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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. 

  • My husband and I got our first dose of Moderna Vaccine on January15,2021
    We are having a hard time finding a place in SC to get our second dose on February 12th. We have a card with the info on it but we’re told to make our second appointment. The place we got the first dose is closed down. What do we do?
    We are 76 and 80 years old.

    • No, Jeri…that is actually true. No one is being sick here. If you’d like more information about why the responsibility is laid at the feet of the federal government (i.e. the last administration), I highly recommend “Totally under control” on Hulu. It is a documentary that explains this quite well. Stay safe

  • Mr. Joseph- I’m worried your article may lead the average person to misunderstand the situation. From the BioRxiv preprint, the Moderna vaccine produces an immune response that can be diluted to 1/290th — by ALMOST THREE HUNDRED TIMES — and still neutralize the South African variant. THIS IS AWESOME PERFORMANCE and should hearten anyone contemplating taking the Moderna vaccine. (And yes, the vaccine-induced immune response can be diluted even more, by 1852 times, and still neutralize prior virus variants — this is even-better, mind-blowingly phenomenal performance!)

    Instead of trumpeting this success, your article caused another commenter to say, “Very upsetting to hear this after taking my first dose of Moderna Vaccine. I would have opted for the Pfizer had I known.” This is a shame, both because Moderna’s performance is still GREAT, but also because similar data about the Pfizer vaccine is not yet available, and may turn out to be less-good.

    Science communication is difficult — and I know you don’t choose your story’s headline — but please consider asking your editors to change the title to “Moderna vaccine is STILL VERY EFFECTIVE against South African variant” and revise it to not bury the lede with a Fauci quote in the 7th paragraph.

    Thank you for your work reporting in these difficult and complex times.

    • I definitely wouldn’t want the Moderna vaccine, not because of the SA variant but because it hasn’t been tested on long covid patients which the others have. Why would you not test on Long Covid? Sadly here in the UK we don’t get to choose which vaccine we get so I’ll just have to hope it’s not that one. Several people on my Long Covid group from the US have reported feeling worse after having that vaccine whereas most who have had the Pfizer or Oxford ones have been fine.

  • The best mitigation against COVID is to be healthy, but this seems to elude STAT. Healthy people aren’t dying. Unhealthy people are dying. Vitamins, good diet, and exercise will keep you alive and immune system strengtened. Another way to look at the problem of virus variants is to recognize that SARS-2 is mutating faster than we can mitigate against it with a vaccine. Indeed, entering into an escalation war against it may not be the best strategy. This could lead to increased virulence, more deadly. Consider MRSA: many more people die from this in the hospital each year than from COVID because we cleaned so much, and it mutated in response, that it is multidrug resistant, far more deadly. Double masking (Fauci latest suggestion), multiple vaccine shots, turning your home into a hyperbaric chamber — the virus is teaching us an important lesson. It has the upper hand under certain conditions. Best not to play into them.

  • There is nothing in that report that says that the Pfizer BoiNTech vaccne has more efficacy against the S Afr variant (B.1.351) than does the Moderna vaccine. Both are “holding up” against the UK variant (B.1.1.7).
    and Moderna has said they are already modifying their Vaccine to improve efficacy against the SAfr variant. Like the same for Pfizer

  • Anyone doubting the very grave implications of the new variants should look at reports from Manaus, Brazil.
    They had an extreme level of infection in May/June 2020. It subsided a great deal, as expected, because they had herd immunity at that point. One professor from University of Sao Paulo found 66% of population had antibodies.
    But about a month ago, a new huge outbreak took place. It is almost certain it is due to a new variant, and the new variant is infecting people who still have good immunity to the old variant.
    In the US, we have about 1% vaccinated, and despite goals stated by the new President, no clear indication we will get more than about 1% vaccinated per week for the next few months. Despite the 25M cumulative tolls given, we really have had probably more like 75M infected, and herd immunity is what has greatly slowed down the epidemic. But all indications are, the variant in Manaus and South Africa evade the immunity those 75M have – a scarier thought – if young people were protected from the variant of the first wave due to some learned immunity, they may have no protection from this one – the South African health minister said many young people are getting severely ill.

    We need to keep these variants out – the measures described in yesterday’s report Biden had issued “travel bans” for South Africa and Brazil are not adequate.

    As for the Moderna vaccine working against the South Africa variant and their expectation it will work against the Brazil variant – that claim seems very specious right now. I see no citations to any study of a vaccinated group, or even test animals – nothing to indicate it has actually been tested, even on a tiny scale, in vitro.

    Perhaps going forward to vaccinate all we can with the “old” vaccine makes sense right now – we know people are still getting sick with the old variant and we know we need everyone protected against all variants, AND, hopefully, the lessons learned in getting this vaccine out will be remembered for the next one, but we are not going to be anywhere near protected, unless and until it is proven the current vaccines are effective against the new variants, AND we get a lot of them into arms.

    • As was said in another Statnews articles, in the situation with Manaus it’s most probably not just a case of reinfections alone. It’s important not to forget there might be other confounding variables.

      Manaus is just about the worst city in the world for such an outbreak to occur in because most of the population lives in squalid conditions and since it is by the Amazon river, people depend on packet ferry boasts to move around. That is why the infection spread so much in the first place. Cases might be rising against drastically because in these conditions, finding new victims in the periphery of the city is easy for the virus to do.

      Likewise, South Africa has a lot of people living in slums in unsanitary living conditions.

      If you research the E484K from the South African and Manaus variant that people are so scared about, you will see that it was first identified in Rio de Janeiro state in last July and it is still largely confined there after all this time. It does not seem to have led to countless reinfections either.

      A preprint study also showed that it is not all people who showed reduced recognition to E484K but only a portion, and even people who had antibody evasion to that mutation still had a greatly protective effect from being previously infected. So it does not seem to be a doomsday scenario at all. Rather what it seems like is that you might get infected and lightly ill, but you will not have to get to the ICU and will not die.

      There is also the fact that we still don’t have a flurry of documented reinfection cases, as far as we know, it remains anecdotal.

    • Oliver, Thanks for the detailed response. I did see a report the new variant does not account for all current infections.
      But I have to dispute one thing. You are right I think that reinfection reports are anecdotal, technically, because obviously a lot of people did not get PCR tests when sick in June, nor now, but Brazil had testing then, has testing now, and antibody testing in between. It seems extremely unlikely they had big outbreaks of similar diseases coincident with Covod surges.
      I am not someone to carry around a “The End is Near” sign, I am mostly hoping medical profeasionals will spur CDC to implement a true quarantine. Read up on what we are doing, it is totally inadequate, and is apparently being applied only to foreigners, it appears US ciizens can just come right back with no restrictions.
      The chances may not be high but with a plausible doomsday scenario we must do a lot more I think

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