As the vaccine rollout continues, experts still have concerns regarding mutated "variants" of SARS-CoV-2 and how they may evade antibodies and therapies.
What parts of the virus do COVID-19 vaccines and therapies target?
There is a spike protein on the surface of SARS-CoV-2 that allows the virus to find and latch on to a human cell. Almost all COVID-19 vaccines use this protein as the means to stimulate an immune response.
In addition to vaccines, companies have manufactured antibodies directed to a specific region of the spike protein called the receptor-binding domain. Authorized for emergency use in patients, these treatments aim to decrease symptoms, decrease the amount of virus in the nasopharynx (the back of the nose where it meets the throat), and prevent patients from being hospitalized.
Virologists are studying whether these antibodies could also serve as surrogates for a vaccine and whether, if administered prophylactically, they could prevent infection.
Why do viruses mutate and create new variants? Are current vaccines and treatments effective against new variants?
Mutations, changes in the genetic sequence of a virus, are a consequence of infection. The longer the virus is able to percolate in the population, the more chances it has to mutate, and the more evolutionary pressure there is for the virus to mutate to survive. Even though the mutation rate of SARS-CoV-2 is about 30 times slower than that of the influenza virus, the high number of global infections has led to mutations. Viruses usually mutate to cause milder illness because it is to the virus's advantage to keep their hosts alive in order to spread the virus and infect more people.
According to the Centers for Disease Control and Prevention (CDC), studies suggest that antibodies generated by vaccines currently authorized in the U.S. recognize the variants of concern identified as of April 2021.
However, laboratory studies from Columbia University, led by virologist David Ho (BS '74), predict that some variants of SARS-CoV-2 could present a challenge for existing antibody therapies and vaccines. The data showed that some of the antibodies that were produced by the human body following the Moderna and Pfizer-BioNTech vaccines were no longer effective against a variant first identified in South Africa. Two of the antibody treatments currently available were found to be ineffective against that variant but still retained effective activity against another.
The lab is conducting additional studies to determine if people who were infected with the original strain of SARS-CoV-2 are prone to reinfection with the variants. More research is necessary to determine whether existing vaccines could still protect against disease even if they do not protect against infection.
What SARS-CoV-2 variants have been identified?
Scientists in the United Kingdom first reported the detection of the B.1.1.7 variant in December 2020. They estimate it emerged in September 2020 and it quickly became the dominant variant of the virus in England. The Centers for Disease Control and Prevention reports B.1.1.7 has spread to at least 120 countries. It was first identified in the U.S. in December 2020 and as of April 2021 represented a growing proportion of cases.
The variant B.1.351 was first identified in South Africa in October 2020 and spread to the U.S. at the end of January 2021. As of April 2021, it was found in at least 64 countries and accounted for the majority of infections in South Africa.
Could companies develop new vaccines against variants?
Use of mRNA platform technology, such as that used in the Pfizer-BioNTech and Moderna vaccines, allows companies to create a new vaccine, or a booster, more quickly than with viral-vector or protein-based methods. Those companies have begun adjusting the vaccines to target the variants and are testing these adjustments in animals. The clinical trial process is shorter for adjusted vaccines, compared to the trial process used to obtain emergency-use authorization.
What is a "pancoronavirus" vaccine, and how might it protect against variants and other types of coronaviruses?
SARS-CoV-2 belongs to a larger family of coronaviruses, which usually cause mild to moderate upper-respiratory tract illnesses such as the common cold. Most coronaviruses have regions of their spike proteins in common. Therefore, a vaccine potentially could be designed to target those common regions and provide protection against many types of coronaviruses.
Research groups, including the Bjorkman Lab at Caltech, are designing such vaccines. The challenge they face: When a vaccine stimulates the immune system, it tends to produce antibodies that target the receptor-binding domain (RBD), the region at the tip of the protein spike where the protein binds to the host cell. But that region is not necessarily the same across different coronaviruses. Nonetheless, it might be possible to create a vaccine against one sub-grouping of coronaviruses—SARS-like betacoronaviruses—by targeting a portion of the RBD that is less variable. It seems likely, though, that a pancoronavirus vaccine would need to trigger immune responses that target non-RBD regions of the spike protein.
Vaccines that can protect against many coronaviruses could prevent another pandemic