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A professional prepares a dose of Pfizer’s Covid-19 vaccine at the Bangkok hospital on August 9. Thailand is one of the countries to start distributing booster shots to health workers Photo: EFE / EPA / NARONG SANGNAK

The United States Medicines Regulatory Agency (FDA, its acronym in English), authorized Thursday evening (12) the administration of a third dose of Covid-19 vaccines from Pfizer and Moderna for certain people including the immune system is weakened by illness, medical treatment or transplants.

The FDA has updated the authorization for emergency use of these two vaccines to allow the booster dose to be given in immunocompromised patients, especially those who have received a solid organ transplant or those who have been diagnosed with conditions causing an equivalent level of immunosuppression.

“The country has entered a new wave of the Covid-19 pandemic and the FDA is particularly aware that people with immunosuppression are particularly at risk of serious illness,” said Janet Woodcock, acting commissioner of the FDA. “After a careful review of the available data, the FDA determined that this small, vulnerable group could benefit from a third dose of Pfizer-BioNTech or Moderna vaccines,” he explained.

People with weakened immune systems, such as transplant recipients, are less able to fight infectious diseases and are more vulnerable to infections such as Covid-19. The United States Centers for Disease Control and Prevention (CDC) estimates that this population represents less than 3% of adults in the country.

Janet Woodcock clarified that people outside of these groups who have been fully vaccinated are “sufficiently protected and do not need an additional dose of the Covid-19 vaccine at this time.”

The CDC called a meeting this Friday to review the scientific evidence supporting the FDA’s decision and to discuss whether to recommend a booster dose for people with compromised immunity. The committee will also assess the need for additional doses for the rest of the population.

The FDA further recommended that immunocompromised people infected with the coronavirus discuss monoclonal antibody treatment options with their doctors. The United States and Brazil have both authorized the emergency use of certain treatments with monoclonal antibodies in Covid-19 patients in hospitals.

In the United States, Pfizer’s anti-covid vaccine is used in people aged 12 and older, while Moderna’s is distributed to people aged 18 and older. The two mRNA immunizers are given in two doses, and the United States adopts a three-week interval for Pfizer and one month for Moderna. The FDA authorized the application of the third dose of vaccine to the target group at least 28 days after the application of the second.

Some countries have already started giving booster doses of Covid-19 vaccines to the elderly and other groups, based on studies that have shown decreased immunity over time.