Merck/MSD withdraws two vaccine candidates from further research but continues focus on treatment

Simon Collins, HIV i-Base

On 25 January 2021, the US pharmaceutical company Merck announced that it was withdrawing two vaccine candidates against COVID-19 from further research.

This was due to the candidates – V590 and V591 – generating weaker responses in phase 1 studies compared to those seen after natural infection or to with other (unspecified) vaccines.

V590 was previously being developed in association with IAVI and results from both studies will be reported in peer-reviews journals.

The press release also reported that Merck is continuing to research potential treatments.

These include an antiviral drug called molnupiravir (MK-4482) that is currently in four phase 2/3 studies as treatment and prevention, with results expected by May 2021.

A second compound, MK-7110 (formerly CD24Fc), is being studied to modulate inflammatory response to SARS-CoV-2. Interim phase 3 results reported 50% reduced respiratory failure or mortality in people hospitalised with moderate to severe infection, although these are not yet published.

Further details on both treatment and vaccine candidates are included in the press release.

Outside the US, Merck is known as MSD.


Although the vaccine news is disappointing, this shows the high barrier set by the first vaccines. Even major companies with expertise in vaccine development are challenged with such high thresholds for efficacy and safety.

This doesn’t diminish the need for new candidates that can meet the current global demand. There is also the potential for single-shot coverage, for formulations with easier delivery models than injections. that are easier to transport and that are less expensive.

It highlights that participants in vaccine research should still receive optimal standard of care. This should include the option to be unblinded from a research study if offered the chance of vaccination in the general NHS programme.


Merck press release. Merck discontinues development of SARS-CoV-2/COVID-19 vaccine candidates; continues development of two investigational therapeutic candidates. (25 January 2021).

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