Scientists have backed Covid’s booster proposals in the fall after blood tests on hundreds of people revealed that protective antibodies can drop substantially in the weeks after the second vaccine is given.
Antibody drops are expected after vaccination and it doesn’t necessarily mean that people are more vulnerable to the disease, but researchers are concerned that if the declines persist, the effectiveness of the vaccines may decline.
The UCL virus surveillance The study found that antibodies generated by two doses of the Oxford / AstraZeneca and Pfizer / BioNTech vaccines began to decline as early as six weeks after the second injection, in some cases decreased by more than 50% over 10 weeks.
The researchers emphasize that both vaccines are extremely effective against Covid, but say the findings support plans for a booster campaign this fall, particularly for those who were vaccinated early and with the Oxford / AstraZeneca injection.
“We know that antibody levels start out high and go down substantially,” said Professor Rob Aldridge, infectious disease epidemiologist at UCL. “We are concerned that if they continue to decline at the rate that we have seen, the protective effects of vaccines will also start to wane, and the big question is, when will that happen?”
The interim advice of the Joint Committee on Vaccination and Immunization (JCVI) last month encouraged the NHS to prepare for a fall booster program, but no final decision has been made on whether to proceed. It is unclear whether vaccine protection has weakened enough to warrant boosts, and many experts argue that doses are more urgently needed in other countries.
The UCL team analyzed blood from 605 vaccinated people, mostly in their 50s and 60s. They found that antibody levels varied widely between patients, but a double dose of Pfizer / BioNTech tended to produce much more antibodies to the coronavirus than two injections of the Oxford / AstraZeneca vaccine.
Three to six weeks after full vaccination with Pfizer, antibody levels typically remained at around 7,500 units per ml, but more than halved to 3,320 units per ml after 10 weeks. For AstraZeneca, antibody levels peaked at approximately 1200 units per ml and generally dropped to 190 units per ml after 10 weeks. From the publication of the results in a letter to The Lancet, Researchers have seen the same trend in another 4,500 study participants.
While antibody levels are important for protection, the immune system has other defenses that build up after infection or vaccination. It is normal for antibody levels to decline over time and for the immune system to “remember” the infection with memory B cells. If the virus invades, these cells rapidly produce antibodies directed against the virus. Additional protection comes from T cells, which destroy infected cells and limit the severity of the disease.
“Antibodies are not the perfect measure of risk; We don’t know if there is a magic number, so to speak, where the risk of infection or hospitalization becomes significant, ”Aldridge said. “But we believe these data support JCVI’s case for reinforcements, with priority for the clinically vulnerable, those over 70 and all people living in nursing homes.”
The findings have been considered by the JCVI, but are unlikely to have a major impact on discussions of drivers. Loss of antibodies is a warning sign that vaccines may wear off over time, but it doesn’t say when that time comes. Public health authorities won’t know for sure until people who received their second injections early in the deployment start showing up in hospitals. A decision on the booster schedule is expected before that happens.
“Declining antibody responses over time may support booster strategies, especially in the context of a third wave in the UK with the Delta variant, where episodes of infection are now common after two doses of vaccine.” said Professor Eleanor Barnes, a hepatologist at the University. from Oxford. “However, even with low antibody levels, memory B cells and T cells may well protect against serious disease.”
But he said that the administration of boosters would ideally be based on more evidence, as its need in the UK “must be balanced with the equitable administration of the first and second doses of vaccine globally.”
Oxford vaccinologist Professor Matthew Snape said: “Studies like this do not in themselves provide evidence of diminishing protection from vaccines, but they are really important to help us understand what is happening if population-based studies show a decrease in protection with increasing time since immunization.
“A decrease in blood antibodies is to be expected after immunization, and does not necessarily correspond to an increased risk of disease. Protection against infection may well depend on whether or not there are antibodies in the respiratory lining, and T cells can provide protection against progression to serious disease after infection.
“However, it is clear that continued protection from vaccines for months or years after immunization cannot be assumed, hence the importance of continued surveillance for any increase in breakthrough infections.”
George is Digismak’s reported cum editor with 13 years of experience in Journalism