why it’s important you get your second dose ?

- 2021-11-16-

Vaccination is the safest way to gain immunity to the coronavirus, and with most COVID-19 vaccines, you need two doses to get the greatest possible protection. Vaccine refrigerator is the safest way to the vaccine.

Immunologists call this method of giving people multiple doses “prime-boosting”. Essentially, you first teach the immune system what it is looking for – you prime it with the first vaccination. Then, after the immune system has had time to respond to the priming, it is challenged again. The immune response learned the first time is boosted when put into practice on the second exposure.

Most (though not all) vaccines – COVID-19 or otherwise – use prime-boosting to maximise protection. Some even require further doses. This is because immunity can wane over time or, as is the case with the flu vaccine, the virus that causes the disease can change so that the original vaccine no longer provides good protection.

With COVID-19, we have strong evidence that taking a second dose increases your defence against the disease. Despite this, one in 40 people in the UK who have had a first dose don’t seem to be getting their second. In the US, there have been reports of millions of people skipping their second doses. In doing so, these people are endangering their health.


The benefits of prime-boosting with COVID-19 vaccines were initially seen in clinical trials. Early studies of the currently approved COVID-19 vaccines compared the immune responses in people who received one or two vaccine doses. Results showed that after the second dose, people had higher amounts of antibodies to fight the virus, indicating that taking more than one dose would probably increase vaccine effectiveness.

Larger clinical trials then continued with this prime-boosting regimen. With the Pfizer/BioNTech vaccine, protection against symptomatic COVID-19 was found to be 52% from 12 days after the first dose (immunity takes time to build). Protection then rose to 95% after the second dose.

With the rollout of COVID-19 vaccines across many countries worldwide, we’re now getting real-world data that confirms the benefits of prime-boosting that were recorded in trials. A recent British preprint – a piece of research not yet reviewed by other scientists – found that from 21 days after the first vaccine dose, coronavirus infections were reduced by 66% in people receiving the Pfizer/BioNTech vaccine and by 61% in those taking the Oxford/AstraZeneca vaccine. But in people who had also taken second doses, these reductions then fell further to 80% and 79% respectively.

The importance of having two doses is even more evident when looking at hospitalisation rates for COVID-19. Another recent preprint from Public Health England suggests that protection against needing hospital treatment for COVID-19 caused by the delta variant goes up from 94% with one dose to 96% with two doses of the Pfizer/BioNTech vaccine. The difference is even more marked for the Oxford/AstraZeneca vaccine, with protection rising from 71% to 92% with a second dose.

Although these findings are yet to be formally published, the evidence is strong that getting a second vaccine dose raises your protection against getting ill and developing serious illness. Meanwhile, the new dominance of the delta variant has also made the lower protection offered by a single dose even lower than it was before. Making that second trip to the vaccine clinic is therefore critically important.