The level of protection provided by Moderna’s COVID-19 vaccine is nearly as high at six months as it is right after vaccination, but the company said vaccinated people will still need booster shots before the end of the year.

“A dose three of a booster will likely be necessary to keep us as safe as possible through the winter season in (the) Northern Hemisphere,” Moderna President Stephen Hoge told investors, according to a FactSet transcript of the company’s Thursday earnings call.

Hoge cited the widely circulating delta variant, which is more than two times as contagious as the original strain of the virus, and the company’s understanding that vaccine-induced immunity may wane.


 said the efficacy rate for its COVID-19 vaccine stands at 93.2% four to six months after vaccination.

Pfizer Inc.
on the other hand, said last week that protection from its COVID-19 shot begins to decline within two to three months. The vaccine it developed with BioNTech SE

has an efficacy rate of 96.2% for the first two months, before falling to 90.1% through the fourth month, and then further declining to 83.7% through the sixth month. 

Both vaccines are mRNA-based shots that require two doses and had nearly identical efficacy rates in clinical trials—95.0% for Pfizer, and 94.1% for Moderna.

So, what does this all mean?

Well, to start, the public should understand that both vaccines still provide very strong protection against the virus, and people who received either shot can continue to remain secure in the vaccines’ ability to largely prevent severe illness. More importantly, the shots are very good at making sure people don’t end up in the hospital or die if they do get sick with a breakthrough infection.

Moderna also said this week its shot has 98.2% efficacy at preventing severe disease and completely protects against death.

As time passes, more data will emerge that is expected to differentiate the Moderna and Pfizer vaccines. This could include different efficacy rates, as we’re seeing now; how well the vaccines protect against different variants; and how often someone may need a boost to retain immunity levels, according to Cody Powers, a COVID-19 vaccine expert at ZS, a pharmaceutical consulting firm.

The debate over boosters

The additional context provided by Moderna executives this week about its COVID-19 vaccine underscores how complicated the national discourse about booster shots is becoming.

Over the last month or so, Pfizer has very publicly called for the need for booster shots, citing preliminary data out of Israel. On July 8, the Centers for Disease Control and Prevention and the Food and Drug Administration put out a statement saying that fully vaccinated Americans do not need an extra dose of vaccine. The National Institutes of Health director told staff in an email that week that Pfizer had gotten ahead of itself talking about the need for boosters.

This is already changing.

Dr. Anthony Fauci, chief medical adviser to President Joe Biden, on Thursday told reporters that “it is extremely important for us to move to get [immunocompromised] individuals their boosters. We are now working on that, and we’ll make that be implemented as quickly as possible because for us and for the individuals involved it is a very high priority.”

In some cases, people who got Johnson & Johnson’s

vaccine, which is less effective than the mRNA shots, went and got mRNA shots to “boost” their own immunity. The city of San Francisco is allowing people who were initially vaccinated with the J&J shot to get a dose of an mRNA vaccine.

Such “off-label” boosting isn’t condoned by federal officials. White House press secretary Jen Psaki said Wednesday that doing this “is not in alignment with the guidance of public health officials.”

The World Health Organization this week said countries should not give booster doses until the end of September so that at least 10% of the world’s population can be vaccinated, a statement that the Biden administration took issue with.

“Admittedly, the discussion on boosters is complex, given [the] mix of clinical, regulatory, ethical, and geopolitical considerations,” Powers said in an email. “Companies would be weighing all factors when deciding how to approach the subject.”

There are no formally authorized booster shots in the U.S. at this time, though Pfizer is expected to submit an application to the Food and Drug Administration for its COVID-19 booster sometime this month.

Moderna and Pfizer have said that boosters should be given as early as six to eight months after completing the initial vaccination series.

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