Scientists back third doses of Pfizer and AstraZeneca after studies showing drop in antibodies

As the scientific debate continues on whether or not a third booster dose of COVID-19 vaccines is necessary, several countries are already preparing to adopt measures in this regard. Spain’s Health Minister Carolina Darias assured this Friday that they are likely to decide to apply a third dose of the vaccine to increase protection against the disease, Israel announced that it would follow this criterion in immunocompromised patients and a similar decision was adopted. in the last hours of Uruguay, while British scientists backed the booster proposals in the fall, after blood tests on hundreds of people revealed that protective antibodies can drop dramatically in the weeks following the administration of the second vaccine.

In developed countries, the appearance of new variants of the coronavirus, in particular Delta, which has gained the upper hand since last April, and the ignorance of the duration of the vaccine’s protection has led some scientists to further study the possibility of apply the booster dose.

In early July, the pharmaceutical company Pfizer argued that recent data obtained in Israel revealed that, compared to the response to the Alpha variant, the vaccine’s effectiveness in protecting against the symptomatic disease caused by the Delta variant had decreased by more than 90% to 64%. He added that in his experiments a third dose produced levels of neutralizing antibodies 5 to 10 times higher than those which occurred after the second dose, and he predicts that the third dose can be given 6 to 12 months. after the second.

But controversy erupted in early July when Pfizer announced that it would seek authorization to initiate a booster dose. Quickly, the US Centers for Disease Control and Prevention (CDC) and the Drug Regulatory Authority (FDA) said in a joint statement that “until now, there was no need for a third dose for the American population. “

The CDC has partly changed its position, since yesterday agency officials admitted they were looking to explore this possibility.

The World Health Organization (WHO) and groups defending the human right to health have followed this approach, saying care must continue to focus on delivering the first doses to the world’s most vulnerable. Until this month, only 25.4% of the world’s population had access to a single dose of the COVID-19 vaccine. In low-income countries, only 1% of the population received a dose. “The global gap in vaccine supply is extremely uneven and inequitable,” said the WHO Director-General Tedros Adhanom Ghebreyesus.

Study UCL virus monitoring, a British official body monitoring the progress of the pandemic with data, found that the antibodies generated by two doses of the Oxford-AstraZeneca and Pfizer-BioNTech vaccines began to decline six weeks after the second injection. In some cases falls by more than 50% by the 10th week.

Researchers guarantee both vaccines are highly effective against COVID-19, but say the results support plans for a booster campaign starting in the fall, especially for those who were vaccinated at the start of the campaign with the AstraZeneca injection.

Drops in antibodies are expected after vaccination and don’t necessarily mean people are more vulnerable to the disease, but researchers fear that if the drops persist, the effectiveness of the vaccines could decrease.

“We know that antibody levels start at a high level and drop dramatically,” said Professor Rob Aldridge, infectious disease epidemiologist at University College London (UCL). “We’re concerned that if they continue to decline at the rate we’ve seen, the protective effects of vaccines will also start to wear off, and the big question is when will that happen? “

Last month, the Interim Council of the Joint Committee on Vaccination and Immunization (JCVI) urged the UK’s National Health Services (NHS) to prepare for a booster program in the fall, but no final decision has been taken on the progress of the measure. It is not known whether vaccine protection has weakened enough to warrant boosters, and many experts argue that doses are needed more urgently in other countries.

The UCL team analyzed the blood of 605 vaccinated people, mostly in their fifties and sixties. They found that antibody levels varied widely between patients, but a double dose of Pfizer-BioNTech tended to produce significantly more antibodies to the coronavirus than two injections of the Oxford-AstraZeneca vaccine.

Three to six weeks after complete vaccination with Pfizer, antibody levels have generally remained at about 7,500 units per milliliter (ml), but have more than halved to 3,320 units per ml after 10 weeks. For AstraZeneca, antibody levels peaked at around 1,200 units per ml and generally dropped to 190 units per ml after 10 weeks. Since publishing the results in a letter to The Lancet, researchers have seen the same trend in 4,500 other study participants.

Although antibody levels are important for protection, the immune system has other defenses that form after infection or vaccination. It is normal for antibody levels to decrease over time and for the immune system to “remember” the infection from memory B cells. If the virus invades, these cells quickly produce antibodies to the virus. Additional protection comes from T cells, which destroy infected cells and limit the severity of the disease.

“Antibodies aren’t 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 this data supports JCVI’s case for reinforcements, with priority for clinically vulnerable people, people over 70 and all people living in nursing homes for the elderly.”

The findings have been reviewed by the JCVI, but are unlikely to have a major impact on the driver discussions. The loss of antibodies is a warning sign that vaccines may wear off over time. but he doesn’t say when that moment comes. Public health officials won’t know for sure until people who received their second injection at the start of the vaccine rollout start showing up in hospitals. A decision on the timing of the recalls is expected before this happens.

“The decline in antibody responses over time may support booster strategies, particularly 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, hepatologist at the University. from oxford . “However, even with low levels of antibodies, memory B cells and T cells can protect well against serious disease.”

But he said the administration of boosters would ideally be based on more evidence, as their need in the UK “must be balanced with fair administration of the first and second doses of vaccine around the world.”

Professor Matthew Snape, a vaccine specialist at the University of Oxford, said that “Studies like this do not in themselves provide evidence of decreased vaccine protection, but they are really important to us. help understand what happens if population-based studies show decreased protection with increasing time since vaccination.

“A decrease in blood antibodies is to be expected after vaccination, and does not necessarily correspond to an increased risk of disease. Protection against infection may very well depend on the presence or absence of antibodies in the respiratory lining, and T cells may provide protection against progression to serious disease after infection.

“However, it is clear that continued protection against vaccines for months or years after vaccination cannot be assumed, hence the importance of continuous surveillance for any increase in breakthrough infections”, a- he declared.

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