All of the Covid-19 vaccines currently available on the market right now require two doses.
The only one that doesn’t is that of Johnson & Johnson, a single-dose vaccine, but that is still in late-stage clinical testing and will be rolled out soon.
The reason for taking two shots of the available vaccines is because the first time immune cells encounter a potential threat, they need a few weeks to rev up their defensive engines and get their antibodies in gear.
That’s why the first dose of the vaccine is called a priming dose: It’s like an immunological meet-and-greet.
By the time of the second shot, the “boosting dose,” immune cells are already familiar with the general idea of the threat; they just need to fine-tune their antibody response to promote even stronger protection.
Cells that make antibodies, called B-cells, are doing most of their heavy lifting between doses. If B-cells don’t have enough time in between the first dose of a vaccine and the second dose, the antibody protection they generate won’t be as strong.
It’s also possible to be exposed to the actual virus, get the vaccine, and then become sick a few days later, once the virus had time to incubate—which is why it’s crucial to stay vigilant about mask-wearing, hand-washing, and social distancing as prescribed in safety protocols.
It does remain vitally important to get the second dose of the vaccine within six weeks.
Although the first dose generates some protection, the second doses of Pfizer-BioNTech, Moderna, and Sputnik vaccines have been shown to stop more than 9 out of 10 Covid-19 cases. (For now, Sputnik V vaccine is only being used in Russia, Argentina, and Belarus).
After two shots, the AstraZenica and Sinopharm vaccines stop more than 7 out of 10 Covid-19 cases.
To be continued.