Scientists are working on a benchmark for Covid-19 vaccine efficacy that would allow drugmakers to conduct smaller, speedier human trials to get them to market and address a huge global vaccine shortage.

Executives from Pfizer met with government health officials to discuss Pfizer and BioNTech’s contention that booster shots for their COVID-19 vaccine will be necessary. 

The United States is reviewing the need for a third Covid-19 booster shot among residents who have already been vaccinated but needs to see more data to know if additional shots could raise people’s risk of serious side effects, a U.S. health official said July 13.

Health agencies and vaccine and immunology experts have pushed back against Pfizer and BioNTech’s assertions that a Covid-19 booster shot is necessary.

Pfizer and partner BioNTech plan to ask U.S. and European regulators within weeks to authorize a booster dose of the companies’ Covid-19 vaccine, based on evidence of greater risk of infection six months after inoculation and the spread of the highly contagious Delta variant.

The World Health Organization said on Friday that it was not clear whether Covid-19 booster vaccines will be needed to maintain protection, until further data is collected.

A third shot of the Oxford-AstraZeneca Covid-19 vaccine produces a strong immune response, researchers said on June 28, adding there was not yet evidence that such shots were needed, especially given shortages in some countries.

Infectious disease experts are weighing the need for booster shots of the Pfizer/BioNTech or Moderna mRNA-based vaccines for Americans who received Johnson & Johnson’s one-dose vaccine due to the increasing prevalence of the more contagious Delta coronavirus variant.

The World Health Organization (WHO) forecasts that people most vulnerable to Covid-19, such as the elderly, will need to get an annual vaccine booster to be protected against variants, an internal document seen by Reuters shows.

Pfizer Inc. began testing fully vaccinated adults over 65 in a new study that uses the company’s 20-valent pneumococcal conjugate.