Pfizer Inc. on July 28 raised the 2021 sales forecast for the company’s Covid-19 vaccine by 29 percent to $33.5 billion, and said the drugmaker believes people will need a third dose of the shot developed with German partner BioNTech to keep protection against the virus high.

Moderna Inc. is in talks with U.S. regulators to expand the size of an ongoing trial testing the company’s Covid-19 vaccines in children aged between 5 and 11 years, the drugmaker said on July 26.

A mixed vaccination of first AstraZeneca and then a Pfizer Covid-19 shot boosted neutralizing antibody levels by six times compared with two AstraZeneca doses, a study from South Korea showed.

A longer gap between doses of Pfizer’s Covid-19 vaccine leads to higher overall antibody levels than a shorter gap, a British study found on July 23, but antibody levels are not sustained for long after the first dose.

Two doses of Pfizer or AstraZeneca’s Covid-19 vaccine are nearly as effective against the highly transmissible Delta coronavirus variant as they are against the previously dominant Alpha variant, a study published on July 21 showed.

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.