It takes time to develop a vaccine

The pandemic of Covid-19 is caused by the infamous virus SARS-CoV-2, better known as novel coronavirus. Scientist from all over the world are doing their best to develop efficient treatments against it, but we will be fully safe only when a vaccine will be available. In this article I update you about the strategy that will be followed to develop it. It won’t help in this first wave of the disease, but it will be essential if the virus will establish in the population (that is highly possible). The take-home message is clear: it takes time to develop a vaccine. Let’s see it with an example from the recent past. In 2009, there was a pandemic of swine flu caused by a variant of H1N1 influenza virus. For vaccine producers it was easy to switch from a trivalent seasonal one against flu to a more efficient strain-specific, because all protocols and release criteria are well established. Anyway, it took 6 months before the vaccine was available. About the novel coronavirus, it is estimated that at least 12-18 months will pass before we see a vaccine released.

Multiple ways to create a vaccine

A vaccine is a biological preparation that provides immunity against a specific disease, without causing the disease itself. This is achieved by exposing the organism to either the full virus, or to parts of it. In the first case, the vaccine is called attenuated if the virus is alive but powerless, inactivated if the virus is killed through exposure to heat or some chemical. In the second case, the organism is exposed to an antigen, which is a specific protein of the virus, or to segments of its genetic material. In all cases, an immune response is generated, with consequent production of specific antibodies against the pathogen. This protects the organism when the real pathogen will try to infect it. Before being approved, a vaccine needs to prove first that is effective with no toxicity or side effects on animals; then successful candidates undergo three phases of clinical trials to prove efficacy and safety on humans as well. 

Vaccine for the novel coronavirus: required features

Let’s see now some important features to consider when developing a vaccine for the novel coronavirus:

  1. We learnt from SARS and MERS epidemics that the Spike protein on the virus surface is the ideal target
  2. Most tested vaccines against SARS-CoV-1 (responsible of SARS epidemic and close relative to SARS-CoV-2) were effective in protecting the animals exposed to the virus, but they didn’t induce sterilizing immunity. This means that the virus was able to begin the infection before being eradicated. Therefore, we need to make sure that the vaccine for SARS-CoV-2 is fully safe before releasing it. It is worth mentioning that information about SARS-CoV-1 candidates ends at phase I of clinical trials, because the extinction of the disease made irrelevant the continuation of the tests. 
  3. Another relevant issue is the waning of the antibody response. Like for other coronaviruses, also SARS-CoV-2 in few cases was able to reinfect the same person. This means that sometimes the immune system cannot maintain the memory against the virus, and the vaccine will need to overcome this issue. 
  4. A fourth point is the most sensitive target. Covid-19 is more lethal for elderly people, who therefore need stronger protection. This might complicate the development: in fact, older individuals are less responsive to vaccines because of immune senescence.

Vaccine for the novel coronavirus: the current status

Because of the dramatic situation, scientists rushed to develop potential vaccines. One week ago Moderna Therapeutics (based in Massachusetts, US) introduced a first candidate in clinical trials. It’s currently being tested on a group of 45 people between 18 and 55 years old. Different doses in two administrations with a gap of 28 days are going to be evaluated. The candidate is called mRNA-1273 and is based on a specific type of genetic material, called “messenger RNA” (mRNA in short), because it delivers information to the cell: mRNA contains specific instructions to build a unique protein. mRNA-1273 forces the cell to produce the Spike protein, which in turn provokes an immune response. How could Moderna Inc. be that fast? On the 10th of January, the genomic sequence of the virus was released, and the company activated right away to exploit the novel information. They designed an mRNA able to encode a safe version of the Spike protein, and it took only 42 days to get one ready. If mRNA-1273 passes efficacy and safety tests in clinical trials, it could be available at some point in 2021, but considering that no mRNA vaccines have ever been approved so far, it might be challenging. Anyway, this candidate already passed efficacy and toxicity tests on animals.

Beyond Moderna efforts, approximately 30 more preclinical tests on animals are ongoing, led by companies or universities.

Hopefully at least one of these candidates will succeed. Fingers crossed!