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Vaccine Doses: Is 3 better than 2?

 Organ Transplant Recipients Receive 3 Vaccine Doses
    
    As of July 13, 2021, 159 million Americans or 48.5% of the U.S. have been fully vaccinated for COVID-19. Most of these individuals will produce the antibodies needed to fight off COVID-19 infection in response to coronavirus exposure. However, some recipients of the vaccine, like the immunocompromised, produce little to no antibodies in response to vaccines or infection. Immunocompromised individuals commonly consist of blood cancer survivors, organ transplant recipients, and those taking drugs that kill or block B cells, which produce the antibodies needed to fight an infection. Previously, a study published in March 2021 investigated the effects of one dose of the Pfizer vaccine on organ transplant recipients. Only 17% of the study group produced detectable antibody levels three weeks after vaccination. (See Immunocompromised Individuals and the COVID-19 Vaccine) Antibody responses in transplant recipients were also found to be significantly reduced after 2 doses of an mRNA vaccine. So, what else can be done so that the immunocompromised produce sufficient antibodies? In June 2021, a study published in the Annals of Internal Medicine investigated the effects of three doses of the COVID-19 vaccine on organ transplant recipients. 

About the Study

    The study, which was approved by the Johns Hopkins institutional review board, involved 30 solid-organ transplant recipients with a median age of 57 years. Of the participants, 17 were women and 1 identified as non-white. All participants had previously received two doses of an mRNA vaccine: 57% of patients received two doses of the  Pfizer vaccine and 43% received two doses of the Moderna vaccine. The median time between transplantation and initial vaccination was 4.5 years. All participants were tested for COVID-19 antibodies at a median of nine days before receiving a third vaccine dose: 24 participants had negative antibody levels and 6 had low-positive antibody levels. Study participants received a third dose a median of 67 days after their second dose: 15 received a Johnson and Johnson vaccine, 9 received the Moderna vaccine, and 6 received the Pfizer vaccine.

Study Results

   Participants were tested for antibody levels a median of 2 weeks after receiving a third vaccine dose. All 6 patients who had low-positive antibody levels prior to the third dose had high-positive antibody levels after the third dose. Of the 24 patients who had negative antibody levels prior to the third dose, 6 had high-positive levels after the third dose, 8 had low-positive levels and 6 remained at negative levels. Fifteen participants reported mild or moderate local reactions to the vaccine and 14 reported fatigue. 

Similar Study and Implications

   A similar study published in the New England Journal of Medicine in June 2021 tested the effects of three doses of the Pfizer vaccine on organ transplant recipients. While only 40% of the 99 study participants had COVID-19 antibodies between their second and third dose, 68% of participants had detectable COVID-19 antibodies four weeks after a third dose of the Pfizer vaccine. There were no cases of COVID-19 reported in any of the patients.


    The two study results suggest that a third dose of the COVID-19 vaccine in transplant recipients offers increased protection against the virus with only minimal side effects. However, further studies and clinical trials are still needed to determine and confirm the safety and immunogenicity of three vaccine doses in transplant recipients. Nevertheless, a large proportion of the immunocompromised still remain at risk for the coronavirus so it's important that those who are eligible to get vaccinated do so. 

Sources

1. Werbel, William A., et al. “Safety and Immunogenicity of a Third Dose of SARS-CoV-2 Vaccine in Solid Organ Transplant Recipients: A Case Series.” Annals of Internal Medicine, 15 June 2021, doi:10.7326/l21-0282.

2. Kamar, Nassim, et al. “Three Doses of an MRNA Covid-19 Vaccine in Solid-Organ Transplant Recipients.” New England Journal of Medicine, 23 June 2021, doi:10.1056/nejmc2108861.

Comments

  1. Laura BushJuly 27, 2021 at 1:04 PM

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