If a vaccine does its job, it will produce a strong immune response in the patients inoculated with it -- driving the body to make antibodies to the illness in question. But different groups of people may react in different ways to any given vaccine.

In the case of COVID-19, it's particularly important that a vaccine be capable of generating antibodies well in older people, since they tend to suffer worse outcomes more often when infected with the novel coronavirus.

Thursday brought a bit of positive news on that front: Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX) revealed that their leading coronavirus vaccine candidate, BNT162b2, appears to be generating antibodies in its study subjects at higher concentrations than those found in patients who have recovered from COVID-19.

In a phase 1 clinical trial, after receiving two doses of BNT162b2, participants in the 18 to 55 age range had levels of antibodies 3.8 times higher than those found in recovered patients. The 65- to 85-year-olds in the study didn't produce as many antibodies as the younger population, but their antibody levels were still 1.6 times those found in recovered patients.

Gloved hands giving an injection into a shoulder

Image source: Getty Images.

The study also tested a second vaccine candidate called BNT162b1, but Pfizer and BioNTech found that BNT162b2 elicited a more robust immune reaction since it produces a longer viral protein. BNT162b2 also caused side effects less often than BNT162b1, which caused redness and swelling at the injection site in some patients. Subjects given BNT162b1 also had higher levels of fever, fatigue, and chills compared to BNT162b2, and those were more common in older adults.

Pfizer and BioNTech have already enrolled more than 11,000 of the 30,000 subjects it plans to include in the phase 2/3 clinical trial for BNT162b2 that is underway. The drugmakers are hoping they'll have enough data in October to begin seeking a regulatory review.

If regulators determine that BNT162b2 is safe and effective, Pfizer and BioNTech say they are prepared to supply up to 100 million doses -- enough to vaccinate 50 million people -- by the end of this year and approximately 1.3 billion doses by the end of 2021.

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