Your fear of the prospect of pain. The trip to the clinic is inconvenient and takes time. And the first dose already offers some protection.
Tempted to skip that second dose of your COVID-19 vaccine? Do not do it, experts say. Here’s why.
V: Why do we need two doses?
A: A single dose of Pfizer or Moderna vaccine was 80% effective in preventing infections, according to the CDC’s weekly report on morbidity and mortality on March 29. The effectiveness of the vaccines increased to 90% two weeks after the second dose.
The second dose is an insurance policy.
In the short term, one dose is likely to be good. The reason for a second dose is that you will have a more durable response.
– Peter Chin-Hong, Managing Director, Infectious Diseases Doctor and Co-Dean of Regional Campuses, UCSF
V: What does the second dose do that improves with the first dose?
A: The purpose of the second dose is to train your immune system to respond more quickly to this virus.
I will draw a very simple analogy. If you want to become an expert in whatever field – let’s say, playing the piano – it is not enough to have just one lesson. When you have many lessons, you become much more of an expert.
So if you want your immune system to become an expert to protect you from COVID-19 infection, you want to provide your immune system with several workouts. You can be vaccinated once, but it is not enough.
– Bali Pulendran, Ph.D., Professor of Pathology and Microbiology and Immunology at Stanford
V: If I skip my second dose, how long will I be protected?
A: We know that those who are fully vaccinated are protected for at least six months – and probably at least nine months.
So if you do not get the second dose, your immunity may lapse faster, making you more susceptible to infections. You may not get six to nine months, or even longer, protection. This can be for a shorter period of time, and then it increases the risk of a “breakthrough” infection.
– Dean Blumberg, Managing Director, Professor and Head of Pediatric Infectious Diseases at UC Davis Children’s Hospital
V: What specifically happens to the body after the second dose?
A: There is a huge increase in the amount of neutralizing antibodies.
If you look at the amount of neutralizing antibodies in a drop of blood from someone who has just received a single dose, it could be – I’m just drawing a number – ‘5.’ Once you get the second dose, it can be as much as 500 or 5000.
This is because the immune system is trained and much more is an expert in producing neutralizing antibodies against this virus.
– Bali Pulendran
V: So why is the J&J vaccine only one dose?
A: The J&J vaccine underwent Phase 3 trials as a single-dose vaccine because earlier phase trials showed that it was sufficient to elicit a strong immune response.
After one dose, in all populations, even in older people, the antibody response and T cell response were excellent.
But its effectiveness in preventing 72 to moderate diseases is 72% – lower than the 94-95% reported for the mRNA vaccines. (All vaccines are equally effective in preventing serious illness and death.)
What would happen if we administered the J&J vaccine twice? The company is now conducting a trial to give people two doses to see if it increases its effectiveness.
– Monica Gandhi, Managing Director, Professor of Medicine, UCSF
– Bali Pulendran
V: Why is there a different timing for the second doses for the Pfizer and Moderna vaccines? Pfizer says to wait three weeks; the other is four weeks.
A: The difference in timing is not so much. It’s just a week. This is most likely related to the way the Phase 3 trials were conducted.
– Bali Pulendran
V: Do I have to start over if I cannot get my second dose on time?
A: No. The intervals are based on the clinical trials. They are not absolutely rigid, set in stone.
Of course, one should try to stick to the intervals as much as possible, as recommended by the FDA. But from an immunological perspective, if there is a slight delay of one to two weeks, I would be very surprised if it significantly affects the benefits.
There is still a clear advantage. Better late than never.
– Bali Pulendran
V: I had COVID-19, so why should I bother getting both doses of vaccine?
A: Being infected with the virus stimulates your immune system and provides you with protection.
But it is not clear how long the protection will last. And it is not clear how effective the protection will be. This is not a controlled study. One person may have been infected by only a few viral particles. Another person may have had a much larger dose. We do not yet know what the impact of these differences is on the strength and duration of immunity. This is not the same as injecting someone with a specific dose of the vaccine at a specific time.
Immunity to natural infection is just not that good.
– Bali Pulendran
V: Will both variations of the virus in circulation be enough?
A: Vaccine makers may have a financial incentive for this answer. Pfizer CEO Albert Bourla said in a CNBC interview on Thursday that a likely scenario is that a third dose is needed, between six and twelve months. It is also possible that COVID-19 vaccinations will be annual, just like flu shots.