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People who contract Covid-19 may develop natural immunity to the coronavirus, but they should still get vaccinated, according to researchers and federal and state guidance.

That’s because studies show getting vaccinated strengthens natural immunity against the virus, and that immunity can wane as quickly as three months from an initial infection.

Some people may prefer to wait to get infected and build up antibodies that way. But doing so comes with the risk of hospitalization and death that could be avoided with vaccination.

The issue has emerged as a point of contention in government efforts to get as many people vaccinated as possible to slow the spread of the respiratory virus while vaccine opponents point to evidence, including a recent study using data from Israel, that suggests natural immunity may be more effective in preventing reinfection.

“You shouldn’t wait around for natural immunity from a real infection thinking you’ll have better immunity, because that can kill you,” said Robert “Chip” Schooley, a virologist and infection disease specialist at the University of California at San Diego.

More than 63% of Hawaii’s population has been fully vaccinated against Covid, and more than 71% has had at least one shot. That’s a relatively high rate compared to other states, but the delta variant has continued to rage among Hawaii’s unvaccinated residents nonetheless.

The state reported 13 coronavirus deaths and 455 new cases on Wednesday, although the Department of Health said the number of infections was a partial count due to an electronic lab reporting delay earlier this week.

Also concerning is that 438 Covid patients were hospitalized, and state officials have said that some 90% of them were unvaccinated. Some hospitals are operating over capacity as they grapple with both Covid and non-Covid cases.

In Hawaii, state officials have said 90% of Covid hospitalizations are among unvaccinated people, even though they make up less than 40% of the state’s population.

State, federal and local governments have been pushing for more people to get vaccinated but some people have resisted for a variety of reasons. One argument is that the vaccine is unnecessary if they’ve already gotten sick and built natural immunity.

But the Centers for Disease Control and Prevention recommends that people who get sick with Covid get vaccinated against the virus because it’s unclear how long immunity from infection lasts and vaccines can help prevent reinfection.

“Evidence is emerging that people get better protection by being fully vaccinated compared with having had COVID-19,” . “One study showed that unvaccinated people who already had COVID-19 are more than 2 times as likely than fully vaccinated people to get COVID-19 again.”

Patients may need to wait 90 days post-infection to get vaccinated depending on what treatment they underwent, the agency said.

What We Know About Covid Immunity

The science around the coronavirus is constantly evolving, but it’s clear that immunity from catching Covid can vary widely from person to person.

“The rationale of vaccinating infected people is to really provide them with the best opportunity to have a long-lasting effective protective immune response to the virus,” says Sandra Chang, a University of Hawaii professor who specializes in infectious disease immunology and vaccine development.

Natural immunity, Schooley said, can range from three months to years depending on the person. On average, people who have mild infections are likely to develop less immunity than people who get so sick from Covid that they have to be hospitalized, he said.

Schooley said on average, slightly better immunity can be developed when you have a natural Covid infection than with a vaccine, but there’s no guarantee how long it will last and the risk of hospitalization and death is higher.

“What that means is you take 100,000 people and they get infected with Covid, some of them will die, some of them will get into the hospital on a respirator, some will have long-term disabilities, some will have severe enough disease to miss work for a week or two, and some will have mild disease, and on average, they’ll be less likely to get infected again in six months than 100,000 who got vaccinated,” he said. 

“But those 100,000 people who get vaccinated will not be at risk of dying … or be in the hospital or missing two weeks of work because they were so sick,” he said.

Unvaccinated people are 30 times more likely to be hospitalized than vaccinated people, he said.

What About That Israel Study?

A  found immunity to the delta variant was stronger among people who got infected with Covid compared with people who were only vaccinated against coronavirus.

The study has been widely reported since it was released as a preprint on Aug. 25. Preprints are studies that have not yet been peer reviewed.

“It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice,” a note at the top of the study says, emphasizing the word “not” with italics.

Yet the study has been broadly circulated in the media and social media, in part because it’s the largest study yet on the issue. Its findings include that people who previously caught Covid were less likely to get hospitalized the second time around than someone who caught Covid for the first time after being vaccinated.

The study also found that people who got infected with Covid and subsequently received at least one vaccine dose were better protected against the delta variant than people who were only infected and never vaccinated.

Schooley said analyzing reinfection can be challenging depending on the patient population. Younger populations that have mild Covid infections may get less initial immunity from a vaccine, whereas older populations that have worse Covid illnesses might be more protected after a tough bout with the illness.

Regardless, he thinks the Israel study complements other studies that show the importance of the vaccine. He noted that the study found zero deaths, including among people who caught the virus after getting vaccinated.

Chang from the University of Hawaii pointed to additional peer-reviewed studies that were recently published that underscore the importance of vaccinations even among people who were previously sick. She described that found that even after patients catch Covid, “some individuals, especially young people, don’t develop a detectable immune response.”

“This indicates that these individuals need to be vaccinated to be protected against infection,” she said.

found that getting one Pfizer-BioNTech or Moderna shot would strengthen immunity against Covid for previously infected patients.

Risk Of Death And Hospitalization

Chang said one of the problems with relying on natural immunity versus the vaccine to get Covid protection is that it risks severe illness and death.

That’s not a good idea in Hawaii where hospitals are overflowing, and Covid patients are forcing hospitals to delay other surgeries — including one woman’s breast cancer surgery — because there aren’t enough beds with staff for everyone.

“Why take a chance of yourself getting infected and possibly getting very ill in response to infection when you can achieve an immune response by getting a vaccine which is safe?” asked Chang, who is also a member of the medical advisory group to the state Department of Health.

“Getting vaccinated not only protects yourself but protects those you love and protects the community,” she said.

Schooley said he’s concerned that politicians might misinterpret the Israel study as a reason to encourage people not to get vaccinated.

“The problem with that advice is people die getting the disease. They don’t die getting the vaccination,” he said. “Studies like this get twisted by people who want to convince people not to get vaccinated.”

He emphasized that the study from Israel doesn’t recommend against vaccinations, and in fact says that immunization shots boost natural immunity.

“If you get a natural infection you get a good chance of dying and getting hospitalized and that doesn’t happen with a vaccine,” he said. “So the best scenario is to get vaccinated.”