Results, published in The Lancet, revealed that the vaccine is safe, causes few side effects and induces strong immune responses in both parts of the immune system in the fight against COVID-19, which is caused by SARS-CoV-2.

A T cell response (a cellular immune response) was provoked within 14 days of vaccination and an antibody response within 28 days. Researchers say that an ideal SARS-CoV-2 vaccine should be effective after one or two vaccinations, confer protection for a minimum of 6 months and reduce onward transmission of the virus to contacts.

“The immune system has two ways of finding and attacking pathogens — antibody and T cell responses,” lead author and Oxford professor Andrew Pollard said in a news release. “This vaccine is intended to induce both, so it can attack the virus when it’s circulating in the body, as well as attacking infected cells. We hope this means the immune system will remember the virus, so that our vaccine will protect people for an extended period. However, we need more research before we can confirm the vaccine effectively protects against SARS-CoV-2 infection, and for how long any protection lasts.”

Currently, the results from the trial are too preliminary to confirm whether the new vaccine meets those requirements, but Phase 2 (United Kingdom) and Phase 3 trials (UK, Brazil, South Africa) are taking place to confirm how effective the candidate is in protecting against infection.

Oxford’s new trial included 1,077 healthy adults between 18 and 55 years old with no history of COVID-19 infection across five UK hospitals between April 23 and May 21. The data reported in The Lancet covered the first 56 days of the ongoing trial.

The participants either received the new COVID-19 vaccine candidate (543 total recipients) or the meningococcal conjugate vaccine (534 people). Additionally, 113 participants (among whom 56 received the COVID-19 vaccine and 57 were in the control group) were asked to take paracetamol before and for 24 hours after their vaccination to help reduce vaccine-associated reactions.

Participants were split into four groups, with 88 people in “Group 1” receiving additional safety monitoring with assessment of antibody and T cell responses. Group 2 (412 people) had extra blood taken to assess for antibody and T cell responses, while Group 4 (567 people) had serum taken for antibody response observation only. Among those groups, half the participants received the COVID-19 vaccine and half received the control.

Group 3 (10 people) received only the COVID-19 vaccine and were given an extra dose 28 days after the first dose to determine safety and whether it boosted antibody and T cell responses.

After observing no serious adverse events, the researchers deemed the vaccine to have an acceptable safety profile. The most commonly reported reactions were fatigue and headache, with 70% of all participants given the COVID-19 vaccine only reporting fatigue and 68% reporting headache. Other side effects included pain at the injection site, muscle ache, malaise, chills, feeling feverish and high temperature.

Participants who took paracetamol around their vaccination had reduced pain, chills, feeling feverish, muscle ache, headache and malaise in the 2 days after vaccination, while side effects were less common after the second dose in the 10 people who received the additional one. Taking paracetamol did not affect the immunogenicity of the vaccine candidate.

The researchers found that the vaccine produced strong antibody and T cell responses, with T cell responses targeting the SARS-CoV-2 spike protein markedly increased, although the level slightly declined to the median by day 56. The T cell response did not increase with the second dose in those 10 patients, which researchers say is consistent with other vaccines of this kind.

Antibody responses peaked by day 28 and remained high until day 56 in those given a single vaccine, with a boost in those who received a second dose.

At day 28, in those with a single dose of the vaccine candidate, 32 of 35 participants had neutralizing antibody responses when measured in MNA80 neutralization assay, while 35 out of 35 had those responses when measured in PRNT50 neutralization assay.

The study is being done in collaboration with AstraZeneca (NYSE:AZN), the pharmaceutical company working with Oxford to develop and manufacture the vaccine candidate.

“We are encouraged by the Phase I/II interim data showing AZD1222 was capable of generating a rapid antibody and T-cell response against SARS-CoV-2,” AstraZeneca executive VP of biopharmaceuticals R&D Mene Pangalos said in a release. “While there is more work to be done, today’s data increases our confidence that the vaccine will work and allows us to continue our plans to manufacture the vaccine at scale for broad and equitable access around the world.”

Pfizer (NYSE:PFE) also announced today that the German Phase I/II study for its COVID-19 vaccine candidate, developed in collaboration with BioNTech (NSDQ:BNTX) also suggested safety and T cell responses.

The study of 60 healthy adults between 18 and 55 had 12 subjects per dose level vaccinated with the BNT162b1 vaccine candidate on day 1 and day 22.

According to a news release, the vaccine candidate elicited high, dose level-dependent SARS-CoV-2-neutralizing titers and RBD-binding IgG concentrations after the second dose. Additionally, all subjects in the prime-boost cohorts, except for two at the lowest dose level, had CD4⁺ T cell responses, while 29 of 36 tested subjects mounted an RBD-specific, functional CD8⁺ T cell response.

“It is encouraging that the data on BNT162b1 from the German study cohort are very much in line with what we have seen in the U.S. study cohort,” BioNTech chief medical officer & co-founder Dr. Özlem Türeci said in the release. “The preliminary data indicate that our mRNA-based vaccine was able to stimulate antibody as well as T cell responses at remarkably low dose levels. We believe both may play an important role in achieving effective clearance of a pathogen such as SARS-CoV-2.”