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FDA Allows Covid Boosters Targeting Omicron BA.5 Variant

Medical staff prepare a booster dose of Pfizer’s coronavirus disease (COVID-19) vaccine at a vaccination center in Brussels, Belgium January 5, 2022.

Yves German | Reuters

The Food and Drug Administration has authorized Covid boosters targeting the omicron BA.5 sub-option as the US braces for another spike in infections this fall and winter.

The FDA has approved an updated vaccine formula for the first time since the original vaccines were released in December 2020. Pharmacies are expected to start rolling out new boosters after Labor Day weekend.

According to the US Department of Health and Human Services, 171 million doses of updated Pfizer and Moderna shots have been received in the US to date.

The new Pfizer booster dose is approved for people aged 12 and over, while the new Moderna shots are approved for adults aged 18 and over. Eligible age groups can receive boosters two months after the end of the main series or the last old booster.

The Centers for Disease Control and Prevention must approve booster packs before pharmacies can distribute them to patients. An independent CDC advisory committee is scheduled to meet Thursday and Friday to review the data and make recommendations to healthcare providers.

Bivalent vaccines

Public health officials believe the upgraded boosters will provide longer-term protection against the virus and reduce hospitalizations this fall and winter. The new boosters target both the original strain that appeared in China more than two years ago, which scientists call “wild type”, and omicron BA.4 and BA.5, which are currently the dominant variants in the US.

Vaccines that target two different strains are called bivalent vaccines.

Vaccine manufacturers have developed original vaccines against the Covid strain that first appeared in Wuhan, China in 2019. But since then, the virus has mutated greatly. Omicron and its sub-variants have diverged so far from the original strain of Covid that the virus is able to elude protective antibodies induced by vaccines.

As a consequence, the effectiveness of vaccinations in preventing infections and minor illnesses declined substantially as the virus progressed. While vaccines generally still prevent serious illness, the protection from hospitalization they provide has also weakened over time.

“Effectiveness in terms of hospitalization and severe illness is decreasing. The challenge is getting Americans to get immunized regularly,” said Dr. Peter Hotez, an infectious disease expert at Baylor College of Medicine in Texas. Hotez led the team that developed a Covid vaccine based on a protein technology allowed in India.

19% effective

About 76% of people aged 12 years and older received their first two doses of the vaccine in the US, according to the CDC. About 50% of these people received their first booster dose.

For adults 18 years of age and older, three doses of the original Pfizer or Moderna vaccines were 55% effective in preventing hospitalization from the omicron BA.2 subvariant four months after the third vaccination. according to CDC.

Three vaccinations were 19% effective in preventing omicron infection five months after the third vaccination. according to CDC from August 2021 to May 2022. The rapidly expanding sub-variants BA.4 and BA.5 have since pushed omicron BA.2 out of circulation.

The Biden administration moved quickly over the summer to get an updated cadre ready for the fall. Public health officials are concerned that the US is on the cusp of a new wave of infections as more transmissible omicron variants proliferate, immunity from original vaccines wanes, and people head indoors to escape the cold.

Pfizer and Moderna originally developed boosters for micron BA.1, the variant that caused a massive wave of infections last winter. But in late June, the Food and Drug Administration (FDA) advised vaccine makers to switch and target BA.4 and BA.5 instead, as those options quickly caught on. The sudden change in plans left little time for human clinical trials before the fall rollout.

As a consequence, data on the immune response elicited by the new boosters are based on clinical trials of the BA.1 vaccine in humans. In June, Pfizer also presented data to the FDA’s Independent Vaccine Advisory Committee showing that inoculations with BA.5 bivalent omicron increased infection-protective antibodies in mice by about 2.6 times that of the parent vaccine.

Mouse data

Dr. Peter Marks, who heads the FDA’s office in charge of vaccines, said the regulator has a lot of experience changing strains for flu vaccines and is confident in the data used to support approval for BA.5 shots.

According to the FDA, the most common side effects in human trials of BA.1 vaccines were pain, redness, swelling at the injection site, fatigue, dizziness, muscle pain, joint pain, chills, nausea, vomiting, and fever. Covid vaccines also have a well-established safety profile after being administered to millions of people during the pandemic, according to the FDA.

But some infectious disease and vaccine experts say the FDA should have waited for people’s data from BA.5 shots before allowing them. Dr. Paul Offit, a member of the FDA’s advisory committee, said evidence based on mouse studies is not enough to justify approval of the new boosters.

“You have to show some evidence in people that the immune response you get with a bivalent vaccine is clearly better, and that data hasn’t been presented,” said Offit, an infectious disease and vaccine expert at the Children’s Hospital of Philadelphia. .

Human trials

“You can’t ask millions of people to get this booster dose without providing some data on people who show a dramatic increase in neutralizing antibodies to BA.4/BA.5 strains compared to ancestral-type revaccination,” Offit said. , referring to currently allowed snapshots based on the Covid version that emerged in China over two years ago.

Michael Osterholm, lead epidemiologist and director of the Center for Infectious Disease Research and Policy at the University of Minnesota, also said more data needed to be presented on how BA.5 vaccines work in people.

“It’s not that I don’t think it can work,” Osterholm said. “But I think first we need data to show that the immune response to this vaccine is equivalent to or better than what we already have.”

But CDC director Dr. Rochelle Walensky, in a radio interview, said that a longer wait for human data from BA.5 shots could mean the boosters would become obsolete if a new option comes along. Walensky said the change in the vaccine formula is small and should not affect safety.

“There’s always the question of being too slow or too fast,” Walensky told Health Conversations in a radio interview. “One of the problems is if we wait for this data to appear in human data. […] we will be using what I consider to be a potentially obsolete vaccine.”

Dr. Arnold Monto, acting chairman of the FDA’s independent vaccine evaluation committee, said BA.1 shots are very similar to BA.5 boosters. Monto said the Food and Drug Administration (FDA) used the same process they use to change the strain of flu vaccines, in which they often rely primarily on data from ferrets.

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