Health In Focus
  • Synthetic horsepox virus has been developed, which has the potential to be used in a smallpox vaccine instead of the vaccinia virus
  • It appears to be a safer alternative to the vaccinia virus
  • It provided mice protection against vaccinia virus infection.

Scientists have synthesized a horsepox virus which could effectively replace the current vaccinia virus in the smallpox vaccine. The study was published in PLOS ONE.

The current smallpox vaccine that contains the vaccinia virus is used only in first responders and military personnel, given the fact that the infection has been eradicated. The side effects of the vaccine include mild reactions like fever, soreness in the arm, enlarged lymph nodes in the armpit, or more serious reactions like allergic reaction, serious rash or even inflammation of the brain (encephalitis) or heart /pericardium (myocarditis/pericarditis or both) in rare cases. Serious adverse effects may be particularly noted in immunocompromised individuals, patients with chronic skin diseases or active skin breaks at the time of the vaccination.
Potential Use of Synthetic Horsepox Virus in Smallpox Vaccines and Cancer Therapy

Scientists felt that another pox virus, the horsepox virus that does not cause infection in humans, could be a safer alternative to the vaccinia virus in the smallpox vaccine. The horsepox virus appears to have a common ancestry with the modern vaccinia virus strains, which are used to develop the smallpox vaccine. However, since the horsepox virus is not easily available, the scientists decided to use large-scale gene synthesis to produce the virus.

Despite several challenges, the scientists were able to synthesize the horsepox virus in cells infected with Shope fibroma virus (SFV). The replicating synthetic-chimeric horsepox virus (scHPXV):
  • Produced smaller plaques and less secondary plaque formation in vitro testing, which indicates the reduced virulence of the virus
  • Was less virulent in mice as compared to a strain of vaccinia virus used in vaccines
  • Provided protection against infection from the vaccinia virus
These findings provide evidence that the synthetic virus can be used instead of the current vaccinia virus in the smallpox vaccine, resulting in a safer yet effective alternative. Further studies on the horsepox vaccine are required before it can be confirmed that it will be useful in humans.

The scientists have also suggested another possible positive implication of their study in a totally unrelated condition, cancer. Ongoing research has used viruses to boost the immune system to fight against cancer cells. Thus, a similar approach as used in the current study could be employed to develop other pox viruses like orthopoxviruses, which could be used in cancer treatment. The synthesis of viral DNA in the laboratory can also help scientists to study some features of the viral genome that have not been completely understood as yet.

About Vaccines

 Vaccines contain live attenuated or killed organisms (or sometimes toxins) that stimulate the immune response and protect the individual against the particular infection. In rare cases, especially in patients with reduced immunity, live attenuated vaccines can cause the infection they were meant to protect against.

Reference :
  1. Noyce RS, Lederman S, Evans DH (2018) Construction of an infectious horsepox virus vaccine from chemically synthesized DNA fragments. PLOS ONE 13(1): e0188453.(

Source: Medindia

Most Popular on Medindia