• People with psoriasis who take immunosuppressant drugs develop normal levels of antibodies from a COVID-19 vaccination, but many do not develop a detectable T-cell response, according to a new study.
• Participants in the study had received two full doses of the Pfizer COVID-19 vaccine.
• These results highlight the importance of vaccinations for people who take immunosuppressants.

People who take immunosuppressant drugs for psoriasis develop adequate antibody responses to COVID-19 after receiving two full doses of the Pfizer vaccine, according to a new study. However, nearly one-third of study participants did not develop a detectable T-cell response, meaning they lacked the immune cells to kill other cells affected by the virus. The study supports prioritizing additional vaccine doses for people who take immunosuppressant drugs, researchers concluded.

For the study, published Nov. 9 in The Lancet Rheumatology, researchers analyzed how well the immune system responds against COVID-19 in vaccinated people with psoriasis who use immunosuppressant drugs. Researchers at a psoriasis treatment center in London recruited 82 people with psoriasis who take immunosuppressants, including methotrexate and biologics like tumor necrosis factor (TNF) inhibitors, IL-17 inhibitors, or IL-23 inhibitors.

Fifteen people without psoriasis, who were not using immunosuppressants, were also recruited to the study. All of the study participants had received two doses of the COVID-19 vaccine made by Pfizer.

Immunosuppressants and COVID-19 Vaccine Effectiveness

The researchers studied each participants’ immune system 14 days after they received their second vaccine dose. They looked at two different factors:

• Antibodies, the proteins made by the immune system that can disable the COVID-19 virus
• T cells, the immune cells that kill other cells in the body that have been affected by the virus

The study authors found that people using immunosuppressants had similar antibody levels as the control participants who were not using these drugs. These antibodies were able to fight off infections by the original COVID-19 virus strain as well as the alpha and delta variants. This shows that the drugs did not affect the immune system’s ability to make antibodies.

However, the researchers found differences in how T cells reacted to the vaccine. All of the healthy controls had a “T-cell response” — their T cells responded to virus proteins by making molecules that help the immune system fight off COVID-19. Most people taking immunosuppressants (62 percent of people using methotrexate and 74 percent of people using biologics) also had a T-cell response. Overall, though, nearly a third of participants on immunosuppression had no detectable T-cell response.

One Vaccine Dose Is Not Enough

The study authors commented that a full two-dose round of vaccination may not protect against COVID-19 long-term for people using these drugs. “Cellular immunity might diminish over time in some immunosuppressed individuals despite a second vaccine dose,” the authors wrote. Additional research needs to be undertaken in order to better determine how well vaccines can protect against COVID-19 in people using methotrexate or biologics.

A previous study by the same authors analyzed the immune system response in people on immunosuppressants after one Pfizer vaccine dose. This study found that people using methotrexate had fewer antibodies after a single dose. However, the new study found that two doses of the vaccine were enough to normalize antibody levels. These results highlight the importance of getting two vaccine doses for people on immunosuppressants.

In the United States, all adults are eligible to receive a booster dose of all three COVID-19 vaccines. Those who received the Pfizer or Moderna vaccine are eligible for a booster at least six months after their second dose and those who received the Johnson & Johnson vaccine are eligible two months after receiving the single-dose vaccine.

Individuals who are considered immunocompromised — including those who take immunosuppressant drugs — are eligible to receive a third dose of the Pfizer or Moderna vaccines at least 28 days after the second dose.