COVID-19 Vaccine Update: Harvard studies show DNA vaccines provide partial immunity and antibodies prevent reinfection
One thing that the world didn’t know so far was if an infected person who recovers from the infection is safe from reinfection.
The first case of COVID-19 was reported in China in late December. Since then, researchers have been working at breakneck speeds to understand SARS-CoV-2, the COVID-19 causing virus and find a way to neutralise it. However, amidst all the information overload, one thing that the world didn’t know so far was if an infected person who recovers from the infection is safe from reinfection. This is an important aspect as it would determine whether a vaccine would save us from the infection.
Now, two different animal studies conducted at the Center of Virology and Vaccine Research, Beth Israel Deaconess Medical Center, Harvard Medical School, US, indicate that a vaccine may indeed be effective against COVID-19 since antibodies produced in the body once our immune system is exposed to the virus, do protect us against reinfection.
The first study
Since January, the Harvard affiliated Center of Virology and Vaccine Research has reportedly been working with Janssen Pharmaceutica, a pharmaceutical company owned by the multinational company Johnson and Johnson.
For the study, researchers tested at least six prototype DNA vaccine candidates against SARS-CoV-2. All of these candidates express different variants of the spike protein of COVID-19 causing virus. These included: a full-length spike protein (S), one with deletion of the transmembrane domain and cytoplasmic tail (S.dTM), one with deletion of cytoplasmic tail (S.dCT), a receptor-binding domain with a foldon trimerization tag (RBD), one with S1 domain of the spike protein with a foldon trimerization tag (S1), and a prefusion stabilized soluble ectodomain with deletion of the furin cleavage site, two proline mutations, and a foldon trimerization tag (S.dTM.PP)
A total of 35 rhesus macaques were part of the trial, out of which 20 were given an intramuscular injection of one of the vaccine candidates in a 5 mg dose at week 0 and a boost immunisation at week three and the other 10 with sham controls. At week five, all of the vaccinated animals showed the presence of neutralising antibodies in their blood. The neutralising antibody titers (measure of antibodies) in the vaccinated animals were comparable to those developed in convalescent humans and macaques with COVID-19 infection. As per the study, the median titers in all candidates was 74 (in S and S.dCT candidates it was 170) as compared to the median titer of 106 in convalescent (recovering) macaques and 93 in a group of 27 convalescent humans.
In week six, all the animals were challenged with the virus through both intranasal and intratracheal route. All the vaccinated animals (especially the S group) showed a quick and effective immune response with a major reduction in viral loads in the BAL (lower respiratory system) fluids and nasal swabs and only mild clinical symptoms.
The study mentioned that the vaccine did not seem to be providing sterilising immunity but it may help the immune system quickly control the infection on exposure to the virus. Also, the vaccine developed a Th1 immune response, which shows up against intracellular parasites like viruses.
The second study
In the second study done on rhesus macaques, a research team led by Senior Research Associate Abhishek Chandrashekhar found that infection caused by SARS-CoV-2 creates enough antibodies that they can prevent reinfection after recovery.
For this study, the researcher team infected 9 rhesus macaques (6-12 years) with 1ml dose of SARS-CoV-2 virus in various concentrations through the intranasal and intratracheal route. The normal lifespan of these monkeys is about 25 years.
With the first infection, all the monkeys showed symptoms of a mild disease without fever and respiratory difficulty but the virus was found in both the BAL and nasal swabs of the monkeys and signs of pneumonia were seen in their lungs. The viral RNA peaked in the body by day 2 and gradually cleared from the BAL by day 14 and from the nasal swab by day 21 to 28.
All the monkeys showed neutralising antibodies titer of 100 by day 35 regardless of how much the initial dose of the virus was. The antibodies were against various parts of the virus.
After day 35, all the monkeys were again given the same doses of the virus. The study added 3 new animals to keep as positive controls. Very low viral RNA was found in the reinfected groups on day 1 and one animal even showed no viral RNA. On the other hand, all animals in the positive control had a lot of viral RNA.
In the reinfected group, the amount of viral RNA was higher in the nasal swab than the BAL fluid, but even that reduced quite rapidly. Additionally, the reinfected group showed little to no clinical symptoms of the disease. All the reinfected animals showed quick immune response following the rechallenge with the neutralising antibody titters being way higher than after the primary challenge.
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