Currently there are several competing companies that are trying to develop a vaccine for SAR-Cov-2. As each company has said that they are going to engage in at-risk-production if they think that they have a "winner" (begin mass production before clinical trials are completed and before FDA approval), what happens if the (completed) clinical trials show only slight differences in safety and efficacy. Would the FDA approve both vaccines? Has anything like this happened before?

My attempts to research this only seem to lead to the FDA approval process, not whether the FDA has or would approve different vaccines for the same patient group.

(I'm predicating FDA approval for general population use - not an approval for specific individuals or groups).

  • When talking about "winners", restricting your research to the FDA may not help find what you are looking for. There are other parts of the government that may have more to do with picking winners, for example the Biomedical Advanced Research and Development Authority (BARDA)), which was funded to the tune of $3.5 billion to work with private companies on the construction, manufacturing and purchase of vaccines and therapeutics under the in the latest (phase III) round of COVID-19 stimulus. May 21, 2020 at 21:56
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    Why reason do you think they would have to not approve more than one? May 22, 2020 at 3:14
  • @curiousdannii - I'm just curious. I'm hopeful that the FDA is immune to political pressure. Obviously FDA would not approve vaccines that did not work, or vaccines that were unsafe. But for those that are safe, some may be more effective than others. . With so many companies in the (Warp Speed) race and the risks so high (beginning mass production before FDA approval), an environment of fierce competition may ensue. Hopefully prescribers will know which vaccine are more effective than others (after approval).
    – BobE
    May 22, 2020 at 4:34
  • FDA can and have approved multiple similar products form multiple manufacturers: just look at the food industry: multiple companies see FDA approved pasteurized orange juice. But the FDA is not immune to political pressure. Consider the case of the miracle fruit extract - a natural sugarless sweetner that actually grows on plants instead of being manufactured and widely used in East Asia, especially Japan but banned by the FDA partly due to complaints from both the artificial sweetner industry and the sugar industry
    – slebetman
    May 22, 2020 at 5:05
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    Even the regular seasonal flu has multiple distinct vaccines (live, inactivated, injected, nasal spray, etc). It's always good to have options since patient needs differ.
    – bta
    May 22, 2020 at 23:27

3 Answers 3


Definitely. The CDC's website has a list of vaccines used in the USA sorted by disease; you'll notice that many diseases have more than one vaccine.

Note that some vaccines are variations of each-other, but some are clearly distinct vaccines with different active ingredients, for example those approved for Typhoid; Vivotif, taken orally, and TYPHIM Vi, which is injected. Both are FDA approved.

In this case it seems likely that both potential COVID-19 vaccines would be approved if they met the FDA's criteria for approval.

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    FDA approval is not a blessing as THE preferred treatment, so as long as the different vaccines meet the minimum safety and efficacy thresholds, they can all be approved. +1 for the links. May 21, 2020 at 20:01
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    And given the huge numbers of vaccines which will be required, it’s helpful if multiple vaccines with different active ingredients are found, to aid parallel manufacture in existing facilities.
    – Tim
    May 22, 2020 at 9:43

Certainly. Notable examples include the Salk & Sabin vaccines for polio, and Shingrix & Zostavax vaccines for shingles. This is just off the top of my head, so a little research might turn up other examples.

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    From the CDC website (emphasis added) "Shingrix (recombinant zoster vaccine) is the preferred vaccine, over Zostavax® (zoster vaccine live), a shingles vaccine in use since 2006." Moreover Zostavax reduces shingles risk by 51%, while Shingrex reduces the risk by 91%. So while both are approved and provide protection, Shingrex is the decidedly best first choice. (Zostavax was licenced in 2006, Shingrex eleven years later (something better came along??)) BTW, thanks.
    – BobE
    May 22, 2020 at 4:52

There are several lines of vaccines for flu. Two were developed simultaneously for Shingles. On flu it depends on the year which ones are available and approved. On shingles, one made it to market first, but the second one proved more effective and became the preferred vaccine.

As of the candidate process, often many vaccine lines are developed in progress, because usually only a few of them are found to be both safe and effective. Testing for safety is quite easy and quick, but testing for effectiveness can take months. They can't risk putting all their eggs in one basket.

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    Focusing on the shingles vaccine, are you referring to Zostavax and Shingrex? Zostavax was licensed in 2006, Shingrex was licensed in 2017. Shingrex proved to be the more effective, but I suspect that the Shingrex approach wasn't even a contender in 2006. The compressed and urgent time frame for a Coronavirus vaccine will surely pit the pharma manufacturers against one another.
    – BobE
    May 22, 2020 at 18:05
  • Yes, the companies will be actively put against each other, in sort of a bidding war. Early stage development works better with coordination, but making a finished product works better through competition. This is one place the world's pharmaceutical system works well, as early stage development is done by Universities. May 23, 2020 at 1:14

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