Attempting herd immunity would kill up to 3 million people 2:53
(CNN) -
After overcoming his covid-19 infection, President Donald Trump said he was immune to the virus.
Now, experts say it is possible to become infected again.
Although it is rare.
So 38 million cases worldwide.
A couple of dozen cases of reinfection reported so far, ”Dr. Soumya Swaminathan, chief scientist at the World Health Organization (WHO), told CNN earlier this week.
Dr. Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said health officials this week are beginning to see "several cases" reported as reinfections.
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"Well-documented cases," he said, "of people who became infected, after a relatively short period, measured from weeks to several months, return, become exposed and become infected again."
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"So you really have to be careful because you are not completely 'immune'," Fauci said.
Documented coronavirus reinfection cases
In August, doctors reported that a 25-year-old Nevada man appeared to be the first documented case of covid-19 reinfection in the United States.
The patient was first diagnosed with covid-19 in April.
And, after getting better and testing negative twice, he tested positive for the virus a little over a month later.
A different team of researchers reported in August that a 33-year-old man living in Hong Kong had had COVID-19 twice this year: in March and August.
And earlier this year, an 89-year-old Dutch woman, who also suffered from a rare white blood cell cancer, died after contracting COVID-19 twice, experts said.
She is the first and only person known to have died after being reinfected.
While reinfection of the virus is possible, there are still questions scientists are trying to answer, including who is most likely to be infected again and how long the antibodies protect people from a reinfection of coronavirus.
Scientists study how long antibodies last
Several recently published reports show that immunity to COVID-19 can last for months.
Researchers at the University of Arizona found that antibodies that protect against infection can last for at least five to seven months after a COVID-19 infection.
Given that the pandemic has been going on for less than a year, it will likely take a while before scientists can get a clear picture of immunity.
'That said, we know that people who were infected with the first SARS coronavirus, which is the virus most similar to SARS-CoV-2, still have immunity 17 years after infection.
If SARS-CoV-2 looks anything like the first, we expect the antibodies to last at least two years, and something much shorter would be unlikely, ”Deepta Bhattacharya, an immunobiologist at the University School of Medicine, previously told CNN. from Arizona.
Other studies, one in Massachusetts and one in Canada, supported the idea of long-lasting immunity.
That suggests "that if a vaccine is designed correctly, it has the potential to induce a long-lasting antibody response that can help protect the vaccinated person against the virus that causes COVID-19," said Jennifer Gommerman, Professor of Immunology at the University of Toronto, in a statement.
What is unclear is how second infections could affect any Covid-19 vaccine.
The Nevada man experienced more critical symptoms during his second infection, while the Hong Kong man had no obvious symptoms during his coronavirus reinfection.
"The implications of reinfections could be relevant for vaccine development and application," according to the authors of a recent study in
The Lancet
.
The severity of the disease could influence the antibodies
There's something else that researchers have started to notice: People who have a tougher fight with the disease tend to have a stronger immune response.
"There is a difference between people who are asymptomatic, who had a very mild infection, there seems to be a slightly higher number of those who have no detectable antibodies," says Soumya Swaminathan of the WHO.
"But almost everyone who has moderate to severe disease has antibodies," he explained.
Bhattacharya from Arizona echoed that finding.
"People who were sampled in the intensive care unit had higher levels of antibodies than people with milder disease," he said.
And he added that he doesn't yet know what that will mean for long-term immunity.
CNN's Maggie Fox contributed to this report.
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