Australia has been hit by a wave of Covid, following a delta community outbreak. On Sunday, the government announced that an asylum worker had tested positive for COVID-19 despite receiving the first dose of the vaccine on May 12.
Another person also tested positive after taking Pfizer. The fact that both people become infected after taking the first dose means that both doses are needed. Clinical evidence shows that protection against the vaccine is optimal and it takes about two weeks after the second dose for the vaccine to work. This means that vaccines:
-protect against serious cases and death of healthy persons
-dramatically reduce the symptoms of COVID-19
-reduce the possibility of infection with the virus
also reduces the possibility of transmitting the virus to other people
Both doses provide more protection against Covid-19 but there is a risk of becoming infected or transmitting the virus again.
How effective is a single dose of Pfizer?
Clinical trials of the Pfizer vaccine were conducted to test the efficacy of the vaccine more than one week after the second dose. However, these trials revealed that a single dose could provide protection 12 days after vaccination.
Also a single dose is very effective against hospitalization four weeks after vaccination. Meanwhile, previous studies and reports suggest that a first dose of Pfizer may be 50% and 90% effective in preventing infection, reports abcnews.al
Preliminary data also suggest that people who become infected with SARS-CoV-2 after a dose of the Pfizer vaccine are up to 50% less likely to transmit the virus to other members of their family.
How effective is a single dose of AstraZeneca?
The AstraZeneca vaccine was originally developed as a single dose vaccine and has an effectiveness of up to 76% against the virus. Real-world data, although not yet reviewed by colleagues, have shown that one dose is approximately 65% effective in protecting against infection and up to 50% effective in preventing vaccinated people from transmitting the virus if infected.
Also a single dose of AstraZeneca vaccine protects against hospitalization four 4 weeks after vaccination, reports abcnews.al
Which is more effective?
Despite changes in RNA vaccines like Pfizer and vector viral vaccines like AstraZeneca, both vaccines take time to generate antibody responses. After a single dose of AstraZeneca, antibodies can be detected after 14 days and more added over the next two weeks.
But how long does our body need to react? When researchers study the antibody response after receiving the first dose of an anti-Covid vaccine, they find that it takes at least ten days for the immune system to start producing antibodies that can recognize the SARS-CoV-2 spike protein.
It also takes at least a week for T cells, a type of white blood cell important to our immune response, to start responding to the vaccine. Over the coming weeks, these responses become even stronger.
In contrast, the second dose activates the immune system much faster. Within a week after taking the second dose, antibody levels increase by more than tenfold, providing much stronger and more lasting protection against infection. The first dose of an anti-COVID vaccine stimulates our immune system to produce antibodies, but the second dose is essential to ensure that the immunity is strong and stable.
Partial vaccination can be dangerous
While a single dose of each vaccine offers several benefits, partial vaccination for people who are most at risk is problematic. It is also important that health care workers, and people who work and live in asylums, be fully vaccinated as soon as possible.
Another challenge is that all current anti-COVID vaccines are based on the original strain of the virus, but variants now make up the majority of infections in many countries. Some variants do not respond to vaccines, especially after just one dose, reports abcnews.al
Preliminary data suggest that while two doses of the Pfizer vaccine are 88% effective against variant B.1.617.2, a single dose is only 33% effective.
A similar variant called B.1.617.1, is the main factor behind the current outbreak in Victoria and may have the same effect. It is also worth noting that immune responses to a single dose of the Pfizer or AstraZeneca vaccine decrease with age.
In a joint analysis by Pfizer and AstraZeneca, seniors had lower protection rates than young people after a single dose, although seniors were just as protected as young people after two doses.
According to this study, timely administration of the second dose is especially important for the elderly. abcnews.al