The corona crisis poses special challenges for all of us. Last but not least, science: never has a vaccine been searched for so intensively and quickly as now in the case of the SARS-CoV-2 virus. The development times for vaccines including approval are normally several years. A vaccine against SARS-CoV-2 may be available early next year. Several vaccine candidates have now shown promising results.
mRNA vaccines: with new technology against the virus
Several research groups are currently working in parallel on vaccines against the coronavirus. A crucial factor in a vaccination is that the immune system then produces sufficient antibodies against the virus. These can prevent the pathogen from entering the cell and multiplying. The cellular immune response must also be activated.
So-called mRNA vaccines, which contain building instructions for parts of the spike protein of the virus in the form of a so-called messenger RNA (mRNA), have been given particular attention in recent weeks. The mRNA is absorbed by the human cells, which then begin to produce and release the viral protein in the body. The immune system can then specifically form antibodies against the coronavirus protein.
In March 2020, the US company Moderna started a clinical study with an mRNA vaccine, in which 45 participants had different doses of a vaccine called mRNA-1273. After two weeks, all test persons had developed the first antibodies against the virus, reports Moderna now. In eight of the participants, similarly high antibody concentrations were found after about five weeks as in recovered Covid-19 patients.
“ These preliminary data demonstrate that vaccination with mRNA-1273 at the lowest dose of 25 micrograms elicits an immune response that is similar in magnitude to that of a natural infection“, Says Tal Zaks from Moderna. However, it remains to be seen whether this is sufficient to effectively protect against infection. Next, the vaccine will prove itself in a phase II study with more subjects. This study has apparently already been approved and should begin shortly. The efficacy of the vaccine can only be investigated in a phase III study, which is scheduled for July 2020.
DNA vaccine as an alternative
A US Israeli research team, on the other hand, is working with a DNA vaccine in which the DNA of the spike protein is administered by SARS-CoV-2. This is then translated into the viral protein in the body. According to a recent study, the researchers were able to use their vaccine to effectively protect rhesus monkeys against Covid-19. The animals received three doses of vaccine within three weeks. Three weeks later, they were injected with high doses of the virus in their noses and bronchi. In contrast to an unvaccinated control group, the animals did not develop Covid-19 and had a significantly reduced viral load. Antibody levels were also similar to that of recovered Covid 19 patients. However, approval for a study with human subjects is still pending.
Conventional dead vaccines are also in the running
In contrast, two Chinese research teams have decided to use an older method of vaccination against SARS-CoV-2: a classic dead vaccine. The inactivated coronavirus is used to trigger immunization in the body. The results of a successful vaccination trial in rhesus monkeys were published in early May.
The animals received three vaccine doses of killed SARS-CoV-2 viruses and were then confronted with high doses of the virus. The result: the monkeys did not become ill, developed high antibody concentrations and the virus could not multiply in their lungs. A phase I trial with the vaccine called PiCoVacc started in mid-April. A second group has been testing a similar vaccine in Wuhan since the end of April in a phase II study.
Carrier virus brings viral proteins into the cells
A team from the University of Oxford and the U.S. National Institutes of Health (NIH) works with a carrier virus that injects the gene for the spike protein of SARS-CoV-2 into the cells. Existing vaccines against Ebbola and tuberculosis also work according to this pattern.
In a test with rhesus monkeys, the researchers were already able to elicit a cellular and antibody-based immune response with a dose of the vaccine candidate christened ChAdOx1. The monkeys did not get sick either and had solid antibody levels. The Phase I trial started in the UK on April 23.
Vaccine not before 2021
With previous vaccines against other coronaviruses – specifically MERS and SARS – researchers were able to observe the so-called “antibody mediated enhancement”. With this phenomenon, only inaccurately matching antibodies are formed, which could possibly even make an infection worse. So far, there have been no such observations among vaccine candidates against SARS-CoV-2.
However, the results should not be overestimated yet. It remains to be seen whether one of the vaccines will be approved and produced. A cross-population vaccination will probably not be available until early 2021 at the earliest. Phase II and III studies are significantly more complex and longer than the first tests, in which only the tolerability of the vaccines was examined.