The US Food and Drug Administration (FDA) is expected to authorize new COVID-19 booster shots designed to fight against the Omicron variants BA.4 and BA.5. As the agency is evaluating data from preclinical studies in mice, experts say health risks are low. However, this strategy could discourage vaccine-hesitant people from getting a jab.
Vaccine developers Pfizer/BioNTech and Moderna announced last week they have completed a submission to the FDA requesting Emergency Use Authorization (EUA) of bivalent booster doses designed to fight the original SARS-CoV-2 strain and Omicron variants BA.4 and BA.5.
Pfizer seeks vaccine authorization in individuals 12 years and older, while Moderna's booster shot is for adults over the age of 18.
Companies followed the guidance of the FDA and submitted clinical data from bivalent Omicron BA.1-adapted vaccine and data from a preclinical trial in mice from Omicron BA.4/BA.5-adapted vaccine.
Omicron BA.4 and BA.5 variants account for more than 90% of cases in the US and are 4.2-fold more resistant to antibodies stimulated by RNA vaccines than previous variants of Omicron.
Politico sources say the FDA is expected to authorize the booster shots as soon as Wednesday, so the updated vaccines could be offered shortly after Labour Day. The US government has procured 175 million doses of bivalent COVID-19 vaccines for a planned fall and early winter campaign.
"Making the trend worse"
Dr. Isaac Weisfuse, adjunct professor in the Master of Public Health program at Cornell University College of Veterinary Medicine, says developing the vaccines against new variants and already manufacturing them is a positive thing.
However, he says, relying on preclinical studies is "shaky" because what works in mice does not necessarily work in people. In addition, it would hit a nerve with many people who are not necessarily against vaccines but have doubts.
"One of the challenges the US has faced is that not everybody has gotten vaccination, and not everybody has gotten boosters. So this may exacerbate that trend or make it worse because people will look at this and say – why are they doing that?" Weisfuse said to Healthnews.
The UK chose a different path and became the first country in the world to authorize Moderna's bivalent vaccine booster shots, targeting both the original strain of the virus and the original Omicron variant BA.1.
According to the UK's health authorities, the bivalent vaccine also generates a good immune response against the Omicron variants BA.4 and BA.5.
Allison Krug, an epidemiologist, says that for people who have already recovered from Omicron or a previous variant, additional boosters may not serve much purpose, as they already have mucosal immunity, providing airway defenses. In addition, those previously infected have systemic immunity, just as people who were vaccinated.
After the FDA's authorization, the Centers for Disease Control and Prevention (CDC) will have to issue a recommendation on using the booster doses targeting the Omicron variants BA.4/5.
Currently, the CDC recommends getting one booster dose for all individuals five years and older. Two booster doses are recommended for adults over the age of 50 and some immunocompromised individuals 12 years and older.
A warning against the mandate
Weisfuse says the updated booster shots are unlikely to cause significant side effects even if they lack data from human clinical trials because manufacturers use the same technology as in late 2019.
"I do not foresee that there will be negative effects, but the question becomes, is it helpful?"
Mansoor Amiji, distinguished professor at Northeastern University's Department of Pharmaceutical Sciences, notes that as mice cannot contract COVID-19, researchers use "humanized models" of mice that carry a human-specific receptor that is required for the virus to bind.
He says that solely using mice to test a drug does not provide the full picture, but there is much data about the COVID-19 vaccine; therefore, the risks are very low.
The FDA Commissioner, Dr. Robert M. Califf, defended the agency's strategy last week by saying that real-world evidence from the current mRNA COVID-19 vaccines, administered to millions of individuals, show that the vaccines are safe.
"As we know from prior experience, strain changes can be made without affecting safety," he wrote on Twitter.
The biggest health risk Krug, the epidemiologist, sees is the FDA authorization and Advisory Committee on Immunization Practices (ACIP) recommendation for an additional booster dose turning into "a blanket mandate" for all adults.
"Experts are divided on the importance of continuously boosting, especially for those with immunity from prior infection and those in a higher risk group for adverse events — generally younger people, males ages 12-29, and those with a history of SARS-CoV-2 infection. These decisions should be guided by a clinician in the context of an individual's unique health risks and those of his or her household," she said.
Krug says mandating would signal that the clinical data is not compelling enough to convince people of the benefits of boosting and a stronger tool was needed.
3. UK Government. First bivalent COVID-19 booster vaccine approved by UK medicines regulator.
7. CDC. COVID-19 Vaccine Boosters.
8. Northeastern University. Benefits of new COVID-19 booster targeting variants outweigh any potential risks, experts say.