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The Pfizer-BioNTech Covid-19 vaccine loses some potency against the coronavirus variant that first appeared in South Africa, researchers reported Wednesday, based on lab experiments. 

What the findings mean for how well the vaccine will protect real people from the variant, called B.1.351, is hard to tell. But clinical data from three other vaccines — those from AstraZeneca, Novavax, and Johnson & Johnson — have already shown the shots are not as powerful at blocking symptomatic Covid-19 cases caused by B.1.351 as by other forms of the virus. 


In the new study, which was published Wednesday in the New England Journal of Medicine, researchers from Pfizer, BioNTech, and the University of Texas Medical Branch examined how well blood taken from people who had received the companies’ shot fought off a virus engineered to have the key mutations found in B.1.351. They reported that there was about a two-thirds drop in neutralization power against the variant compared to other forms of the SARS-CoV-2 coronavirus. 

It can be difficult to extrapolate what such lab experiments mean for what happens if someone who received the vaccine is exposed to the variant. For one, these experiments only look at how one arm of the immune system, called neutralizing antibodies, responds to the modified virus. The vaccines generate a range of immune fighters, including other types of antibodies and T cells, so it’s possible that overall people retain more of their defenses in fending off the virus. It’s also possible that even though neutralizing antibodies don’t work as well against the variant, they can still mount enough activity to have an impact. 

Moreover, vaccines that are less effective against B.1.351 or other variants that may emerge may still protect people from getting severe Covid-19; it’s just that they’re not as powerful against milder disease.


But based on the available data, some experts fear that the immunity elicited by vaccines won’t last as long against B.1.351 as against other variants, and that the immunizations won’t be able to drag down transmission of B.1.351 as well as they appear to be limiting the spread of other variants.

Already, vaccine makers are working on booster shots specifically targeting B.1.351 or that could defend against multiple strains of the coronavirus, and regulators are considering how the updated shots could be authorized without needing to go through the full gamut of clinical trials. 

In a statement, Pfizer and BioNTech noted that “there is no clinical evidence to date” that their vaccine doesn’t work as well against B.1.351. “Nevertheless, Pfizer and BioNTech are taking the necessary steps, making the right investments, and engaging in the appropriate conversations with regulators to be in a position to develop and seek authorization for an updated mRNA vaccine or booster once a strain that significantly reduces the protection from the vaccine is identified.”

Moderna, the maker of the other Covid-19 vaccine authorized in the United States, last month reported that its vaccine was also less potent against B.1.351 in lab experiments, but said it believed the levels of antibodies generated should still be protective. 

Both the Moderna and Pfizer-BioNTech vaccines finished clinical trials before the emergence of B.1.351 and other variants of concern, so there are no clinical data for how they defend against the newer iterations of the virus. But in their trials, both were shown to be greater than 90% efficacious at preventing symptomatic Covid-19, so some experts have argued that even if they lose some of their oomph against particular variants, they have enough cushion to remain highly protective. But the drops in efficacy in the Novavax and J&J trials against the variant have led some experts to believe that the Moderna and Pfizer-BioNTech vaccines would show similar declines if they were tested against B.1.351 in clinical settings. 

Earlier this month, South Africa halted the rollout of the AstraZeneca vaccine after an analysis showed it only “provided minimal protection” against mild Covid-19, though the data were based on a small number of patients and researchers are still investigating.

  • Thank you for sharing this article. I was scheduled for a Moderna vaccine and that appt was cancelled. I then scheduled another appt with a provider who only had the Pfizer vaccine and I was in a quandary as to whether I should keep the Pfizer appt or wait for a Moderna one. I think I will go with the Pfizer one as a first dose and see if I can get a Moderna for a second dose (as I understand this was quietly approved and makes perfect sense). I prefer Moderna for its higher dosing (100mcgs vs 30 mags for Pfizer).

  • This is a very interesting to scholars. Note that this is a vaccine not a cure. Vaccines tend to show instability depending on several factors such as species. The underlining factor is all vaccines have a degree of protection to what effect only time can tell. The effect of vaccine is measured over time not in time. In a case where we are looking for an immediate results we risk exciting species that may cause illness in the near future. Selenium boast immune system and other species of selenium are carcinogenic.

  • Lay-people pretending to know-it-all about the brand-new Covid vaccines accomplish nothing other than greater chaos. Viruses always mutate, and only human behaviour will curb the mutating effect. While people still visit, party, indulge in unnecessary travel, and balk at something as easy as wearing masks (or half the wearers seem incapable of wearing them PROPERLY), we lackadazical humans are in for a very rough, long ride – while the virus enjoys its feeding frenzy and vaccines can’t beat its progress.

  • So far only only the COVID vaccines of..

    Johnson & Johnson
    AstraZeneca (UK/Sweden)
    Sinovac (China)

    ..have been tested against SARS-CoV2 variants(that developed resistance to immune antibodies) in trials with people(in South Africa or Brazil). Every other vaccine developer is using “lab tests”, that can be skewed for desirable results.

    All the trial results “not in a lab” suggest one thing – all vaccines(no matter what technology was used) based on the original virus variants will be partially ineffective against the new variants.

    Although many have tried to spin the results in favor of the mRNA vaccines(Pfizer/BioNTech and Moderna), suggesting all results are equal. But this is wrong. The efficacy percentages were from different variants and with different definitions of “symptomatic illness” – the only true indicators that the vaccines work “in the real world” are hospitalizations, serious side effects, and death.
    The vaccines that don’t have these outcomes… accomplish what they were designed to do.

    • The only encouraging news I have seen for a few weeks is that Pfizer is now going to develop a supplementary vaccine to deal with the variants, or all the old types AND the variants, and will begin testing it as soon as regulatory authorities give a go-ahead. Moderna had already said it would do the same – and some smaller companies are supposed to be doing it too.
      What I do not see reported is a rough timeline for development and testing, to know about when they might be able to vaccinate against the variants. Will they add it to the current, vaccine, will it be a separate shot? Perhaps they need testing to detemine these questions, but some rough timeline would be nice.

  • I am grateful to Stat and the author for this article. None of it is a surprise, because, reading between the lines of previous reporting, it was all expected.
    Moderna and Pfizer had put out previous statements, based only on test tube experiments, not necessarily even with actual virus, that admitted a much lower reaction to the South African variant, but then concluded with “we still have something, we think it is good enough”.
    Of course, it is not their fault variants arose, but really, should they have put the reassuring spin on it, or said “We do not know, these variants are a big worry, we are working on it” ? I think the latter.
    Looking at the foreign news reports – the US reports, except for Stat and Nature and such are completely inadequate – it appears the outbreak in the south of England is now in Holland and spreading fast. They told us the “UK variant” would not reinfect those previously sick from Wuhan, or vaccinated, but now there are at least TWO UK variants, and the one they are calling “Bristol” seems to have an immunity-escaping mutation. So far, the US is supposed to have “Kent” which is around 3 times worse than “Wuhan” because it is up to 70% more contagious and 70% more lethal. News reports from England showed a young nurse saying she saw far more young people sick and dying in this outbreak than the previous one. Hard to find stats on that so far. As an aside – IF some of the protection young people have in the US is due to learned immunity to some virus which circulates less in older people – or due to a vaccine such as MMR – then an escape mutation may make them vastly more vulnerable – a true disaster could be looming.

    It looks like the Kent variant is going to cause another severe outbreak, worse than the first one in some ways, here in the US, very soon, and then, for all we really know, the Bristol and/or South African and/or Braizilian (no one seems willing to talk about that one, it appears worse than all the rest based on the 2nd outbreak in Manaus) may each cause their own outbreaks – they share many of the same mutations, so we can hope there will be cross resistance, but we do not know that. Even still, if the vaccines do not stop them, they will cause a combined severe outbreak a few months after the “UK” variants do.

    I do not post this to be the voice of doom, but to point out – we did not do enough to keep these variants out of the country – we had completely inadequate protocols at the borders – an honor system – rather than guarding travelers as Israel, New Zealand, Australia, heck, even HAWAII -have done – and now we have multiple variants set to possibly cause a new major epidemic here, unless we get lucky and our vaccines stop them.

    I blame the previous administration, but at some point, frankly, WHERE IS THE CDC?

  • The UK variant and the US variant have recombined to form a new variant. Probably after years fro now, a new variant that is deadlier and more contagious that the UK variant will emerge from all these mutation an recombination.

    Awhile back some commenters are sprouting the nonsense that the covid19 virus are mutating to become more infectious but less deadly. The UK virus produce higher load which means more damage at the cellular level since each virus can hijack and kill a cell.

    It sad to see that people. just take whatever they read on the news and accept it as facts without thinking and analyzing data, especially contradicting data.

    People tend to accept whatever on the news as fact, making it easier for the media to manipulate and dupe the public.

    Now Biden and Harris are making the same move that you see in most newcomer in a company, blame the previous person/administration they replace as having not done enough. This is so that they can escape blame for if they mess up.

    Biden and Harris, please stop playing the political game. It will tarnish the good think that you are doing in mandating mask and speeding up virus distribution. Stop whining live a child. We are not interested in blame but in action since the more people are vaccinated the less the change of mutations and recombinations. If you focus your energy on actions instead of political maneuvering, you can get more done and be more credible.

    For the Democrats and Pelosi, please stop your obsession about impeachment, it is a waste of time and distraction from the current pandemic. Please let go of your vindictiveness and act for the people and not for the Democratic Party. This is a time of needs. We lose the windows to control the virus at the beginning of the pandemic. Lets not lose the window to control the mutations and recombinations.

    • Tarsi, epidemiological data do not suggest that the UK variant is more deadly. That is still an unknown. It is reasonable to suggest that a variant with greater transmissibility may be associated with less severe symptoms; since transmissibility relies on spreading among hosts, and as people may feel less severely ill, they may be out and about in the world more often with a very infectious but less severe virus.

      All that to say, it’s unfounded to make such blanket statements. The reality is we don’t know what we don’t know. We don’t know if in vitro data on vaccine efficacy against the variants translates into real-world implications, we don’t know if the variants are significantly more deadly or severe than the original Wuhan isolate. We DO know that masks are protective and that mass vaccination efforts are a very real way of ending or containing the pandemic.

    • @Wendy. It seems you don’t have the correct data. The UK produce higher viral load, that means there are more cellular damage. I did not mentioned anything about transmissibility but the higher viral load that it produces on the infected people.

      Please sort out you data. Higher viral load means more cellular damage. Why, because each virus is capable of hijacking all cell in your bodies that contain ACE2. All the cell it hijack will end up undergoing apoptosis.

      Please do not sprout misinformation on things that you seems to know little about.

    • @Wendy. Why does UK variant have high transmissibility? Because it mutations cause it to have more spikes, binds tighter to the cell, and enter the cell more easily. Aside from the facts that infected people ends have having higher viral load.

      All of this points to greater cellular damage to the body.

    • Absolutely right Tarsi. There is something seriously wrong with the Democrats failing to address the Covid situation, by continuing to seek retribution on Trump. Forget Trump and focus on doing the best for the USA.

    • Tarsi,

      If President Trump had done his job, he probably would not be receiving this criticism, because the Biden administration does not appear to be doing what you are doing – using the pandemic to promote a political agenda.

      Nature covered the many problems created by President Trump in the following article from October, so there has been more damage by President Trump since the article was published. Nature is a science journal, not a political one, so it takes someone as dangerous as President Trump to get them to write such a critical article about a politician.

      “How Trump damaged science — and why it could take decades to recover”

      Your attempt to excuse the complete disaster that was President Trump’s handling of the pandemic is the political attack, not President Biden’s accurate explanation of the problems left by the Trump administration. If President Trump had done his job, he would not left such a disorganized mess, but the entire administration was a disorganized mess. They were either afraid of acting independently or lacked the authority to do anything without the dominus vobiscum from President Trump. Why didn’t he do what he promised?

      President Trump closed the pandemic preparedness office; claimed there were only a few cases of COVID and that there would soon be none; promoted dangerous and ineffective treatments, such as hydroxychloroquine, oleandrin, and ingesting disinfectants. These actions did not help, but only distracted people from effective treatments and from prevention, such as wearing a mask.

      President Trump exacerbated the problem when he set the example of refusing to wear a mask, stating that he would not wear one, and only giving in to pressure to behave responsibly much later. President Trump should have worn a mask as soon as they were recommended, in order to set the example for the country, but he refused – until his refusal became politically embarrassing.

      We were supposed to have 20 million doses of vaccines administered in 2020, but we ended up with fewer than 5 million doses administered. This is part of what President Trump was supposed to be doing, but he failed. President Trump appears to have been too busy turning his press conferences into campaign rallies, to do his job.


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