People who have undergone a solid organ transplant and who
received the Pfizer or Moderna COVID-19 vaccines should receive a third dose,
the US Centers for Disease Control and Prevention (CDC) recommended last week.
The recommendation also applies to people who are receiving treatment
for liver cancer and to people with HIV with low CD4 counts.
The decision follows approval of third doses of the Pfizer
and Moderna vaccines by the US Food and Drug administration. French and British health authorities have already issued recommendations for third booster doses for immunocompromised people and transplant recipients respectively.
The recommendation does not apply to recipients of the
Johnson & Johnson single-dose vaccine. CDC said that there are not
sufficient data to make a recommendation yet.
Immunocompromised people have weaker responses to vaccination
with many types of vaccine.
people are those who have:
- been receiving active cancer
treatment for tumors or cancers of the blood
- received an organ transplant
and are taking medicine to suppress the immune system
- received a stem cell
transplant within the last 2 years or are taking medicine to suppress the
- moderate or severe primary
immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)
- advanced or untreated HIV
- active treatment with
high-dose corticosteroids or other drugs that may suppress your immune
In its recommendations, US CDC drew attention to two studies
showing that a high proportion of those hospitalised with COVID-19 after being
fully vaccinated are immunocompromised.
study of COVID-19 hospital admissions at 18 academic medical centres between
March and May 2021 identified 45 cases of COVID-19 in fully vaccinated
people; 20 (44% of the total) cases occurred in people who were
immunocompromised. Seven of these cases occurred in people who had undergone a
solid organ transplant. By matching COVID-19 cases to hospital admissions for
respiratory complaints or other disorders in people who tested negative for
SARS-CoV-2, the investigators estimated that the effectiveness of the Pfizer and
Moderna vaccines against severe illness was 86.9% but was reduced to 51.9% in
people with a solid organ malignancy or transplant.
study of COVID-19 hospital admissions at 17 hospitals in people fully
vaccinated with the Pfizer vaccine identified 152 cases, 60 in immunocompromised
people. Sixteen of these cases occurred in solid organ transplant recipients;
only three cases in transplant recipients were classified as severe.
Public Health England has also reported on COVID-19 hospitalisations in around 39,000 people who have undergone transplants in England. Between December 2020 and June 2021, 76 people contracted COVID-19 two weeks or more after second vaccine dose. Of these 8% (6) died within 28 days of a positive COVID-19 test
US CDC says that a booster dose should be given at least
four weeks after the second dose of the Pfizer or Moderna vaccines.
However, a small case series of
30 transplant recipients with negative or weak responses to the Moderna or
Pfizer vaccines showed that two-thirds of those with negative antibody levels
prior to a third booster dose (24 of 30) still had negative antibody levels two
weeks after the booster dose. Those with weak antibody levels prior to boosting
(6/30) achieved high antibody levels after boosting. In this study, 15 of the
30 patients received a booster dose with a different type of vaccine, the
Johnson & Johnson adenovirus-vectored vaccine.
However, a larger study in 101
solid-organ transplant recipients (including 12 liver transplant patients) who
received a third booster dose of the Pfizer or Moderna vaccine found that 26
out of 59 people (44%) who had negative antibody responses prior to the booster
developed antibody responses after the third dose.
Neither study looked at cellular immune responses, which play
a key role in preventing severe illness. Although cellular immune responses are
reduced in immunocompromised people, different causes of immunosuppression may
have different effects on cellular immunity. More research is needed to determine
whether cellular immune responses to SARS-CoV-2 vaccination is less strong in
transplant recipients and how cellular immune responses to vaccination affect
the subsequent risk of infection or illness.