An international cohort of researchers is following up on hypothesis already backed by some evidence—early childhood vaccinations, especially for measles, may be protecting children from COVID-19.
While young children and the elderly are almost always at an elevated risk of infectious disease, COVID-19 has turned that idea on its head with all nations reporting much lower incidences of the disease in children compared with adults and the elderly.
The researchers’ hypothesis is backed by the sequence similarity of amino acid residues between glycoproteins of SARS-CoV-2, measles and rubella viruses. Specifically, researchers found striking homology sequence similarity of 30 amino acid residues between the Spike (S) glycoprotein of the SARS-CoV-2 virus with the Fusion glycoprotein of Measles virus, and the envelope glycoprotein of the Rubella virus. SARS-CoV-2 is a single- strand, positive-sense RNA virus. S protein is a key immunogenic protein of SARS-CoV-2 that induces the host immune system; the latter fights off the foreign particles that enter the human body by producing antibodies.
Generally, children are immunized against live-attenuated vaccines of measles and rubella where the entire viral particle is introduced to the child’s immune system to thwart future attacks. This makes the likelihood of shared immunity between vaccine-preventable childhood diseases and COVID-19 even higher as children may be developing a broad enough immunity in response to the vaccines to cover novel diseases.
“The antibodies produced in children due to the MMR vaccine could recognize some epitopes on the SARS-CoV-2 spike proteins. These antibodies, particularly in the epithelial layer of respiratory airways, block binding and entering of the virus into the cells,” said Rimantas Kodzius, a professor at Kaunas University of Technology (Lithuania) and co-author of the recent study published in Frontiers in Molecular Biosciences.
Like COVID-19, measles causes respiratory complications and is transmitted through sneezing and coughing droplets. While the chance of locating epitopes in the 30 amino acid residues that are shared between the COVID-19, measles and rubella viruses is unknown, previous studies on humoral immunity support the researchers’ findings. A 2019 study, for example, illustrated immunity sharing between the Zika and Dengue fever viruses. Additionally, other studies have shown that the levels of antibodies against measles and rubella may persist in the system of an immunized person for 15 to 20 years.
Kodzius said experimental research is the necessary next step to support the hypothesis. He and his team intend to test purified spike protein of SARS-CoV-2 against the polyclonal and monoclonal antibodies of measles and rubella viruses both in vivo and in vitro.
“Understanding the immunological base of children's protection against COVID-19 can prevent and control further spreading the disease,” Kodzius and his co-authors concluded in their paper.