune to being infected, but they are less likely to fall seriously ill or be hospitalized, infectious disease experts said.
Both Polsky and Farber pointed to the CDC study of Kentucky residents who were infected with SARS-CoV-2, the virus that causes COVID-19, in 2020 and then reinfected in May and June of this year.
The case-controlled study showed people who were not vaccinated were 2.34 times more likely of being reinfected than those who were vaccinated.
The study also noted that "the scientific understanding of natural infection-derived immunity is still emerging" and that new variants might "affect the duration of infection-acquired immunity."
Farber said people who are unvaccinated and get COVID-19 should be vaccinated as soon as they recover, noting an increase in cases and hospitalizations in areas throughout the U.S. with low vaccination rates.
"It’s hard for me to understand the incredible hesitancy that we are seeing," he said. "As a result, look what’s going on."
What to know
People who have COVID-19 can have a natural immunity to the disease lasting about 90 days.
That immunity may only protect them from the particular variant of COVID-19 they had contracted.
Infectious disease experts say unvaccinated people who had COVID-19 and recovered should get vaccinated against the disease.
Lisa joined Newsday as a staff writer in 2019. She previously worked at amNewYork, the New York Daily News and the Asbury Park Press covering politics, government and general assignment.
