Differing opinions on value of antibody titers, third doses
The virus is likely to remain a threat for a year or more to come, and antibody tests may give some indication of who is likely to have the longest-lasting protection, Dr. Safadi said.
“I believe that stronger responders will maintain longer, while the weaker responders will maintain shorter and maybe will need a third shot at some time,” he added.
Pauline Vetter, MD, an infectious disease specialist at Geneva University Hospitals, questioned whether antibody titers can be used to estimate an individual’s level of resistance to the virus. There is some evidence that higher titers correlate with better protection, but it’s not clear to what degree, she said.
“There’s no definitive cutoff,” Dr. Vetter said in an interview. “I can’t say if you have more than a titer of 5, then you’re protected or you’re more protected – or if you have less, then you’re not protected.”
Testing to see whether a person has any S IgG antibodies at all following a vaccination might be worthwhile, she said. She noted that people who know that they did not have an antibody response may be more careful.
Dr. Vetter concluded that not enough is yet known to recommend a third dose or booster for people whose immunity is suppressed.
“There might be a benefit in these populations. But the question is, when and in which situations?” she said.
Dr. Vetter and Dr. Safadi have disclosed no relevant financial relationships.