Now that tens of millions of Americans have been vaccinated against the coronavirus, many wonder: do I have enough antibodies to protect myself?
For the vast majority of people, the answer is yes. That didn’t stop hordes from trudging to the local Doc-in-a-Box for antibody testing. But in order to get a reliable answer from tests, the vaccinated must take a certain type of test at the right time.
Take the test too early or rely on one to look for the wrong antibodies – all too easy given the confusing array of tests available now – and you may think that if you do, you may still be vulnerable are not.
In fact, scientists would prefer the average vaccinated person not to have any antibody tests at all, as this is unnecessary. In clinical trials, the US-approved vaccines elicited a strong antibody response in virtually all participants.
“Most people shouldn’t worry about that,” said Akiko Iwasaki, an immunologist at Yale University.
However, antibody tests can be crucial for people with weak immune systems or for those taking certain medications – a broad category that encompasses millions of people who are recipients of organ donations, have certain types of blood cancers, or are taking steroids or other drugs, that suppress the immune system. More and more evidence suggests that a significant proportion of these people do not produce an adequate antibody response after vaccination.
If you need or just want to get tested, getting the right type of test is important, said Dr. Iwasaki: “I hesitate to recommend a test to anyone, because if they haven’t really understood what the test does, people could get this false feeling that they have not developed antibodies.”
At the beginning of the pandemic, many commercial tests were developed to look for antibodies to a coronavirus protein called nucleocapsid, or simply N, as these antibodies were abundant in the blood after infection.
However, these antibodies are not as strong as those needed to prevent viral infection and do not last as long. More importantly, antibodies to the N protein are not produced by vaccines approved in the United States; Instead, these vaccines provoke antibodies against another protein that sits 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 spike, they may be in shock.
David Lat, a 46-year-old Manhattan lawyer, was hospitalized for three weeks for Covid-19 in March 2020 and has recorded most of his illness and recovery on Twitter.
In the following year, Mr. Lat was tested several times for antibodies – for example by his pulmonologist or cardiologist in order to carry out follow-up examinations or donate plasma. His antibody levels were high in June 2020 but steadily declined in the months that followed.
June 20, 2021, 1:02 p.m. ET
The decline “didn’t worry me,” Mr. Lat recently recalled. “I was told to expect they would of course wear off, but I was just glad I was still positive.”
Mr. Lat was fully vaccinated on March 22nd this year. But an antibody test ordered by his cardiologist on April 21 was hardly positive. Mr. Lat was stunned: “A month after the vaccination I would have thought I had antibodies through the roof.”
Mr. Lat reached out to Twitter for an explanation. Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York, responded and asked Mr. Lat which test had been used. “That’s when I looked at the fine print of the test,” said Mr. Lat. He realized it was a test for antibodies to the N protein, not the spike.
“It seems they just give you the nucleocapsid by default,” said Mr. Lat. “I never thought I’d ask for another.”
In May, the Food and Drug Administration recommended against the use of antibody tests to assess immunity – a decision criticized by some scientists – and only provided health care providers with bare information about tests. Many doctors are unaware of the differences between antibody tests or the fact that the tests only measure one form of immunity to the virus.
Generally available rapid tests give a yes-no result and can miss low antibody levels. A specific type of laboratory test called the Elisa test can provide a semi-quantitative estimate of the antibodies to the spike protein.
It is also important to wait at least two weeks after the second vaccination of the Pfizer BioNTech or Moderna vaccine before testing if the antibody levels have risen enough to be detectable. For some people receiving the Johnson and Johnson vaccine, this period can be up to four weeks.
“The timing, antigen, and sensitivity of the assay will be very important,” said Dr. Iwasaki.
In November, the World Health Organization (WHO) set standards for antibody tests that allow different tests to be compared. “There are a lot of good tests now,” said Dr. Krammer. “Little by little, all of these manufacturers, all of these places that operate them, are adapting to international units.”
Antibodies are only one aspect of immunity, noted Dr. Dorry Segev, transplant surgeon and researcher at Johns Hopkins University: “A lot happens beneath the surface that antibody tests don’t measure directly.” The body also receives what is known as cellular immunity, a complex network of defenders that also respond to intruders.
Still, it can be very helpful for someone who is vaccinated but immunocompromised to know that protecting against the virus is not what it should be, he said. For example, a transplant patient with low antibody levels might be able to use test results to convince an employer that he or she should continue to work remotely.
Mr. Lat did not request another test. Just to find out that the vaccine, despite its test results, most likely led to a renewed rise in antibodies was reassuring enough: “I trust the vaccines will work.”