Now that hundreds of millions of Americans have been vaccinated against the coronavirus, many are wondering: Do I have enough antibodies to keep me safe?
For most people, the answer is yes. That hasn’t stopped the crowd from stamping out the local doctor-in-the-box for antibody testing. But in order to get a reliable answer from the test, vaccinated people have to get a specific type of test, and at the right time.
do the test too early, or rely on one that looks for the wrong antibodies – it’s all too easy to do, given confusing array of tests Available now – and you can still consider yourself vulnerable when you’re not.
Indeed, scientists would prefer that the average vaccinated person not get the antibody test at all, on the grounds that it is unnecessary. In clinical trials, vaccines authorized in the United States provoked a strong antibody response in nearly all participants.
“Most people don’t have to worry about this,” said Akiko Iwasaki, an immunologist at Yale University.
But antibody tests may be important for people who have weak immune system or those who take certain medications – a broad category that includes millions of people who are recipients of organ donations, have certain blood cancers, or who take steroids or other drugs that suppress the immune system. Mounting evidence suggests that a significant proportion of these people do not produce an adequate antibody response after vaccination.
It’s essential to get the right kind of test if you want to, or just want to, get tested, Dr. Iwasaki said: “I’m a little hesitant to recommend testing to everyone, because unless they’re actually doing it. By understanding what the test is doing, people may misunderstand that they have not developed any antibodies.”
At the start of the pandemic, several commercial tests were designed to look for antibodies to a coronavirus protein called the nucleocapsid, or just N, because after infection, those antibodies were plentiful in blood.
But these antibodies are not as powerful as those needed to prevent virus infection, nor do they last long. More important, antibodies to the N protein are not produced by authorized vaccines in the United States; Instead, those vaccines stimulate antibodies to another protein sitting on the surface of the virus, called a spike.
If people who had never been infected are vaccinated and then tested for antibodies to the N protein instead of the spike, they could be in for a severe shock.
David Lato, a 46-year-old legal writer in Manhattan, was hospitalized for COVID-19 for three weeks in March 2020, and took to Twitter to share most of his illness and recovery.
The following year, Mr Lett was tested several times for antibodies – when he went to his pulmonologist or cardiologist for follow-up, for example, or to donate plasma. His antibody levels were high in June 2020, but fell steadily in the following months.
The fall “didn’t worry me,” Mr. Latt recently recalled. “I was told to expect they would subside naturally, but I was just glad I was still positive.”
Mr Lett was fully vaccinated by 22 March this year. But an antibody test ordered by his cardiologist on April 21 was barely positive. Mr Latt was stunned: “I would have thought that a month after vaccination, I would have antibodies through the roof.”
Mr. Lati turned to twitter for an explanation. Florian Kramer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York, responded, asking Mr. Latt which test was used. “That’s when I saw the fine print on the test,” said Mr. Latt. They realized that this was a test for antibodies to the N protein, not spike.
“It seems that by default, they only give you the nucleocapsid,” said Mr. Latt. “I never thought to ask differently.”
In May, the Food and Drug Administration recommended against the use of antibody tests to assess immunity — a decision that included drawn criticism Some provided only bare-bones information about the test, from scientists — and health care providers. Many doctors are still unaware of the difference between antibody tests or the fact that the tests measure just one form of immunity to the virus.
Commonly available rapid tests give a yes-no result and may miss low levels of antibodies. A certain type of laboratory test, called an ELISA test, can provide a semi-quantitative estimate of antibodies to the spike protein.
It is also important to wait for testing at least two weeks after the second shot of Pfizer-BioNTech or Moderna Vaccines, when antibody levels will be high enough to be detectable. For some people receiving the Johnson & Johnson vaccine, this period can be up to four weeks.
“It’s the timing and the antigen and the sensitivity of the assay – these are going to be very important,” Dr. Iwasaki said.
World Health Organization in November set standards For antibody testing, allows comparison of different tests. “There are a lot of good tests out there,” Dr. Kramer said. “Slowly, all these manufacturers, all these places that run them, are adapting to international units.”
Johns Hopkins University transplant surgeon and researcher Dr. Antibodies are just one aspect of immunity, Dori Segev said: “There’s a lot going on beneath the surface that antibody tests aren’t measuring directly.” The body also maintains so-called cellular immunity, a complex network of defenders that also respond to invaders.
Still, for someone who has been vaccinated but lacks immunity, it can be very helpful to know that protection from the virus is not what it should be, he said. For example, a transplant patient with a poor antibody level may be able to use the test results to convince an employer that he should continue to work remotely.
Mr. Lett has not asked for another test. Just learning that the vaccine most likely gave her a new surge of antibodies, regardless of her test results, was reassuring enough: “I believe vaccines work.”