COVID-19 vaccine developers are making increasingly bold claims that the world will require yearly booster shots or new vaccines to combat concerning coronavirus variants, but some scientists question when, or whether, such shots will be required.

Some of these scientists expressed concern that public expectations for COVID-19 boosters are being set by pharmaceutical executives rather than health specialists, though many agreed that preparing for such a need was prudent.

They are concerned that a push by wealthy countries for repeat vaccination as early as this year will widen the gap with poorer countries, which are struggling to buy vaccines and may take years to inoculate their citizens even once. According to O’Brien, the WHO is putting together a panel of experts to review all variant and vaccine efficacy data and make recommendations for changes to vaccination programs as needed.

Pfizer Inc CEO Albert Bourla has stated that people will “likely” require a booster dose of the company’s vaccine every 12 months, similar to an annual flu shot, to maintain high levels of immunity against the original SARS-CoV-2 virus and its variants. In response to the criticism, stated that it anticipates the need for boosters while the virus is still widely circulated. According to a company spokeswoman, this could change once the pandemic is under control.

Moderna Inc CEO Stephane Bancel expects a vaccine targeting a variant first identified in South Africa to be available by the fall and anticipates that regular boosters will be required.

The US is preparing to have such doses on hand for Americans, while the European Union, the United Kingdom, and Israel have ordered new supplies of COVID-19 vaccines to be used as protective boosters.

Some health experts, such as Richard Hatchett, CEO of the Coalition for Epidemic Preparedness Innovations (CEPI), which has funded many vaccine projects, believe vaccine makers are correct to plan ahead for boosters given the uncertainty about what will be required in the long run.

Pfizer and its German partner BioNTech SE have discovered that their shot is more than 91 percent effective six months after the second dose, compared to nearly 95 percent in their clinical trial. The companies will monitor how effective the security remains over time.

Pfizer anticipates that the COVID-19 vaccine will be a major revenue contributor for many years, with sales of $26 billion from the shot in 2021. According to IQVIA Holdings, a U.S. health data firm, global spending on COVID-19 vaccines and booster shots could reach $157 billion by 2025.

Moderna President Stephen Hoge anticipates that boosters will be required to maintain high immunity levels, owing in part to vaccine hesitancy, as an estimated 30% of the U.S. population may refuse to be vaccinated. People at high risk of severe illness may need to boost their immune protection as long as the virus is circulating widely, according to Hoge.

Scientists were optimistic late last year that highly effective vaccines could quickly halt the global pandemic that had devastated economies and killed more than 3.4 million people.

Those hopes were dashed by evidence in February that mutant versions of the virus could evade vaccine protection. Laboratory studies revealed that the South African variant could reduce antibody levels by six to eightfold in people vaccinated with the Pfizer or Moderna vaccines.

Data from clinical trials also revealed that vaccines from AstraZeneca Plc, Johnson & Johnson, and Novavax Inc were less effective at preventing infections in South Africa, where the variant is common. These findings prompted pharmaceutical companies to begin testing booster doses of their vaccines and to develop vaccines that target specific variants of the virus.

According to Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID) and a top White House adviser, recent research suggests that the Moderna and Pfizer/BioNTech vaccines produce high levels of protective antibodies, creating a “cushion effect” against the known variants.

Furthermore, antibodies that prevent the coronavirus from attaching to human cells do not tell the entire story. Several studies suggest that T cells, a type of white blood cell that can target and destroy infected cells, may aid in the prevention of severe COVID-19 and hospitalization.

Nonetheless, health officials in the United States, the United Kingdom, and Europe are assuring their populations that a new round of shots will be available if necessary, despite the fact that many countries are still in desperate need of vaccine supplies.