Delayed administration of the second dose of an mRNA COVID-19 vaccine leaves most cancer patients unprotected, a new report warns.
In clinical trials last year, the messenger RNA vaccines were tested with second doses given either three or four weeks after the first depending on the vaccine.
In January, the UK decided to delay second doses until 12 weeks. At Kings College London, doctors studied 205 adults who received the Pfizer/BioNTech vaccine, including 151 cancer patients.
After the first dose, almost all the healthy individuals had strong immune responses, but that was true for fewer than half of patients with solid tumors and fewer than one-in-seven patients with blood cancers, said Dr. Adrian Hayday.
When solid-cancer patients got the second dose at the recommended three weeks, 95 per cent developed robust antibody responses.
Among those who did not get the booster dose on time because of the UK’s new policy, only 43 per cent of solid cancer patients and eight per cent of blood cancer patients had antibodies at five weeks.
“A single dose of the vaccine left most cancer patients largely or completely unprotected,” Hayday said.
The study report has been submitted ahead of peer review to medRxiv but is not yet online. The data are available on the COVID-Immuno-Phenotype website.