Exit from the race

Merck has stopped testing coronavirus vaccines

Polina Loseva, N+1

Merck has announced the failure of the first phase of testing of its coronavirus vaccines. It was assumed that the drugs would last longer than others, and would require a single injection. However, according to the developers, the vaccines turned out to be safe, but not immunogenic enough.

There are quite a few newcomers among the companies that came first in the coronavirus vaccine race. For example, for Moderna and BioNTech – the developer of the drug for Pfizer – this is the first approved vaccine. It is all the more surprising that they managed to overtake the giants who have been in this market for a long time.

One of these giants, Merck, has recently received approval for the world's first Ebola vaccine. It is already being used in Africa to contain outbreaks of infection, which still occur from time to time. Vaccine against Ebola is based on the vesicular stomatitis virus: it "infects" human cells with the ebolavirus protein and multiplies inside cells for some time, which allows increasing the concentration of foreign protein. The cells themselves do not suffer, and the effect fades over time.

Merck entered into the development of coronavirus vaccines with the same strategy. The company has created two drugs – V590 and V591 – based on the same vesicular stomatitis virus, as well as neutralized measles virus. The use of replicating vectors – that is, viruses that continue to multiply in cells – could give this vaccine a significant head start, since none of the currently approved vaccines works on this principle. The developers believed that only one dose of Merck's drug would be required for vaccination, and immunity could be persistent – because for some time the cells would continue to produce foreign proteins.

However, it did not come to the test of immunity for resistance. According to the results of the first phase of the trials, the researchers said that the concentration of antibodies in the blood of the participants was too low – lower than those who got sick naturally or received another vaccine. And although it is still unknown how many antibodies are needed to get reliable protection against infection, the developers felt that it makes no sense to continue testing – especially given how fast their competitors are moving forward.

Perhaps the failure of the Merck vaccine is due to the fact that it, like other coronavirus vaccines, was designed for intramuscular administration. This hypothesis was expressed by the president of the International Initiative for the Development of an HIV Vaccine, Mark Feinberg. The vesicular stomatitis virus in the vaccine had to selectively penetrate into cells carrying an ACE2 receptor on the surface, which is also used by the coronavirus. However, there are few such cells in muscle tissue. Probably, if the developers had thought about an oral or intranasal delivery method, the effect would have been more noticeable.

Nevertheless, Merck representatives said that they will continue to explore the possibility of using their vaccines – who knows what other pathogens humanity will have to protect against in the near future. In addition, two of the company's drugs intended for the treatment of COVID-19 are currently in the third phase of trials – one antiviral and one immunomodulatory.

Among Merck's other recent successes is the human papillomavirus vaccine, which was approved in 2018 in USA even for adults. At one time, this vaccine was accused of causing brain damage, but then these accusations were refuted – as well as suspicions that the vaccine is associated with autoimmune diseases.

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