Loading...
dcyphr | Vaccines for SARS-CoV-2: Lessons from Other Coronavirus Strains

Abstract

It is essential to find a vaccine for COVID-19. COVID-19 is a potentially lethal coronavirus like SARS and MERS. As of April 2020 there is no available vaccine. Knowledge from SARS and MERS can be used for developing COVID-19 vaccines. This study investigates how research from similar coronaviruses can be applied to COVID-19. 

Introduction

Coronaviruses are viruses that belong to the family Coronaviridae. They have a single RNA strand. Their genome size is relatively large. Coronaviruses infect mammals and birds. It can cause symptoms such as lung disease and diarrhoea. In humans, it can be fatal. 

In 2002-2003 SARS emerged in southern China. It had 8096 cases and 774 deaths. The scientific community was unable to develop an accessible vaccine for it. SARS cases stopped being reported from 2004.

In 2012 MERS emerged in Saudi Arabia. It had 2494 cases with 858 deaths. MERS cases are still reported however, there has not been a major outbreak since 2015. There is no accessible vaccine for MERS.

There are varying reasons for the lack of commercial vaccines. MERS likely has no vaccines because of costs for effective animals models. Additionally, MERS is not spread globally. Thus, diseases like HIV and tuberculosis are likelier to be investigated. Similarly, SARS has not been reported since 2004.

COVID-19 was first reported in Wuhan, China in December 2019. According to the World Health Organisation there are 1,669,595 cases worldwide. COVID-19 has also killed 106,138 people. COVID-19 has mild symptoms but may becomes severe in those with other conditions.

Vaccine efforts for SARS and MERS could be useful towards COVID-19. This study focusses on active immunity as it works long-term. This study is based on previous research alone.

Vaccine for SARS Virus

After SARS, several labs started to develop vaccines. Most of these vaccines target a specific protein in the virus. These proteins allow the virus to enter a human cell. Therefore, a vaccine targetting this protein will prevent the virus from entering human cells.

Different types of vaccines were studies. Inactivated vaccines use the entire virus in a weakened state as the vaccine. These viruses are designed to not replicate or be less infectious. 

The researchers believe that only inactivated-virus vaccines reached the clinical stage. To know if a vaccine is effective, vaccinated people and animals are exposed to the disease. Since SARS was dangerous, there were no human studies. Thus, we don't know how effective these vaccines are.

Vaccines for MERS

There are many vaccines under development for MERS. Most target the same protein as in SARS. Various types of vaccines have been tested in animal models. The researchers believe that only DNA-based vaccines reached clinical trials. 

Vaccines for COVID-19

The disease emerged recently. This means that no clinical stage has been completed. The World Health Organization says that 41 vaccines are under development. There is not much information regarding these vaccines. By March 13, 2020, there was only one vaccine in clinical trials.

Toward Protective Vaccines for Clinically Relevant Coronavirus Strains

Vaccine development effort for SARS and MERS should help towards COVID-19. This section describes important information this experiments obtained.

Animal Models

A lack of suitable animal models slowed down, vaccine development for SARS and MERS. This is because the virus could not severely infect animals. This meant that it was not possible to determine the effectiveness of vaccines.

There were 2 main solutions for this. 1. Transgenic animals. These animals have human cells in them which are susceptible to the virus. 2. A mouse-adapted coronavirus modelled the illness similarly to humans. Transgenic mouse models for SARS and MERS are now available.

Non-human primates also did not develop similar symptoms as humans. However, in some species there are limited symptoms. This has allowed analysis of the viability of vaccines.

Correlates of Protection

Few studies have discussed the potential of long-term protection using a vaccination regime.

Natural Infection of Coronavirus Strains

Exposure to SARS and MERS can show possible mechanisms of protection. In humans a fast immune response was related to disease severity and recovery time. This shows that an immune response needs to be triggered to recover from the disease.

It would be ideal for a vaccine to give long term protection. Debates are ongoing whether this can be achieved by vaccination or exposure to the disease. However, certain relevant cells have been detected up to 24 months after infection.

Safety

Studies about the safety of SARS and MERS vaccines are rare. In SARS vaccines, some adverse effects have been seen in animals.

Some SARS vaccinated animals were not protected from MERS and vice-versa.

Areas of Opportunity in Vaccine Development

Experiments comparing different vaccine types are rare. Some studies found equal or varying degree of protection in mice and primates with different vaccine types. It is difficult to determine what vaccine type would be more or less protective.

Some types of coronavirus have never been tested clinically. There are also new technologies for new types of vaccines (mRNA-based). The emergence of new vaccine types means that their effectiveness against coronavirus is unknown.

Conclusions

Vaccine development efforts for SARS and MERS can help COVID-19. An effective vaccine should consider possible adverse effects. Vaccine development efforts should consider the possibility of short term ability to generate an immune response seen in SARS and MERS after an infection. 

Evidence that short term ability to generate and immune response in COVID-19 patients does not mean that an effective vaccine is impossible. This is seen in vaccines for viruses that don't have naturally acquired immunity (eg.smallpox).