Have you been vaccinated and want to know if you are protected?

Now that tens of millions of Americans are vaccinated against the coronavirus, many are asking: Do I have enough antibodies to be protected?

For the vast majority of people, the answer is yes. That hasn’t stopped hordes from flocking to labs for antibody tests. But To obtain a reliable response to the test, people who have been vaccinated must undergo a specific type of test at the right time.

If you get tested too early or choose one that detects the wrong antibodies – which is very easy to do, given the bewildering range of tests available today – you may believe that you are still vulnerable when This is not the case.

In reality, scientists would prefer that the average vaccinated person not undergo any antibody test, considering that this is not necessary. In clinical trials, vaccines licensed in the United States elicited a strong antibody response in virtually all participants.

“Most people shouldn’t be worried about this,” said Akiko Iwasaki, immunologist at Yale University.

But antibody tests can be crucial for people with weakened immune systems or who take certain medications, a broad category that encompasses millions of people who receive organ donations, who have certain blood cancers, or who have certain blood cancers. are taking steroids or other drugs that suppress the immune system. system. A growing body of evidence suggests that a significant proportion of these people do not produce a sufficient immune response after vaccination.

If you have to take the test, or if you just want to take it, it’s essential that you take the right kind of test, said Iwasaki: If you really understand what the test does, people might get the wrong feeling that They did not do it. developed antibodies. “

At the start of the pandemic, many commercial tests were designed to look for antibodies against a protein in the coronavirus called nucleocapsid, or simply N, because after infection these antibodies were abundant in the blood.

But these antibodies aren’t as strong as those needed to prevent viral infection, and they don’t last as long either. More importantly, antibodies to the N protein are not produced by vaccines licensed in the United States; Instead, these vaccines produce antibodies against another protein on the surface of the virus called a spike.

If people who have never been infected are vaccinated and then tested for antibodies to the N protein instead of the spikelet, they can be badly affected.

David Lat, a 46-year-old legal writer from Manhattan, was hospitalized with COVID-19 for three weeks in March 2020, chronicling most of his illness and recovery on Twitter.

Over the next year, Lat was tested for antibodies on several occasions, for example, while visiting his pulmonologist or cardiologist for follow-up or to donate plasma. His antibody levels were high in June 2020, but declined steadily over the following months.

The descent “didn’t bother me,” Lat recalled recently. “I had been told to expect them to decrease naturally, but I was happy to stay positive.”

Lat was fully vaccinated on March 22 of this year. But an antibody test carried out on April 21, ordered by his cardiologist, barely came back positive. Lat was stunned: “I would have thought that a month after being vaccinated, my antibodies would skyrocket.”

Lat took to Twitter for an explanation. Florian Krammer, an immunologist at Icahn Mount Sinai School of Medicine in New York City, responded by asking which test had been used. “That’s when I looked at the fine print of the test,” Lat said. He realized it was an antibody test against the N protein, not the spikelet.

“It seems that by default they just do the core exam,” Lat said. “It never occurred to me to ask for a different test.

In May, the Food and Drug Administration advised against the use of antibody tests to assess immunity – a move that has drawn criticism from some scientists – and provided only cursory information about the tests to providers of the drug. health care. Many doctors still ignore the differences between antibody tests, or the fact that the tests only measure one form of immunity to the virus.

The rapid tests that are generally available give a positive or negative result and may lack low levels of antibodies. One type of lab test, called an Elisa test, can provide a semi-quantitative estimate of antibodies against the spike protein.

It is also important to wait to be tested at least two weeks after the second injection of Pfizer-BioNTech or Moderna vaccines, when antibody levels have risen enough to be detectable. For some people who receive the Johnson & Johnson vaccine, this period can be up to four weeks.

“The timing, the antigen and the sensitivity of the test are very important,” Iwasaki said.

In November, the World Health Organization has set standards for antibody testing, which makes it possible to compare the different tests. “Now there is a lot of good evidence,” Krammer said. “Little by little, all these builders, all these places that manufacture them are adapting to international units.”

Antibodies are only one aspect of immunitySaid Dorry Segev, transplant surgeon and researcher at Johns Hopkins University: “There’s a lot going on below the surface that antibody tests don’t directly measure.” The body also maintains what’s called cellular immunity, a complex network of defenses that also respond to invaders..

Still, for someone who has been vaccinated but immunocompromised, it can be very helpful to know that protection against the virus is not what it should be, he said. For example, a transplant patient with low antibody levels could use the test results to convince an employer to continue to telecommute.

Lat did not request another review. Just knowing that the vaccine most likely gave him another surge of antibodies, despite his test results, reassured him enough: “Hope the vaccines work.”

(c) The New York Times

Apoorva Mandavilli is a reporter for The Times and focuses on science and global health. In 2019, he won the Victor Cohn Award for Excellence in Medical Science Reporting. @apoorva_nyc

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