In a paper published November 15, 2004, ferrets were vaccinated with an experimental vaccine of recombinant modified vaccinia virus Ankara (rMVA) (a cowpox virus vector) which expressed the SARS-CoV spike (S) protein – the target antigen. Upon challenge, 14 days after booster dose, the vaccinated ferrets “developed a more rapid and vigorous neutralizing antibody response” (in 3 days) compared to the unvaccinated, first time exposed to SARS-CoV virus, control animals who took 7 days to develop neutralizing antibodies.

Vaccine manufactures consider antibody titres, that is the measure of an immune response, to be “an essential feature” for determining an effective prophylactic vaccine or “protection potential” – generating antibodies is a measure of  vaccine “protection” or “efficacy”. However is it really?  When challenged with SARS-CoV virus via intranasal route, the vaccinated ferrets exhibited a “strong inflammatory response” in their liver causing “severe hepatitis”, which was noted as “mild” in the unvaccinated animals.

The paper notes:

  •  “It is known that neutralizing antibodies induced by the S protein of feline infectious peritonitis virus (also a coronavirus) often lead to accelerated infection by the mechanism of antibody-dependent enhancement of virus infectivity”
  • The “neutralizing activity [IgG] was detected in sera collected from all three ferrets 7 days after booster immunization [2nd dose] with rMVA-S virus, while the titre declined to undetectable level 14 days after the booster.”!
  • The “memory immune response, …is difficult to evaluate in mice”, which is why they chose ferrets.
  • Replication of SARS-CoV in ferrets, lasted up to 22 days after challenge infection – thus the vaccine didn’t stop transmission potential!
  • “Coronavirus S is the major antigenic protein responsible for inducing neutralizing antibody response”
  • “Extra caution should be taken in proposed human trials of SARS vaccines“
  • They never re-challenged the control group (now naturally immune ferrets), to investigate whether “severe hepititis” would also occur following infection.