Pharmaceutical executives and federal health officials say people likely will need booster shots to maintain their protection against Covid-19 and emerging coronavirus variants—but developing the boosters may strain the supply chain's capacity to produce other critical drugs and vaccines.

Pharma execs and officials say Americans should expect Covid-19 booster shots

During a virtual event hosted by CVS Health, which aired Thursday but was recorded April 1, Pfizer CEO Albert Bourla said people who have received Covid-19 vaccines will "likely" need a third vaccine dose "somewhere between six and 12 months" after being fully vaccinated, then annual vaccinations to protect themselves against the novel coronavirus as it evolves.

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"There are vaccines like polio where one dose is enough," Bourla said. "And there are vaccines like flu that you need every year. The Covid virus looks more like the influenza virus than the polio virus."

However, Bourla said more research is needed to confirm whether booster shots and annual vaccinations will be necessary, noting "variants will play a key role."

Separately, Moderna President Stephen Hoge has said he expects booster shots will be needed "annually, probably seasonally, even though the pandemic is raging in a nonseasonal way." Moderna executives during a company vaccine event this week predicted countries with high vaccination rates may be prepared to turn their attention toward booster shots by the end of the year.

In addition, David Kessler, President Biden's chief science officer for the pandemic response, during a House subcommittee hearing Thursday said Americans should expect to receive booster shots to protect against coronavirus variants.

"With many vaccines, we understand that at a certain point in time we need to boost, whether that's 9 months, 12 months. And we are preparing for that," Kessler said.

How vaccine manufacturers are exploring the need for booster shots

Pfizer and BioNTech are currently assessing how long their Covid-19 vaccine will protect against the coronavirus. The companies earlier this month said data from more than 12,000 vaccinated participants in their clinical trials suggest their vaccine is more than 91% effective at protecting against Covid-19 and more than 95% effective against severe disease up to six months after people receive their second dose of the vaccine. Similarly, data suggests Moderna's Covid-19 vaccine is highly effective at six months.

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However, researchers have not yet determined how long protection from any of the Covid-19 vaccines will last, and they believe booster shots might eventually be necessary.

In February, Pfizer and BioNTech started testing whether a third dose of their Covid-19 vaccine can protect people against emerging coronavirus variants—some of which appear to be more transmissible, potentially more deadly, and possibly less susceptible to vaccines than earlier variants of the virus.

Meanwhile, NIH in March began testing whether a third dose of Moderna's vaccine could increase protection against the B.1.351 variant first identified in South Africa. Bancel during an interview CNBC's "Squawk Box" said Moderna hopes to submit new data to FDA within a few months to have a booster shot for its vaccine available by the fall.

Ultimately, however, Bancel said he hopes Moderna will be able to develop a two-in-one vaccine to protect people against the seasonal flu and Covid-19. "What we're trying to do at Moderna actually is to get a flu vaccine in the clinic this year and then combine our flu vaccine to our Covid vaccine so you only have to get one boost at your local CVS store ... every year that would protect you to the variant of concern against Covid and the seasonal flu strain," Bancel said.

Biden admin seeks to ensure US will have booster shots if they become necessary

Kessler said the Biden administration is involved "in discussions" with vaccine makers to ensure the United States can secure booster shots if they become necessary.

"We are in discussions right now, making sure that we can secure those vaccines for a boost or variants. We are in that process right now," Kessler told the House Select Subcommittee on the Coronavirus Crisis on Thursday.

However, Kessler said the administration has reached "no decision" on a strategy for administering booster shots because of the uncertainty around the duration of immunity from currently authorized Covid-19 vaccines.

Experts say producing booster shots could lead to manufacturing and supply constraints. For example, a report from the Government Accountability Office released this week showed that using the Defense Production Act to prioritize the production of Covid-19 vaccines has strained manufacturing and supply chain capacity to produce other critical drugs and vaccines, including the seasonal flu vaccine.

And the World Health Organization's Director-General Tedros Adhanom Ghebreyesus said manufacturing booster shots may further delay efforts to distribute first-time vaccinations to people around the globe.

"Global manufacturing capacity and supply chains have not been sufficient to deliver vaccines quickly and equitably where they are needed most. More funding is needed, but that's only part of the solution. Money doesn't help if there are no vaccines to buy," Ghebreyesus said (Lovelace, CNBC, 4/15; Chow, NBC News, 4/15; Hopkins, Wall Street Journal, 4/15; Stankiewicz, CNBC, 4/14; Cunningham, Washington Post, 4/16; Tin, CBS News, 4/16).