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Moderna is studying adding booster doses to its vaccine regimen after finding its Covid-19 vaccine was less potent against a coronavirus variant that was first identified in South Africa, the company said Monday.

In lab research that involved testing whether blood from people who had received the vaccine could still fend off different coronavirus variants, scientists found that there was a sixfold reduction in the vaccine’s neutralizing power against the variant, called B.1.351, than against earlier forms of the coronavirus, Moderna reported.


There was no loss in neutralization levels against a different variant, called B.1.1.7, that was first identified in the United Kingdom. Both variants are thought to be more transmissible than other forms of the SARS-CoV-2 virus.

Moderna said that despite the reduction in neutralizing antibodies against B.1.351, the antibody levels generated by its vaccine “remain above levels that are expected to be protective.” Still, it said it was going to start testing whether adding a booster dose to its existing two-dose regimen could increase the levels of neutralizing antibodies even further, and that it was going to start investigating a booster specifically designed against B.1.351.

“These lower titers [of antibodies against B.1.351] may suggest a potential risk of earlier waning of immunity to the new B.1.351 strains,” Moderna said.


The announcement from Moderna gets at a nuance that scientists have been trying to stress as fears around vaccines and variants grew. Both the Moderna vaccine and the immunization from Pfizer-BioNTech produce such powerful levels of immune protection — generating higher levels of antibodies on average than people who recover from a Covid-19 infection have — that they should be able to withstand some drop in their potency without really losing their ability to guard people from getting sick.

“There is a very slight, modest diminution in the efficacy of a vaccine against it, but there’s enough cushion with the vaccines that we have that we still consider them to be effective,” Anthony Fauci, the top U.S. infectious diseases official, said Monday on the “Today” show.

The coronavirus has been evolving throughout the pandemic, and scientists had expected that eventually, the virus would change so much that vaccines would need to be upgraded to better match dominant variants. But the appearance in recent months of the variants, which picked up mutations at much higher rates than the coronavirus was adding at the beginning of the pandemic, has moved up the date at which that might need to occur.

Experts say they need to now figure out how much less effective the vaccines can get before upgrades are needed, and what the regulatory process for approving such tweaks would look like.

Pfizer and BioNTech scientists have already reported their vaccine holds up against B.1.1.7, though they have not reported data yet against B.1.351. But researchers have been more concerned about B.1.351 because it contains a different set of mutations that, at least in lab experiments, had already helped the virus evade some of the immune protection generated in people who had an initial Covid-19 case.

Some of those same mutations of concern also appear in a different variant first seen in Brazil, called P.1.

In the meantime, if mutations do arise that deliver a blow to the vaccines’ strength, experts still say people should get them. Having some immune memory to the virus (which vaccines provide, almost like a substitute for an initial infection) is better than being completely vulnerable. You might still be able to get infected, and maybe even get sick, but giving your immune system even a small edge can reduce the chances you’ll get seriously ill.

Clarification: The headline on this story was updated to better reflect the company’s announcement. 

  • “Moderna’s vaccine is less potent against one coronavirus variant but still protective, company says”… BASED ON WHAT!!!!!!!!!!!!!!!! How can these companies state ANY percentage of efficacy for an UNTESTED VACCINE with a straight face! They don’t even come close to doing the sort of testing that the scientific method demands for determining that this vaccine works AT ALL! It is ALL BS, and I wouldn’t touch it with a 36 foot pole!

  • With the arrival of the Brazilian variant, all bets are off. It is not impossible, since they have identified the variant only in a “Patient Zero” who actually traveled to Brazil, IF that person was very, very circumspect about avoiding people, and with a hyper aggressive contact tracing investigation, they might contain it.
    I hope doctors and medical people will contact the CDC and tell them our “quarantine” procedures are completely inadequate. Per news reports, a traveler must test negative before getting on a plane, then after arriving (not clear what is done in the US to screen) is “required” to quarantine for 7 days here.
    Obviously, the interval between the test in the departure country is too soon – a person could get infected before leaving, or in the airport itself, and still have no symptoms (IF they ever show any) upon arrival in the US.
    Furtthermore, the quarantine in the US is totally on honor system, apparently. No one is locked up, as they are (in hotel rooms) upon arriving in Taiwan.
    Citizens are told to quarantine, again on honor system, for 7 days.

    Please, doctors, nurses, scientists – someone get to CDC and tell them this is inadequate. I fully realize we are going to get this variant – we are apparently just too short-sighted and selfish and stupid to not – but any delay in getting it could be of immense value if the vaccines truly can be tuned up to protect us. Even a few weeks might make a huge difference.

    All indications are, we are going to be playing Whack A Mole with new variants for a long time – leaving aside possible animal reservoirs, the human population will have plenty of infected people for variants to arise in.

    We have to play it better, and actually hit the mole instead of hit where he used to be, too late.

    I hope everyone can contact people in charge and explain to them the need for strict travel restrictions – ho honor system, quarantine enforced by police of some type which apply to US citizens – most travelers probably ARE US citizens, so not applying it to ourselves is just dumb.

  • I also agree with your comment, Doug. Hi Stats News editors and Mr. Joseph, I normally respect the accurate and non-sensationalistic tone of most of Stat News reporting. Please resist the temptation to resort of click-bait headlines that may confuse and mislead readers who may not have the benefit of reading the preprint on Biorxiv.

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