SARS-CoV-2 Californian and English Strains, the Worst Hybridization Scenario

Hybridization between the British and California strains of the SARS-CoV-2 coronavirus appears to have occurred at least once reported by medical sources in the state of California, and it appears that the resulting virus is more powerful than its two predecessors. The COVID-19 pandemic is being a race in the style of the Queen of Hearts from "Alice in Wonderland." This theory is frequently used in biology to make the student understand that species are in a constant evolutionary race to maintain their position in relation to their competitors. Pathogens evolve, primarily through mutations, to gain an advantage over their hosts, while their hosts in turn try to improve evolutionarily to prevent the pathogen from affecting them.

The Queen of Hearts from "Alice in Wonderland"

In this respect, viruses are perhaps the most implacable. Their rapid biological cycle and the ease with which they accumulate mutations mean that a virus in a year has significantly altered its genome to more efficiently evade the defenses of its host. In the slightly more than a year that we have been with the pandemic, we have talked about several strains that had different mutations, the strain that affected minks was one of them and precisely the British one was another that we have discussed. In addition, viruses and other simple organisms can carry out horizontal transmission of genetic material. It is these exchanges between unrelated species that have given some bacteria resistance to antibiotics.

In the case of the crossing of the Californian strain, called B.1.429, and the English strain, B.1.1.7, it seems that they have simply recombined their genetic material at some point where both variants of the virus coincided within the same patient. This cross had been specifically searched since December 2020, but was not observed until early February by P.h. D. Bette Korber -well known computational biologist specializing in the AIDS virus. The sample with the evidence of the mutation comes from California and it is speculated that it could be responsible for a new wave of infections in the golden state. Although it appears that the hybrid virus has not yet spread and has only been found in a sample. In this regard, the discoverers announce that more tests have to be carried out to corroborate the finding and see its possible repercussions.

An illustration showing the hybridization of two coronavirus

The British strain is especially contagious. One of the mutations that characterizes it produces that there is a 70% more load of the virus in blood with respect to other previous variants, increasing its transmission capacity. This is due to a single deletion at position 69/70 (Δ69 / 70). For its part, the California strain is especially difficult to treat since it presents the L452R mutation, a change from a Leucine to an Arginine in position 452. This tiny change produced by the change of a uracil in a guanine in the second position of the triplet entails that the virus has an altered protein on its surface and therefore the antibodies recognize it worse. One of the problems associated with this type of recombination events is that they give one strain several characteristics of another, instead of adding mutations little by little and in such a way that scientific teams can predict the advance of the virus and act accordingly by designing variants of their medications.

The fusion of both strains is not strange, since this process has already been observed in other coronaviruses. This is due to the replication mechanism used by coronaviruses. The host cell RNA polymerase is the machinery that the virus uses to multiply. However, this enzyme complex is known to allow certain alterations. In fact, it is possible for the RNA polymerase to disassemble from the RNA strand that it is copying and then reattach to it to continue. It would be in this situation that an RNA of the British strain would begin to read and, it would disassemble and then bind to an RNA of the Californian strain or vice versa. In principle, this situation is very unlikely since a person would have to be infected independently with the two different strains, which would mean that they would have been exposed to both in a relatively short period of time so that both had the possibility of entering the same cell. If this hybridization has occurred, it would be the first detected for SARS-CoV-2, although specialists already anticipate that this type of event is only a matter of time before it occurs.

In the same way that this hybridization has been detected, the evolution of each strain around the world is being followed with great effort to detect early the accumulating mutations and also the possible recombinations that may occur. Right now there are about 10 important strains or variations of SARS-CoV-2 and if they are not extinguished by vaccines it is a matter of time before some of them hybridize.


Ji, W., Wang, W., Zhao, X., Zai, J., & Li, X. (2020). Homologous recombination within the spike glycoprotein of the newly identified coronavirus may boost cross-species transmission from snake to human. Journal of medical virology.

Ji, W., Wang, W., Zhao, X., Zai, J., & Li, X. (2020). Cross‐species transmission of the newly identified coronavirus 2019‐nCoV. Journal of medical virology, 92(4), 433-440.

Graham, R. L., & Baric, R. S. (2010). Recombination, reservoirs, and the modular spike: mechanisms of coronavirus cross-species transmission. Journal of virology, 84(7), 3134-3146.

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